The Standard Electrical Dictionary A Popular Dictionary of Words and Terms Used in the Practice of Electrical Engineering (part 3 of 4)

The Standard Electrical Dictionary A Popular Dictionary of Words and Terms Used in the Practice of Electrical Engineering (part 3 of 4)

Fulgurite. An irregular and tubular mass of vitrified quartz, believed to be formed by melting under the lightning stroke.

Fig. 175. CRUCIBLE, ELECTRIC.

Furnace, Electric. A furnace in which the heat is produced by the electric current. It has hitherto been practically used only in the extraction of aluminum and silicium from their ores. The general principle involves the formation of an arc between carbon electrodes. The substances to be treated are exposed to the heat thus produced. Sometimes the substances in the arc form imperfect conductors, and incandescence takes a part in the action. Sometimes the substances are merely dropped through the arc.

[Transcriber's note: Silicium is silicon.]

Fuse Board. A tablet on which a number of safety fuses are mounted. Slate is excellent material for the tablet, as it is incombustible, and is easily drilled and worked.

Fuse Box. A box containing a safety fuse. Porcelain is an excellent material for its base. No combustible material should enter into its composition.

Fuse, Cockburn. A safety fuse or cut off which consists of a wire of pure tin running from terminal to terminal, to whose centre a leaden ball is secured by being cast into position. The connection with the terminals is made by rings at the ends of the wire through which the terminal screws are passed and screwed home. When the tin softens under too heavy a current the weight of the shot pulls it apart.

Fig. 176 COCKBURN SAFETY FUSE.

264 STANDARD ELECTRICAL DICTIONARY.

Fig. 177. ELECTRIC FUSE.

Fuse, Electric. A fuse for igniting an explosive by electricity. There are two kinds. In one a thin wire unites the ends of the two conducting wires as they enter the case of the fuse. The larger wires are secured to the case, so that no strain comes on the fine wire. On passing a current of sufficient strength the small wire is heated. In use the fuse is bedded in powder, which again may be surrounded by fulminating powder, all contained in a copper or other metallic case. Such a detonator is used for exploding guncotton and other high explosives.

The other kind of fuse is similar, but has no thin connecting wire. The ends of the conductors are brought nearer together without touching. In use a static discharge is produced across from end to end of the conductors, igniting a proper explosive placed there as in the other case.

The first kind of fuse is generally operated by a battery or small mechanical generator--the latter by a spark coil, frictional or influence machine or by a Leyden jar.

Galvanic. adj. Voltaic; relating to current electricity or the electrolytic and electro-chemical relations of metals. (For titles in general under this head see Voltaic--or the main title.)

Galvanic Element. A galvanic couple with exciting fluid and adjuncts; a galvanic cell. The word element is sometimes applied to the electrodes of a cell, as the carbon element or zinc element.

265 STANDARD ELECTRICAL DICTIONARY.

Galvanic Polarization. The polarization of a voltaic couple. (See Polarization.)

Galvanism. The science of voltaic or current electricity.

Galvanization. (a) Electroplating or depositing a metal over the surface of another by electrolysis.

(b) In medical electricity the effects produced on any part of the system by the current of voltaic battery. Various descriptive qualifications are prefixed, such as "general" galvanization, indicating its application as applied to the whole body, "local" for the reverse case, and so on.

Galvanization, Labile. Application of the galvanic current in electro-therapeutics where one sponge electrode is employed which is rubbed or moved over the body, the other being in constant contact with the body.

Galvanized Iron. Iron coated with zinc by cleaning and immersion in melted zinc. The iron is prevented from rusting by galvanic action. It forms the negative element in a couple of which the zinc is the positive element. From this electric protective action the name is derived.

Galvano-cautery, Chemical. Electro-therapeutic treatment with sharp electrodes, one of which is inserted in the tissue and a current passed by completing the circuit through the tissue so as to electrolyze or decompose the fluids of the tissue. It is applied in the removal of hair or extirpation of the follicle. The process is not one of heating, and is improperly named cautery.

Galvano-faradization. In medical electricity the application of the voltaic and induced or secondary current simultaneously to any part of the system.

Galvanometer. An instrument for measuring current strength and sometimes for measuring inferentially potential difference, depending on the action of a magnetic field established by the current, such action being exerted on a magnetic needle or its equivalent.

A current passing through a conductor establishes circular lines of force. A magnetic needle placed in their field is acted on and tends to place itself parallel with the lines, in accordance with the principles of current induction. (See Induction, Electro-magnetic.) A common compass held near a conductor through which a current is passing tends to place itself at right angles to such conductor. For a maximum effect the conductor or the part nearest the needle should lie in the magnetic meridian. If at right angles thereto its action will only strengthen the directive force of the earth's induction or magnetic field, as the needle naturally points north and south. Such combination is virtually a galvanometer.

266 STANDARD ELECTRICAL DICTIONARY.

A typical galvanometer comprises a flat coil of wire placed horizontally within which a magnetic needle is delicately poised, so as to be free to rotate with the least possible friction. The needle may be supported on a sharp point like a compass needle, or may be suspended by a long fine filament. It should be covered by a glass plate and box, or by a glass shade. Finally a graduated disc may be arranged to show the amount of deflection of the needle.

In use the apparatus is turned about until the needle, as acted on by the earth's magnetic field, lies parallel to the direction of the coils of wire. On passing a current through the coil the needle is deflected, more or less, according to its strength.

By using exceedingly fine wire, long enough to give high resistance, the instrument can be used for very high potentials, or is in condition for use in determining voltage. By using a coil of large wire and low resistance it can be employed in determining amperage. In either case the deflection is produced by the current.

The needle is often placed above or below the coil so as only to receive a portion of its effect, enough for all practical purposes in the commoner class of instruments.

The galvanometer was invented by Schweigger a short time after Oersted's discovery, q. v.

Galvanometer, Absolute. A galvanometer giving absolute readings; properly one whose law of calibration can be deduced from its construction. Thus the diameter of the coil, and the constants and position of a magnetic needle suspended in its field being known, the current intensity required to deflect the needle a given number of degrees could be calculated.

Galvanometer, Aperiodic. A galvanometer whose needle is damped (see Damping) as, for instance, by the proximity of a plate of metal, by an air vane or otherwise, so that it reaches its reading with hardly any oscillation. A very light needle and a strong magnetic field also conduce to vibrations of short period dying out very quickly. Such galvanometers are termed "dead-beat." No instrument is absolutely dead-beat, only relatively so.

267 STANDARD ELECTRICAL DICTIONARY.

Fig. 178. ASTATIC GALVANOMETER.

Galvanometer, Astatic. A galvanometer with a pair of magnetic needles connected astatically, or parallel with their poles in opposition. (See Astatic Needle.) Each needle has its own coil, the coils being wound in opposite directions so as to unite in producing deflections in the same sense. As there should be some directive tendency this is obtained by one of the magnets being slightly stronger than the other or by the proximity of a fixed and adjustable controlling magnet, placed nearer one needle than the other.

For small deflections the currents producing them are proportional to their extent.

Galvanometer, Ballistic. A galvanometer whose deflected element has considerable moment of inertia; the exact opposite of an aperiodic or dead beat galvanometer. (See Galvanometer, Aperiodic.) All damping by air vanes or otherwise must be carefully done away with.

Fig. 179. SIEMENS & HALSKE'S GALVANOMETER.

Siemens & Halske's galvanometer is of the reflecting or mirror type (see Galvanometer, Reflecting) with suspended, bell-shaped magnet, in place of the ordinary magnetic needle, or astatic combination of the lightest possible weight in the regular instrument. A copper ball drilled out to admit the magnet is used as damper in the ordinary use of the instrument. To convert it into a ballistic galvanometer the copper ball is removed. The heavy suspended magnet then by its inertia introduces the desired element into the instrument.

268 STANDARD ELECTRICAL DICTIONARY.

Referring to the cut, Fig. 179, M is the suspended magnet, with north and south poles n and s; S is the reflecting mirror; r is the tube containing the suspending thread; R is the damper removed for ballistic work.

The ballistic galvanometer is used to measure quantities of electricity in an instantaneous discharge, which discharge should be completed before the heavy needle begins to move. The extreme elongation or throw of the needle is observed, and depends (1) on the number of coulombs (K) that pass during the discharge; (2) on the moment of inertia of the needle and attached parts; (3) on the moment of the controlling forces, i. e., the forces tending to pull the needle back to zero; (4) on the moment of the damping forces; (5) on the moment of the deflecting forces due to a given constant current. The formula is thus expressed:

K = (P / PI ) * A * sin( kº / 2 ) / tan( aº )

in which K = coulombs discharged; P = periodic time of vibration of needle; A = amperes producing a steady deflection equal to aº ; kº = first angular deflection of needle. For accuracy kº and aº should both be small and the damping so slight as to be negligible. Otherwise a correction for the latter must be applied. For approximate work for kº and aº the deflections read on the scale may be used with the following formula:

K = (P / PI ) * ( A / 2 ) * ( kº / aº )

Galvanometer Constant. Assume a galvanometer with a very short needle and so placed with respect to its coils that the magnetic field produced by a current circulating in them is sensibly uniform in the neighborhood of the needle, with its lines of force at right angles thereto. The field is proportional to the current i, so that it may be denoted by G i. Then G is the galvanometer constant. If now the angle of deflection of the needle is ? against the earth's field H, M being the magnetic moment of the needle we have G i M cos ? = H M sin ? or i = (H/G)* tan ?. H/G is the reduction factor; variable as H varies for different places.

For a tangent galvanometer the constant G is equal to 2*PI*(n/a), in which n denotes the number of turns of wire, and a denotes the radius of the circle.

Galvanometer, Differential. A galvanometer in which the needle is acted on by two coils wound in opposition, each of equal deflecting action and of equal resistance. If a current is divided between two branches or parallel conductors, each including one of the coils, when the needle points to zero the resistances of the two branches will bc equal. In the cut, C C' represent the coils, and A and B the two leads into which the circuit, P Q, is divided.

269 STANDARD ELECTRICAL DICTIONARY.

Fig. 180. THEORY OF DIFFERENTIAL GALVANOMETER.

Fig. 181. DIFFERENTIAL GALVANOMETER.

Galvanometer, Direct Reading. A calibrated galvanometer, whose scale is graduated by volts or amperes, instead of degrees.

Galvanometer, Marine. (Sir William Thomson's.) A galvanometer of the reflecting type, for use on shipboard. A fibre suspension is adopted for the needle. The fibre is attached to a fixed support at one end and to a spring at the other, and the needle is suspended by its centre of gravity. This secures it to a considerable extent from disturbance due to the rolling of the ship. A thick iron box encloses the needle, etc., to cut off any magnetic action from the ship. (See Galvanometer, Reflecting.)

Galvanometer, Potential. A galvanometer wound with fine German silver wire to secure high resistance used for determination of potential difference.

Galvanometer, Proportional. A galvanometer so constructed that the deflections of its index are proportional to the current passing. It is made by causing the deflecting force to increase as the needle is deflected, more and more, or by causing the restitutive force to diminish under like conditions, or by both. The condition is obtained in some cases by the shape and position of the deflecting coils.

Galvanometer, Quantity. A galvanometer for determining quantities of electricity, by the deflections produced by discharging the quantities through their coils. It is a ballistic galvanometer with very little or no damping.

270 STANDARD ELECTRICAL DICTIONARY.

Fig. 182. PRINCIPLE OF REFLECTING GALVANOMETER.

Fig. 183. REFLECTING GALVANOMETER.

Galvanometer, Reflecting. A galvanometer the deflections of whose needle are read by an image projected by light reflected from a mirror attached to the needle or to a vertical wire carrying the needle. A lamp is placed in front of the instrument facing the mirror. The light of the lamp is reflected by the mirror upon a horizontal scale above the lamp. An image of a slit or of a wire may be caused thus to fall upon the scale, the mirror being slightly convex, or a lens being used to produce the projection.

271 STANDARD ELECTRICAL DICTIONARY.

If the mirror swings through a horizontal arc, the reflected image will move, in virtue of a simple geometrical principle, through an arc of twice as many degrees. The scale can be placed far from the mirror, so that the ray of light will represent a weightless index of very great length, and minute deflections of the needle will be shown distinctly upon the scale.

In the cut, Fig. 182, the ray of light from the lamp passes through the aperture, m m, and is made parallel by the lens, L. At s is the mirror attached to the needle and moving with it. A scale placed at t receives the reflection from the mirror. The cut, Fig. 183, shows one form of the instrument set up for use.

Synonym--Mirror Galvanometer.

Galvanometer Shunt. To prevent too much current passing through a galvanometer (for fear of injury to its insulation) a shunt is sometimes placed in parallel with it. The total current will be distributed between galvanometer and shunt in the inverse ratio of their respective resistances. (See Multiplying Power of a Shunt.)

272 STANDARD ELECTRICAL DICTIONARY.

Fig. 184. SINE GALVANOMETER.

Galvanometer, Sine. A galvanometer whose measurements depend upon the sine of the angle of deflection produced when the coil and needle lie in the same vertical plane.

The needle, which may be a long one, is surrounded by a coil, which can be rotated about a vertical axis passing through the point of suspension of the needle. Starting with the needle at rest in the plane of the coil, a current is passed through the coil deflecting the needle, the coil is swung around deflecting the needle still more, until the needle lies in the plane of the coil; the intensity of the current will then be in proportion to the sine of the angle through which the coil and needle move.

In the galvanometer M is a circle carrying the coil, N is a scale over which the needles, m and n, move, the former being a magnetic needle, the latter an index at right angles and attached thereto; a and b are wires carrying the current to be measured. The circles, M and N, are carried by a base, O, around which they rotate. H is a fixed horizontal graduated circle. In use the circle, M, is placed in the magnetic meridian, the current is passed through the coil, M; the needle is deflected; M is turned until its plane coincides with the direction of the needle, m. The current strength is proportional to the sine of the angle of deflection. This angle is measured by the vernier, C, on the circle, H. The knob, A, is used to turn the circle, M.

273 STANDARD ELECTRICAL DICTIONARY.

Fig. 185. TANGENT GALVANOMETER.

Galvanometer, Tangent. A galvanometer in which the tangents of the angles of deflection are proportional to the currents producing such deflections.

For this law to apply the instrument in general must fulfill the following conditions:

(1) The needle must be controlled by a uniform magnetic field such as that of the earth;

(2) the diameter of the coil must be large compared to the length of the needle;

(3) the centre of suspension of the needle must be at the centre of the coil;

(4) the magnetic axis of the needle must lie in the plane of the coil when no current is passing.

If a single current strength is to be measured the best results will be attained when the deflection is 45°; in comparing two currents the best results will be attained when the deflections as nearly as possible are at equal distances on both sides of 45°.

The needle should not exceed in length one-tenth the diameter of the coil.

For very small deflections any galvanometer follows the law of tangential deflection.

As for very small deflections the tangents are practically equal to the arcs subtended, for such deflections the currents are proportional to the deflections they produce.

The sensibility is directly proportional to the number of convolutions of wire and inversely proportional to their diameter.

The tangent law is most accurately fulfilled when the depth of the coil in the radial direction is to the breadth in the axial direction as squareRoot(3):squareRoot(2), or about as 11:9.

Galvanometer, Torsion. A galvanometer whose needle is suspended by a long filament or by a thread and spiral spring against whose force of torsion the movements of the needle are produced. The current strength is determined by bringing the needle back to its position of rest by turning a hand-button or other arrangement. The angle through which this is turned gives the angle of torsion. From this the current strength is calculated on the general basis that it is proportional to the angle of torsion.

Fig. 186. TORSION GALVANOMETER.

274 STANDARD ELECTRICAL DICTIONARY.

Galvanometer, Vertical. A galvanometer whose needle is mounted on a horizontal axis and is deflected in a vertical plane. One of the poles is weighted to keep it normally vertical, representing the control. It is not used for accurate work.

Synonym--Upright Galvanometer.

Fig. 187. VERTICAL GALVANOMETER.

Galvanometer, Volt- and Ampere-meter. A galvanometer of Sir William Thomson's invention embodying the tangent principle, and having its sensibility adjustable by moving the magnetic needle horizontally along a scale (the "meter") towards or away from the coil. A curved magnet is used to adjust the control. The leads are twisted to prevent induction.

The instrument is made with a high resistance coil for voltage determinations, and with a low resistance coil for amperage determinations.

At one end of a long base board a vertical coil with its plane at right angles to the axis of the board is mounted. A scale (the "meter" of the name) runs down the centre of the board. A groove also runs down the centre. The magnetic needle is contained in a quadrant-shaped glass-covered box which slides up and down the groove. A number of short parallel needles mounted together, with an aluminum pointer are used.

Fig. 188. SIR WILLIAM THOMSON'S AMPERE-METER GALVANOMETER.

275 STANDARD ELECTRICAL DICTIONARY.

In the cut P is the base board, M is a glass covered case containing the magnetic needle, and sliding along the base board, being guided by the central groove, C, is the coil. Between the coil and the needle is the arched or bent controlling magnet. The long twisted connecting wires are seen on the right hand.

Galvano-plastics. The deposition of metals by electrolysis, a disused term replaced by electro-deposition, electroplating, and electro-metallurgy.

Galvano-puncture. An operation in medical electricity. (See Electro-puncture.)

Galvanoscope. An instrument, generally of the galvanometer type, used for ascertaining whether a current is flowing or not. Any galvanoscope, when calibrated, if susceptible thereof, becomes a galvanometer.

Gas, Electrolytic. Gas produced by the decomposition, generally of water, by electrolysis. It may be hydrogen or oxygen, or a mixture of the two, according to how it is collected. (See Gases, Mixed.)

Gases, Mixed. The mixture of approximately one volume of oxygen and two volumes of hydrogen collected in the eudiometer of a gas voltameter or other electrolytic apparatus.

Gassing. The evolution of gas from the plates of a storage battery in the charging process, due to too high voltage in the circuit of the charging dynamo.

Gastroscope. An apparatus for illuminating by an incandescent lamp the interior of the stomach, and with prisms to refract the rays of light so that the part can be seen. The stomach is inflated with air, if desirable, to give a better view. An incandescent platinum spiral in a water jacket has been employed for the illumination.

Gassiot's Cascade. A goblet lined for half its interior surface with tinfoil. It is placed in the receiver of an air pump from the top of whose bell a conductor descends into it, not touching the foil. On producing a good rarefaction, and discharging high tension electricity from between the conductor just mentioned and the metal of the machine, a luminous effect is produced, as if the electricity, pale blue in color, was overflowing the goblet.

Gauss. A name suggested for unit intensity of magnetic field. Sylvanus P. Thomson proposed for its value the intensity of a field of 1E8 C. G. S. electro-magnetic units. J. A. Fleming proposed the strength of field which would develop one volt potential difference in a wire 1E6 centimeters long, moving through such field with a velocity of one centimeter per second. This is one hundred times greater than Thomson's standard. Sir William Thomson suggested the intensity of field produced by a current of one ampere at a distance of one centimeter

The gauss is not used to any extent; practical calculations are based on electro-magnetic lines of force.

276 STANDARD ELECTRICAL DICTIONARY.

Gauss' Principle. An electric circuit acts upon a magnetic pole in such a way as to make the number of lines of force that pass through the circuit a maximum.

Fig. 189. GAUSS' TANGENT POSITION.

Gauss, Tangent Positions of. The "end on" and "broadside" methods of determining magnetization involve positions which have been thus termed. (See Broadside Method and End on Method.)

Gear, Magnetic Friction. Friction gear in which the component wheels are pressed against each other by electromagnetic action. In the cut, repeated from Adherence, Electro-magnetic, the magnetizing coil makes the wheels, which are of iron, press strongly together.

Fig. 190. MAGNETIC FRICTION GEAR.

277 STANDARD ELECTRICAL DICTIONARY.

Geissler Tubes. Sealed tubes of glass containing highly rarefied gases, and provided with platinum electrodes extending through the glass tightly sealed as they pass through it, and often extending a short distance beyond its interior surface.

On passing through them the static discharge luminous effects are produced varying with the degree of exhaustion, the contents (gas), the glass itself, or solutions surrounding it. The two latter conditions involve fluorescence phenomena often of a very beautiful description.

The pressure of the gas is less than one-half of a millimeter of mercury. If a complete vacuum is produced the discharge will not pass. If too high rarefaction is produced radiant matter phenomena (see Radiant State) occur.

Geissler tubes have been used for lighting purposes as in mines, or for illuminating the interior cavities of the body in surgical or medical operations.

Generating Plate. The positive plate in a voltaic couple, or the plate which is dissolved; generally a plate of zinc.

Synonyms--Positive Plate--Positive Element.

Generator, Current. Any apparatus for maintaining an electric current. It may be as regards the form of energy it converts into electrical energy, mechanical, as a magneto or dynamo electric machine or generator; thermal, as a thermo-electric battery; or chemical, as a voltaic battery; all of which may be consulted.

Generator, Secondary. A secondary or storage battery. (See Battery, Secondary.)

German Silver. An alloy of copper, 2 parts, nickel, 1 part, and zinc, 1 part. Owing to its high resistance and moderate cost and small variation in resistance with change of temperature, it is much used for resistances. From Dr. Mathiessen's experiment the following constants are deduced in legal ohms: Relative Resistance (Silver = 1), 13.92 Specific Resistance at 0° C. (32F.), 20.93 microhms. Resistance of a wire, (a) 1 foot long, weighing 1 grain, 2.622 ohms. 1 foot long, 1/1000 inch thick, 125.91 " 1 meter long, weighing 1 gram, 1.830 " 1 meter long, 1 millimeter thick, 0.2666 " Resistance of a 1 inch cube at 0°C. (32° F.), 8.240 microhms.

Approximate percentage increase of resistance per 1° C. (1.8° F.) at about 20° C. (68° F.), 0.044 per cent.

Gilding, Electro-. The deposition of gold by an electric current, or electrolytically in the electroplating bath.

Gilding Metal. A special kind of brass, with a high percentage of copper, used to make objects which are to be gilded by electrolysis.

278 STANDARD ELECTRICAL DICTIONARY.

Gimbals. A suspension used for ships' compasses and sometimes for other apparatus. It consists of a ring held by two journals, so as to bc free to swing in one plane. The compass is swung upon this ring, being placed concentrically therewith. Its journals are at right angles to those of the ring. This gives a universal joint by which the compass, weighted below its line of support, is always kept horizontal.

Fig. 191. COMPASS SUSPENDED IN GIMBALS.

Glass. A fused mixture of silicates of various oxides. It is of extremely varied composition and its electric constants vary greatly. Many determinations of its specific resistance have been made. For flint glass at 100° C. (212° F.) about (2.06E14) ohms --at 60° C (140° F.) (1.020E15) (Thomas Gray) is given, while another observer (Beetz) gives for glass at ordinary temperatures an immeasurably high resistance. It is therefore a non-conductor of very high order if dry. As a dielectric the specific inductive capacity of different samples of flint glass is given as 6.57--6.85--7.4--10.1 (Hopkinson), thus exceeding all other ordinary dielectrics. The densest glass, other things being equal, has the highest specific inductive capacity.

Gold. A metal, one of the elements; symbol Au. c .; atomic weight, 196.8; equivalent, 65.6; valency, 3; specific gravity 19.5. It is a conductor of electricity.

Annealed. Hard drawn. Relative Resistance (Annealed Silver = 1), 1.369 1.393 Specific Resistance, 2.058 2.094 Resistance of a wire at 0° C. (32°F.) (a) 1 foot long, weighing 1 grain, 57.85 58.84 ohms (b) 1 foot long, 1/1000 inch thick, 12.38 12.60 " (c) 1 meter long, weighing 1 gram, .4035 .4104 " (d) 1 meter long, 1 millimeter thick, .02620 .02668 " Resistance of a 1 inch cube at 0° C.(32° F.) .8102 .8247

Approximate increase in resistance per 0° C., (1.8° F) at about 20° C. (68° F.), 0.365 per cent.

Electro-chemical equivalent (Hydrogen = .0105), .6888

279 STANDARD ELECTRICAL DICTIONARY.

Gold Bath. A solution of gold used for depositing the metal in the electroplating process.

A great number of formulae have been devised, of which a few representative ones are given here. COLD BATHS. HOT BATHS. Water, 10,000 10,000 10,000 10,000 5,000 3,000 Potassium Cyanide, 200 -- 200 10 -- 50 Gold, 100 15 100 10 10 10 Potassium Ferrocyanide, -- 200 -- -- 150 -- Potassium Carbonate, -- 150 -- -- 50 -- Ammonium Chloride, -- 30 -- -- 20 -- Aqua Ammoniae, -- -- 500 -- -- -- Sodium Phosphate, -- -- -- 600 -- -- Sodium Bisulphite, -- -- -- 100 -- --

(Roseleur.)

In the baths the gold is added in the form of neutral chloride, Auric chloride (Au Cl6).

Gold Stripping Bath. A bath for removing gold from plated articles without dissolving the base in order to save the precious metal. A bath of 10 parts of potassium cyanide and 100 parts of water may be used, the articles to be stripped being immersed therein as the anode of an active circuit. If the gilding is on a silver or copper basis, or on an alloy of these metals the same solution attacks the base and dissolves it, which is objectionable. For silver articles it is enough to heat to cherry red and throw into dilute sulphuric acid. The gold scales off in metallic spangles. For copper articles, a mixture of 10 volumes concentrated sulphuric acid, 1 volume nitric acid, and 2 volumes hydrochloric acid may be used by immersion only, or with a battery. The sulphuric acid in such large excess is supposed to protect the copper. For copper articles concentrated sulphuric acid alone with the battery may be used. This does not sensibly attack the copper if it is not allowed to become diluted. Even the dampness of the air may act to dilute it.

Graduator. Apparatus for enabling the same line to be used for telegraph signals and telephoning.

One type consists in coils with iron cores or simply electromagnets. These act to retard the current in reaching its full power and also prolong it. This gives a graduated effect to the signals, so that the telephone diaphragm is not audibly affected by the impulses.

The telephoning current is so slight and so rapid in its characteristic changes that it is without effect upon the ordinary telegraph.

280 STANDARD ELECTRICAL DICTIONARY.

Gram. The unit of weight in the metric system; accepted as the unit of mass in the absolute of C. G. S. system of units. It is the one-thousandth part of mass of a standard weight preserved under proper conditions in Paris, and supposed to be the mass of a cubic decimeter of distilled water at the temperature of the maximum density of water. The standard is the kilogram; the temperature is 3.9º C. (39º F.). The standard kilogram is found to be not exactly the weight of a cubic decimeter of water, the latter weighing 1.000013 kilogram.

If therefore the defined gram on the water basis is taken as the unit it varies very slightly from the accepted gram.

1 gram is equal to 15.43234874 grains. (Prof. W. H. Miller.)

Gram-atom. The number of grams of an element equal numerically to the atomic weight, as 16 grams of oxygen, 1 gram of hydrogen, 35.5 grams of chlorine; all which might be expressed as gram-atoms of oxygen, hydrogen and chlorine respectively.

The gram-atom approximately expresses the number of gram-calories required to heat one gram of the substance 1º C. (1.8º F.). This is in virtue of Dulong and Petit's discovery that the atomic weight of an element multiplied by its specific heat gives approximately a constant for all elements.

[Transcriber's note: A gram-atom is the mass, in grams, of one mole of atoms in a monatomic element. A mole consists of Avogadro's number of atoms, approximately 6.02214E23.]

Gram-molecule. The number of grams of a substance equal numerically to its molecular weight.

Graphite. Carbon; one of three allotropic modifications of this element. It occurs in nature as a mineral.

It is used as a lubricant for machinery; for commutator brushes; for making surfaces to be plated conductive, and for mixing with manganese binoxide in Leclanché cells.

Gravitation. A natural force which causes all masses of matter to attract each other. Its cause is unknown; it is often supposed to be due to the luminiferous ether.

[Transcriber's note: Einstein's explanation of gravity, General Relativity and the curvature of space-time, came 23 years later, 1915.]

281 STANDARD ELECTRICAL DICTIONARY.

Gravity, Acceleration of. The velocity imparted to a body in one second by the action of gravitation at any standard point upon the earth's surface in a vacuum. This will vary at different places, owing principally to the variation in centrifugal force due to the earth's rotation. For standard valuation it must be reduced to sea level. The following are examples of its variation:

Equator, 978.1028 centimeters per second Paris, 980.94 " Greenwich 981.I7 " Edinburgh, 981.54 " Pole (N. or S.), 983.1084 (theoretical) "

As round numbers for approximate calculations 981 centimeters or 32.2 feet may be employed.

[Transcriber's note: The acceleration of gravity at the equator is also reduced by the increased distance from the center of the earth (equatorial bulge). Increased altitude reduces gravity. Reduced air density at altitude reduces buoyancy and increases apparent weight. Local variations of rock density affects gravity.]

Gravity, Control. Control by weight. In some ammeters and voltmeters gravity is the controlling force.

Grid. A lead plate perforated or ridged for use in a storage battery as the supporter of the active materials and in part as contributing thereto from its own substance.

Ground. The contact of a conductor of an electric circuit with the earth, permitting the escape of current if another ground exists.

Ground-wire. A metaphorical term applied to the earth when used as a return circuit.

Fig. 192. GROVE'S GAS BATTERY.

Grove's Gas Battery. A voltaic battery depending for its action on the oxidation of hydrogen instead of the oxidation of zinc. Its action is more particularly described under Battery, Gas. In the cut B, B1 * * * are the terminals of the positive or hydrogen electrodes, marked H, and A, Al * * * are the terminals of the negative or oxygen electrodes marked O, while M, M1 * * * is dilute sulphuric acid.

282 STANDARD ELECTRICAL DICTIONARY.

Guard Ring. An annular horizontal surface surrounding the balanced disc in the absolute electrometer. (See Electrometer, Absolute.)

Guard Tube. A metal tube surrounding a dry pile used with a quadrant electrometer, or other electrometers of that type. It prevents the capacity of the lower brass end of the pile (which brass end closes the glass tube containing the discs) from momentary change by approach of some conductor connected to the earth. There are other guard tubes also.

Gun, Electro-magnetic. An electro-magnet with tubular core. If, when it is excited a piece of an iron rod is pushed into the central aperture of the core and is released, the magnetic circle will try to complete itself by pushing the rod out so that it can thus be discharged, as if from a popgun.

Synonym--Electric Popgun.

Fig. 193. "ELECTRIC POPGUN."

Gutta Percha. The hardened milky juice of a tree, the Isonandra gutta, growing in Malacca and other parts of the Eastern Archipelago. It is much used as an insulator or constituent of insulators.

Resistance after several minutes electrification per 1 centimeter cube at 54º C. (75º F.), 4.50E14 ohms.

The specific resistance varies--from 2.5E13 to 5.0E14 ohms. A usual specification is 2.0E14 ohms. The influence of temperature on its resistance is given in Clark & Bright's empirical formula, R = R0 at, in which R is the resistance at temperature tº C--Ro the resistance at 0º C (32º F), a is the coefficient .8944.

The resistance increases with the time of passage of the current, the variation being less the higher the temperature.

283 STANDARD ELECTRICAL DICTIONARY.

Time of Relative Resistance Relative Resistance Electrification. at 0º C (32º F.) at 24º C (75º F.) 1 minute 100 5.51 2 " 127.9 6. 5 " 163.1 6.66 10 " 190.9 6.94 20 " 230.8 7.38 30 " 250.6 7.44 60 " 290.4 7.6 90 " 318.3 7.66

In cable testing one minute is generally taken as the time of electrification.

Pressure increases the resistance by the formula Rp=R (1+ .00327 P) in which Rp is the resistance at pressure p--R resistance at atmospheric pressure--p pressure in atmospheres. Thus in the ocean at a depth of 4,000 meters (2.4855 miles), the resistance is more than doubled. The longer the pressure is applied, the greater is the resistance.

The specific inductive capacity of gutta percha is 4.2.

Good gutta percha should not break when struck with a hammer, should recover its shape slowly, and it should support much more than 300 times its own weight.

Gyrostatic Action of Armatures. Owing to gyrostatic action a rotating armature resists any change of direction of its axis. On ships and in railway motors which have to turn curves this action occurs. A 148 lb. armature running at 1,300 revolutions per minute may press with 30 lbs. on each journal as the ship rolls through an angle of 20° in 16 seconds.

H. (a) The symbol for the horizontal component of the earth's magnetization.

(b) The symbol for the intensity of a magnetizing force or field. The symbol H, as it is generally used, may mean either the number of dynes which act upon a unit pole, or the number of lines of force per centimeter.

(c) The symbol for the unit of self-induction.

Hair, Removal of, by Electrolysis. A method of depilation by destruction of individual hair follicles by electrolysis.

A fine platinum electrode is thrust into a hair follicle. It is the negative electrode. The positive electrode is in contact with the body of the person under treatment; it is often a sponge electrode simply held in his hand. A current of two to four milliamperes from an E. M. F. of 15 to 20 volts, is passed. This destroys the follicle, the hair is removed and never grows again. A gradual increase of current is advised for the face. As only one hair is removed at once, but a small number are taken out at a sitting.

284 STANDARD ELECTRICAL DICTIONARY.

Haldat's Figures. With a pole of a strong bar magnet, used like a pencil, imaginary figures are drawn upon a hard steel plate, such as a saw-blade. The pattern is gone over several times. By dusting iron filings on a sheet of paper laid over the steel plate, while horizontal, very complicated magnetic figures are produced.

Hall's Experiment. A cross of thin metal, such as gold leaf, is secured upon a pane of glass. To two opposite arms a battery is connected in circuit with them. To the other two arms a galvanometer is connected in circuit. If the cross is put into a field of force whose lines are perpendicular thereto, the galvanometer will disclose a constant current. The current is pushed, as it were, into the galvanometer circuit. Other metals have been used with similar results. They must be thin or the experiment fails. If the arm receiving the battery current is horizontal, and if it flows from left to right, and if the lines of force go from downward through the cross, the current in the galvanometer circuit will flow from the observer through the other arms of the cross, if the cross is of gold, silver, platinum or tin, and the reverse if of iron. The experiment has indicated a possible way of reaching the velocity of electricity in absolute measure.

Hall Effect. The effect observed in Hall's experiment, q. v.

Hall Effect, Real. A transverse electro-motive force in a conductor through which a current is passing produced by a magnetic field.

Hall Effect, Spurious. A spurious electro-motive force produced in a conductor, through which a current is passing by changes in conductivity of the conductor brought about by a magnetic field.

Hanger Board. A board containing two terminals, a suspending hook, and a switch, so that an arc lamp can be introduced into a circuit thereby, or can be removed as desired.

Harmonic Receiver. A receiver containing a vibrating reed, acted on by an electro-magnet. Such a reed answers only to impulses tuned to its own pitch. If such are received from the magnet it will vibrate. Impulses not in tune with it will not affect it. (See Telegraph, Harmonic.)

Head Bath, Electric. A fanciful name for an electro-medical treatment of the head. The patient is insulated by an insulating stool or otherwise. His person is connected with one terminal of an influence machine. An insulated metallic circle, with points of metal projecting inward or downward, is placed about the head. The circle is connected with the other pole of the machine. On working it a silent or brush discharge with air convection streams occurs between the patient's head and the circle of points.

285 STANDARD ELECTRICAL DICTIONARY.

Head-light, Electric. An electric head-light for locomotives has been experimented with. It includes the parabolic reflection of the regular light with an arc-lamp in place of the oil lamp. An incandescent lamp may be used in the same place, but has no great advantage over oil as regards illuminating power.

Heat. A form of kinetic energy, due to a confused oscillatory movement of the molecules of a body. Heat is not motion, as a heated body does not change its place; it is not momentum, but it is the energy of motion. If the quantity of molecular motion is doubled the momentum of the molecules is also doubled, but the molecular mechanical energy or heat is quadrupled.

As a form of energy it is measured by thermal units. The calorie is the most important, and unfortunately the same term applies to two units, the gram-degree C. and the kilogram-degree C. (See Calorie.) Calories are determined by a calorimeter, q. v.

Independent of quantity of heat a body may be hotter or colder. Thermometers are used to determine its temperature.

Heat is transmitted by conduction, a body conducting it slowly for some distance through its own substance. Bodies vary greatly in their conductivity for heat. It is also transmitted by convection of gases or liquids, when the heated molecules traveling through the mass impart their heat to other parts. Finally it is transmitted by ether waves with probably the speed of light. This mode of transmission and the phenomena of it were attributed to radiant heat. As a scientific term this is now dropped by many scientists. This practice very properly restricts the term "heat" to kinetic molecular motion.

The mechanical equivalent of heat is the number of units of work which the energy of one unit quantity of heat represents. (See Equivalents, Mechanical and Physical.)

Heat, Atomic. The product of the specific heat of an element by its atomic weight. The product is approximately the same for all the elements, and varies as determined between 5.39 and 6.87. The variations are by some attributed principally to imperfection of the work in determining them. The atomic heat represents the number of gram calories required to raise the temperature of a gram atom (a number of grams equal numerically to the atomic weight) one degree centigrade.

286 STANDARD ELECTRICAL DICTIONARY.

Heat, Electric. This term has been given to the heat produced by the passage of a current of electricity through a conductor. It is really electrically produced heat, the above term being a misnomer.

The rise of temperature produced in a cylindrical conductor by a current depends upon the diameter of the conductor and on the current. The length of the wire has only the indirect connection that the current will depend upon the resistance and consequently upon its length.

The quantity of heat produced in a conductor by a current is in gram-degree C. units equal to the product of the current, by the electro-motive force or potential difference maintained between the ends of the wire, by .24.

The cube of the diameter of a wire for a given rise of temperature produced in such conductor by a current is equal approximately to the product of the square of the current, by the specific resistance (q. v.) of the material of the conductor, by .000391, the whole divided by the desired temperature in centigrade units.

Heat, Electrical Convection of. A term applied to the phenomena included under the Thomson effect, q. v., the unequal or differential heating effect produced by a current of electricity in conductors whose different parts are maintained at different temperatures.

Heater, Electric. An apparatus for converting electrical energy into thermal energy.

An incandescent lamp represents the principle, and in the Edison meter has been used as such to maintain the temperature of the solutions. Heaters for warming water and other purposes have been constructed, utilizing conductors heated by the passage of the current as a source of heat. (See also Heating Magnet.)

Heating Error. In voltmeters the error due to alteration of resistance of the coil by heating. If too strong a current is sent through the instrument, the coils become heated and their resistance increased. They then do not pass as much current as they should for the potential difference to which they may be exposed. Their readings then will be too low. One way of avoiding the trouble is to have a key in circuit, and to pass only an instantaneous or very brief current through the instrument and thus get the reading before the coils have time to heat.

The heating error does not exist for ammeters, as they are constructed to receive the entire current, and any heating "error" within their range is allowed for in the dividing of the scale.

Heating Magnet. An electro-magnet designed to be heated by Foucault currents induced in its core by varying currents in the windings. It has been proposed as a source of artificial heat, a species of electric heating apparatus for warming water, or other purposes.

287 STANDARD ELECTRICAL DICTIONARY.

Heat, Irreversible. The heat produced by an electric current in a conductor of identical qualities and temperature throughout. Such heat is the same whatever the direction of the current. The heating effect is irreversible because of the absence of the Thomson effect, q. v.) or Peltier effect, q. v.

Heat, Mechanical Equivalent of. The mechanical energy corresponding to a given quantity of heat energy. Mechanical energy is generally represented by some unit of weight and height, such as the foot-pound; and heat energy is represented by a given weight of water heated a given amount, such as a pound-degree centigrade. Joule's equivalent is usually accepted; it states that 772.55 foot pounds of mechanical energy are equivalent to 1 pound-degree F. (one pound avds. of water raised in temperature one degree Fahrenheit). Other equivalencies have also been deduced.

Heat, Molecular. The product of a specific heat of the compound by its molecular weight. It is approximately equal to the sum of the atomic heats of its constituent elements.

The molecular heat represents the number of gram calories required to raise the temperature of a gram-molecule (a number of grams equal numerically to the molecular weight) one degree centigrade.

The molecular heat is approximately equal for all substances.

Heat, Specific. The capacity of a body for heat; a coefficient representing the relative quantity of heat required to raise the temperature of an identical weight of a given body a defined and identical amount.

The standard of comparison is water; its specific heat is taken as unity. The specific heats by weight of other substances are less than unity. The specific heat varies with the temperature. Thus the specific heat of water is more strictly 1+.00015 tº C.

Specific heat is greater when a substance is in the liquid than when it is in the solid state. Thus the specific heat of ice is 0.489; less than half that of water. It differs with the allotropic modifications of bodies; the specific heat of graphite is .202; of diamond, .147.

The product of the specific heat by the atomic weight of elements gives a figure approximately the same. A similar law applies in the case of molecules. (See Heat, Atomic-Heat, Molecular.)

The true specific heat of a substance should be separated from the heat expended in expanding a body against molecular and atomic forces, and against the atmospheric pressure. So far this separation has not been possible to introduce in any calculations.

288 STANDARD ELECTRICAL DICTIONARY.

Heat, Specific, of Electricity. A proposed term to account for the heat absorbed or given out in unhomogeneous conductors, by the Thomson effect, or Peltier effect (see Effect, Thomson--Effect, Peltier.) If a current of electricity be assumed to exist, then under the action of these effects it may be regarded as absorbing or giving out so many coulombs of heat, and thus establishing a basis for specific heat.

Heat Units. The British unit of heat is the pound degree F--the quantity of heat required to raise the temperature of a pound of water from 32° to 33° F.

The C. G. S. unit is the gram-degree C.; another metric unit is the kilogram-degree C. The latter is the calorie; the former is sometimes called the small calorie or the joule; the latter is sometimes called the large calorie. The term joule is also applied to a quantity of heat equivalent to the energy of a watt-second or volt-coulomb. This is equal to .24l gram degree calorie.

Hecto. A prefix to terms of measurement--meaning one hundred times, as hectometer, one hundred meters.

Heliograph. An apparatus for reflecting flashes of light to a distant observer. By using the Morse telegraph code messages may thus be transmitted long distances. When possible the sun's light is used.

Helix. A coil of wire; properly a coil wound so as to follow the outlines of a screw without overlaying itself.

Fig. 194. LEFT-HANDED HELIX.

Fig. 195. RIGHT-HANDED HELIX.

Henry. The practical unit of electro-magnetic or magnetic inductance. It is equal to 1E9 C. G. S., or absolute units of inductance. As the dimensions of inductance are a length the henry is equal to 1E9 centimeters, or approximately to one quadrant of the earth measured on the meridian.

Synonyms--Secohm--Quadrant--Quad.

289 STANDARD ELECTRICAL DICTIONARY.

Hermetically Sealed. Closed absolutely tight. Glass vessels, such as the bulbs of incandescent lamps, are hermetically sealed often by melting the glass together over any opening into their interior.

Heterostatic Method. A method of using the absolute or attracted disc electrometer. (See Electrometer Absolute.) The formula for its idiostatic use, q. v., involves the determination of d, the distance between the suspended and fixed discs. As this is difficult to determine the suspended disc and guard ring may be kept at one potential and the lower fixed disc is then connected successively with the two points whose potential difference is to be determined. Their difference is determined by the difference between d and d', the two distances between the discs. This difference is the distance through which the micrometer screw is moved. The heterostatic formula is:

V' - V = (d' - d)* squareRoot( 8*PI*F / S )

in which V and V' are potentials of the two points; d' and d the two distances between the discs necessary for equilibrium; S the area of the disc and F the force of attraction in dynes. (See Idiostatic Method.)

High Bars of Commutator. Commutator bars, which in the natural wear of the commutator, project beyond the others. The surface then requires turning down, as it should be quite cylindrical.

High Frequency. A term used as a noun or as an adjective to indicate in an alternating current, the production of a very great number of alternations per unit of time--usually expressed as alternations per second.

Hissing. A term applied to a noise sometimes produced by a voltaic arc; probably due to the same cause as frying, q. v.

Hittorf's Solution. A solution used as a resistance. It is a solution of cadmium iodide in amylic alcohol. Ten per cent. of the salt is used. It is contained in a tube with metallic cadmium electrodes. (See Resistance, Hittorf' s.)

Fig. 196. HITTORF'S RESISTANCE TUBE.

290 STANDARD ELECTRICAL DICTIONARY.

Holders. (a) The adjustable clamps for holding the armature brushes of dynamos and motors.

(b) The clamps for holding the carbons of arc lamps.

(c) The clamps for holding safety fuses, q. v.

(d) Holders for Jablochkoff candles and other electric candles. (See Candle Holders.)

(e) A box or block of porcelain for holding safety fuses.

Hood. A tin hood placed over an arc-lamp. Such hoods are often truncated cones in shape, with the small end upwards. They reflect a certain amount of light besides protecting the lamp to some extent from rain.

Horns. The extensions of the pole pieces of a dynamo or motor. (See Following Horns-Leading Horns.)

Synonym--Pole Tips.

Horse Power. A unit of rate of work or activity. There are two horse powers.

The British horse power is equal to 33,000 pounds raised one foot per minute, or 550 foot pounds per second, or 1.0138 metric horse power.

The metric horse power (French) is equal to 75 kilogram-meters, or 542 foot pounds per second, or .986356 British horse power.

H. P. is the abbreviation for horse power. (See Horse Power, Electric.)

Horse Power, Actual. The rate of activity of a machine, as actually developed in condition for use. It is less than the indicated or total horse power, because diminished by the hurtful resistances of friction, and other sources of waste. It is the horse power that can be used in practise, and which in the case of a motor can be taken from the fly-wheel.

Horse Power, Electric. The equivalent of a mechanical horse power in electric units, generally in volt-amperes or watts; 745.943 watts are equivalent to the activity of one British horse power; 735.75 are equivalent to one metric horse power. The number 746 is usually taken in practical calculations to give the equivalency.

[Transcriber's note: Contemporary values are: Mechanical (British) horsepower = 745.6999 Watts; Metric horsepower = 735.49875 Watts]

Horse Power, Indicated. The horse power of an engine as indicated by its steam pressure, length of stroke, and piston area, and vacuum, without making any deduction for friction or hurtful resistances. The steam pressure is in accurate work deduced from indicator diagrams.

Horse Power, Hour. A horse power exerted for one hour, or the equivalent thereof. As the horse power is a unit of activity, the horse power hour is a unit of work or of energy. It is equal to 1,980,000 foot pounds.

H. P. Abbreviation for "horse power."

291 STANDARD ELECTRICAL DICTIONARY.

Hughes' Electro-magnet. A horseshoe electro-magnet with polarized core. It is made by mounting two bobbins of insulated wire on the ends of a permanent horseshoe magnet. It was devised for use in Hughes' printing telegraph, where very quick action is required. The contact lasts only .053 second, 185 letters being transmitted per minute.

Fig. 197 HUGHES' ELECTRO-MAGNET.

Fig. 198. HUGHES' INDUCTION BALANCE.

Hughes' Induction Balance. An apparatus for determining the presence of a concealed mass of metal. The apparatus is variously connected. The cut shows a representative form; a and a' are two primary coils, each consisting of 100 meters (328 feet) of No. 32 silk covered copper wire (0.009 inch diameter) wound on a boxwood spool ten inches in depth; b and b' are secondary coils. All coils are supposed to be alike. The primary coils are joined in series with a battery of three or four Daniell cells. A microphone m is included in the same circuit. The secondary coils are joined in series with a telephone and in opposition with each other. The clock is used to produce a sound affecting the microphone. If all is exactly balanced there will be no sound produced in the telephone. This balance is brought about by slightly varying the distance of one of the secondaries from the primary, until there is no sound in the telephone. If now a piece of metal is placed within either of the coils, it disturbs the balance and the telephone sounds.

292 STANDARD ELECTRICAL DICTIONARY.

To measure the forces acting a sonometer or audiometer is used. This is shown in the upper part of the cut. Two fixed coils, c and e are mounted at the ends of a graduated bar. A movable coil d is connected in the telephone circuit; c and e by a switch can be connected with the battery and microphone circuit, leaving out the induction balance coils. The ends of the coils c and e, facing each other are of the same polarity. If these coils, c and e, were equal in all respects, no sound would be produced when d was midway between them. But they are so wound that the zero position for d is very near one of them, c.

Assume that a balance has been obtained in the induction balance with the coil d at zero. No sound is heard whether the switch is moved to throw the current into one or the other circuit. A piece of metal placed in one of the balance coils will cause the production of a sound. The current is turned into the sonometer and d is moved until the same sound, as tested by rapid movements of the switch, is heard in both circuits. The displacement of d gives the value of the sound.

A milligram of copper is enough to produce a loud sound. Two coins can be balanced against each other, and by rubbing one of them, or by breathing on one of them, the balance will be disturbed and a sound will be produced.

Prof. Hughes has also dispensed with the audiometer. He has used a strip of zinc tapering from a width of 4 mm. (.16 inch) at one end to a sharp edge or point at the other. The piece to be tested being in place in one coil, the strip is moved across the face of the other until a balance is obtained.

As possible uses the detection of counterfeit coins, the testing of metals for similarity of composition and the location of bullets in the body have been suggested. Care has to be taken that no masses of metal interfere. Thus in tests of the person of a wounded man, the presence of an iron truss, or of metallic bed springs may invalidate all conclusions.

The same principle is carried out in an apparatus in which the parts are arranged like the members of a Wheatstone bridge. One pair of coils is used, which react on each other as primary and secondary coils. One of the coils is in series with a telephone in the member of the bridge corresponding to that containing the galvanometer of the Wheatstone bridge. The latter is more properly termed an induction bridge.

Synonyms--Inductance Bridge--Inductance Balance--Induction Bridge.

293 STANDARD ELECTRICAL DICTIONARY.

Hydro-electric. adj. (a) A current produced by a voltaic couple or the couple itself is sometimes thus characterized or designated as a "hydro-electric current" or a "hydro-electric couple." It distinguishes them from thermo-electric.

(b) Armstrong's steam boiler electric machine (see Hydroelectric Machine) is also termed a hydro-electric machine.

Hydro-electric Machine. An apparatus for generating high potential difference by the escape of steam through proper nozzles.

It consists of a boiler mounted on four glass legs or otherwise insulated. An escape pipe terminates in a series of outlets so shaped as to impede the escape of the steam by forcing it out of the direct course. These jets are lined with hard wood. They are enclosed in or led through a box which is filled with cold water.

Fig. 199. ARMSTRONG'S HYDRO-ELECTRIC MACHINE.

This is to partly condense the steam so as to get it into the vesicular state, which is found essential to its action. Dry steam produces no excitation. If the boiler is fired and the steam is permitted to escape under the above conditions the vesicles presumably, or the "steam" is found to be electrified. A collecting comb held against the jet becomes charged and charges any connected surface.

294 STANDARD ELECTRICAL DICTIONARY.

The boiler in the above case is negatively and the escaping "steam" is positively charged. By changing the material of the linings of the jets, or by adding turpentine the sign of the electricity is reversed. If the water contains acid or salts no electricity is produced. The regular hydro-electric machine is due to Sir William Armstrong.

Faraday obtained similar results with moist air currents.

Hydrogen. An element existing under all except the most extreme artificial conditions of pressure and cold as a gas. It is the lightest of known substances. Atomic weight, 1; molecular weight, 2; equivalent, 1; valency, 1; specific gravity, .0691-.0695. (Dumas & Boussingault.)

It is a dielectric of about the same resistance as air. Its specific inductive capacity at atmospheric pressure is: .9997 (Baltzman) .9998 (Ayrton)

Electro-chemical equivalent, .0105 milligram. The above is usually taken as correct. Other values are as follows: .010521 (Kohllrausch) .010415 (Mascart)

The electro-chemical equivalent of any element is obtained by multiplying its equivalent by the electro-chemical equivalent of hydrogen. The value .0105 has been used throughout this book.

Hygrometer. An instrument for determining the moisture in the air. One form consists of a pair of thermometers, one of which has its bulb wrapped in cloth which is kept moist during the observation. The evaporation is more or less rapid according to the dryness or moisture of the air, and as the temperature varies with this evaporation the relative readings of the two thermometers give the basis for calculating the hygrometric state of the air. Another form determines the temperature at which dew is deposited on a silver surface, whence the calculations are made.

Hysteresis, Magnetic. A phenomenon of magnetization of iron. It may be attributed to a sort of internal or molecular friction, causing energy to be absorbed when iron is magnetized. Whenever therefore the polarity or direction of magnetization of a mass of iron is rapidly changed a considerable expenditure of energy is required. It is attributed to the work done in bringing the molecules into the position of polarity.

295 STANDARD ELECTRICAL DICTIONARY.

The electric energy lost by hysteresis may be reduced by vibrations or jarring imparted to the iron, thus virtually substituting mechanical for electrical work.

On account of hysteresis the induced magnetization of a piece of iron or steel for fields of low intensity will depend on the manner in which the material has been already magnetized. Let the intensity of field increase, the magnetization increasing also; then lower the intensity; the substance tends to and does retain some of its magnetism. Then on again strengthening the field it will have something to build on, so that when it attains its former intensity the magnetization will exceed its former value. For a moderate value of intensity of field the magnetization can have many values within certain limits.

Synonym--Hysteresis--Hysteresis, Static--Magnetic Friction.

Hysteresis, Viscous. The gradual increase or creeping up of magnetization when a magnetic force is applied with absolute steadiness to a piece of iron. It may last for half an hour or more and amount to several per cent. of the total magnetization. It is a true magnetic lag.

I. A symbol sometimes used to indicate current intensity. Thus Ohm's law is often expressed I = E/R, meaning current intensity is equal to electro-motive force divided by resistance. C is the more general symbol for current intensity.

Ideoelectrics or Idioelectrics. Bodies which become electric by friction. This was the old definition, the term originating with Gilbert. It was based on a misconception, as insulation is all that is requisite for frictional electrification, metals being thus electrified if held by insulating handles. The term is virtually obsolete; as far as it means anything it means insulating substances such as scaling wax, sulphur, or glass.

Idle Coils. Coils in a dynamo, in which coils no electro-motive force is being generated. This may occur when, as a coil breaks connection with the commutator brush, it enters a region void of lines of magnetic force, or where the lines are tangential to the circle of the armature.

Idiostatic Method. A method of using the absolute or attracted disc electrometer. (See Electrometer, Absolute.) The suspended disc and guard ring are kept at the same potential, which is that of one of the points whose potential difference is to be determined; the lower fixed disc is connected to the other of the points whose potential difference is to be determined. Then we have the formula

V = d * SquareRoot( 8 * PI * F ) / S

in which d is the distance between the discs, V is the difference of potential of the two points, F the force of attraction between the discs in dynes, and S the area of the suspended disc. (See Heterostatic Method.)

296 STANDARD ELECTRICAL DICTIONARY.

Idle Poles. Poles of wire sealed into Crookes' tubes, not used for the discharge connections, but for experimental connections to test the effect of different excitation on the discharge.

Idle Wire. In a dynamo the wire which plays no part in generating electro-motive force. In a Gramme ring the wire on the inside of the ring is idle wire.

Igniter. In arc lamps with fixed parallel carbons of the Jablochkoff type (see Candle, Jablochkoff) a strip of carbon connects the ends of the carbons in the unused candle. This is necessary to start the current. Such strip is called an igniter. It burns away in a very short time when an arc forms producing the light, and lasts, if all goes well, until the candle burns down to its end. Without the igniter the current would not start and no arc would form.

I. H. P. Symbol for indicated horse-power.

Illuminating Power. The relative light given by any source compared with a standard light, and stated in terms of the same, as a burner giving an illuminating power of sixteen candles. For standards see Candle, Carcel--Methven Standard--Pentane Standard.

Illuminating Power, Spherical. The illuminating power of a lamp or source of light may vary in different directions, as in the case of a gas burner or incandescent lamp. The average illuminating power determined by photometric test or by calculation in all directions from the source of light is called the spherical illuminating power, or if stated in candles is called the spherical candle power.

Illumination, Unit of. An absolute standard of light received by a surface. Preece proposed as such the light received from a standard candle (see Candle, Standard) at a distance of 12.7 inches. The object of selecting this distance was to make it equal to the Carcel Standard (see Carcel), which is the light given by a Carcel lamp at a distance of one meter.

From one-tenth to one-fiftieth this degree of illumination was found in gas-lighted streets by Preece, depending on the proximity of the gas lamps.

Image, Electric. An electrified point or system of points on one side of a surface which would produce on the other side of that surface the same electrical action which the actual electrification of that surface really does produce. (Maxwell.)

The method of investigating the distribution of electricity by electric images is due to Sir William Thomson. The conception is purely a theoretical one, and is of mathematical value and interest.

297 STANDARD ELECTRICAL DICTIONARY.

Impedance. The ratio of any impressed electro-motive force to the current which it produces in a conductor. For steady currents it is only the resistance. For variable currents it may include besides resistance inductance and permittance. It is the sum of all factors opposing a current, both ohmic and spurious resistances. It is often determined and expressed as ohms.

Synonym--Apparent Resistance--Virtual Resistance.

Impedance, Oscillatory. The counter-electro-motive force offered to an oscillatory discharge, as that of a Leyden jar. It varies with the frequency of the discharge current.

Synonym--Impulsive Impedance.

Impressed Electro-motive Force. The electro-motive force expending itself in producing current induction in a neighboring circuit.

Impulse. (a) An electro-magnetic impulse is the impulse produced upon the luminiferous ether by an oscillatory discharge or other varying type of current; the impulse is supposed to be identical, except as regards wave-length, with a light wave.

(b) An electro-motive impulse is the electro-motive force which rises so high as to produce an impulsive or oscillatory discharge, such as that of a Leyden jar.

Incandescence, Electric. The heating or a conductor to red, or, more etymologically, to white heat by the passage of an electric current. The practical conditions are a high intensity of current and a low degree of conductance of the conductor relatively speaking.

Inclination Map. A map showing the locus of equal inclination or dips of the magnetic needle. The map shows a series of lines, each one of which follows the places at which the dip of the magnetic needle is identical. The map changes from year to year. (See Magnetic Elements.)

Independence of Currents in Parallel Circuits. If a number of parallel circuits of comparatively high resistance are supplied by a single generator of comparatively low resistance, the current passed through each one will be almost the same whether a single one or all are connected. Under the conditions named the currents are practically independent of each other.

[Transcriber's note: The current in each parallel branch depends on the resistance/impedance of that branch. Only if they all have the same impedance will the current be the same.]

Indicating Bell. An electric bell arranged to drop a shutter or disclose in some other way a designating number or character when rung.

298 STANDARD ELECTRICAL DICTIONARY.

Indicator. (a) An apparatus for indicating the condition of a distant element, such as the water level in a reservoir, the temperature of a drying room or cold storage room or any other datum. They are of the most varied constructions.

(b) The receiving instrument in a telegraph system is sometimes thus termed.

Indicator, Circuit. A galvanometer used to show when a circuit is active, and to give an approximate measurement of its strength. It is a less accurate and delicate form of instrument than the laboratory appliance.

Inductance. The property of a circuit in virtue of which it exercises induction and develops lines of force. It is defined variously. As clear and satisfactory a definition as any is the following, due to Sumpner and Fleming: Inductance is the ratio between the total induction through a circuit to the current producing it. "Thus taking a simple helix of five turns carrying a current of two units, and assuming that 1,000 lines of force passed through the central turn, of which owing to leakage only 900 thread the next adjacent on each side, and again only 800 through the end turns, there would be 800 + 900 + 1000 + 900 + 800, or 4,400 linkages of lines with the wire, and this being with 2 units of current, there would be 2,200 linkages with unit current, and consequently the self-inductance of the helix would be 2,200 centimetres." (Kennelly.) Inductance, as regards its dimensions is usually reduced to a length, hence the last word of the preceding quotation.

The practical unit of inductance is termed the henry, from Prof. Joseph Henry; the secohm, or the quad or quadrant. The latter alludes to the quadrant of the earth, the value in length of the unit in question.

[Transcriber's note: (L (di/dt) = V). A current changing at the rate of one ampere per second through a one henry inductance produces one volt. A sinusoidal current produces a voltage 90 degrees ahead of the current, a cosine (the derivative of sine is cosine). One volt across one henry causes the current to increase at one ampere per second.]

Induction, Coefficient of Self. The coefficient of self-induction of a circuit is the quantity of induction passing through it per unit current in it. If a given circuit is carrying a varying current it is producing a varying quantity of magnetic induction through itself. The quantity of induction through the circuit due to its current is generally proportional to its current. The quantity for unit current is the coefficient of self-induction. (Emtage.)

Induction, Cross. The induction of magnetic lines of force in a dynamo armature core by the current passing around such armature. These lines in a symmetrical two pole machine are at right angles to the lines of force which would normally extend across the space between the two magnet poles. The joint magnetizing effect of the field and of the cross induction produces a distorted field between the poles .

Synonym--Cross-magnetizing Effect.

299 STANDARD ELECTRICAL DICTIONARY.

Induction, Electro-magnetic. The inter-reaction of electromagnetic lines of force with the production of currents thereby.

A current passing through a conductor establishes around it a field of force representing a series of circular lines of force concentric with the axis of the conductor and perpendicular thereto. These lines of force have attributed to them, as a representative of their polarity, direction. This is of course purely conventional. If one is supposed to be looking at the end of a section of conductor, assuming a current be passing through it towards the observer, the lines of force will have a direction opposite to the motion of the hands of a watch. The idea of direction may be referred to a magnet. In it the lines of force are assumed to go from the north pole through the air or other surrounding dielectric to the south pole.

Two parallel wires having currents passing through them in the same direction will attract each other. This is because the oppositely directed segments of lines of force between the conductors destroy each other, and the resultant of the two circles is an approximation to an ellipse. As lines of force tend to be as short as possible the conductors tend to approach each other to make the ellipse become of as small area as possible, in other words to become a circle.

If on the other hand the currents in the conductors are in opposite directions the segments of the lines of force between them will have similar directions, will, as it were, crowd the intervening ether and the wires will be repelled.

Fig. 200. ATTRACTION OF CONDUCTORS CARRYING SIMILAR CURRENTS.

By Ampére's theory of magnetism, (see Magnetism, Ampére's Theory of,) a magnet is assumed to be encircled by currents moving in the direction opposite to that of the hands of a watch as the observer faces the north pole. A magnet near a wire tends to place the Ampérian currents parallel to the wire, and so that the portion of the Ampérian currents nearest thereto will correspond in direction with the current in the wire.

300 STANDARD ELECTRICAL DICTIONARY.

This is the principle of the galvanometer. A number of methods of memoria technica have been proposed to remember it by.

Thus if we imagine a person swimming with the current and always facing the axis of the conductor, a magnetic needle held where the person is supposed to be will have its north pole deflected to the right hand of the person.

Fig. 201. REPULSION OF CONDUCTORS CARRYING OPPOSITE CURRENTS.

Again if we think of a corkscrew, which as it is turned screws itself along with the current, the motion of the handle shows the direction of the lines of force and the direction in which the north pole of a needle is deflected. This much is perhaps more properly electro-dynamics, but is necessary as a basis for the expression of induction.

If a current is varied in intensity in one conductor it will induce a temporary current in another conductor, part of which is parallel to the inducing current and which conductor is closed so as to form a circuit. If the inducing current is decreased the induced current in the near and parallel portion of the other circuit will be of identical direction; if increased the induced current will be of opposite direction.

This is easiest figured by thinking of the lines of force surrounding the inducing conductor. If the current is decreased these can be imagined as receiving a twist or turn contrary to their normal direction, as thereby establishing a turn or twist in the ether surrounding the other wire corresponding in direction with the direction of the original lines of force, or what is the same thing, opposite in direction to the original twist. But we may assume that the establishment of such a disturbance causes a current, which must be governed in direction with the requirements of the new lines of force.

The same reasoning applies to the opposite case.

301 STANDARD ELECTRICAL DICTIONARY.

The general statement of a variable current acting on a neighboring circuit also applies to the approach or recession of an unvarying current, and to the cutting of lines of force by a conductor at right angles thereto. For it is evident that the case of a varying current is the case of a varying number of lines of force cutting or being cut by the neighboring conductor. As lines of force always imply a current, they always imply a direction of such current. The cutting of any lines of force by a closed conductor always implies a change of position with reference to all portions of such conductor and to the current and consequently an induced current or currents in one or the other direction in the moving conductor.

As the inducing of a current represents energy abstracted from that of the inducing circuit, the direction of the induced current is determined by (Lenz's Law) the rule that the new current will increase already existing resistances or develop new ones to the disturbance of the inducing field.

In saying that a conductor cutting lines of force at right angles to itself has a current induced in it, it must be understood that if not at right angles the right angle component of the direction of the wire acts in generating the current. The case resolves itself into the number of lines of force cut at any angle by the moving wire.

The lines of force may be produced by a magnet, permanent or electro. This introduces no new element. The magnet may be referred, as regards direction of its lines of force, to its encircling currents, actual or Ampérian, and the application of the laws just cited will cover all cases.

Induction, Coefficient of Mutual. The coefficient of mutual induction of two circuits is the quantity of magnetic induction passing through either of them per unit current in the other. (Emtage.) It is also defined as the work which must be done on either circuit, against the action of unit current in each, to take it away from its given position to an infinite distance from the other; and also as the work which would be done by either circuit on the other in consequence of unit current in each, as the other moves from an infinite distance to its given position with respect to the other conductor. It depends on the form, size, and relative position of the two circuits; and on the magnetic susceptibilities of neighboring substances.

The ether surrounding two circuits of intensity i' and i" must possess energy, expressible (Maxwell) as 1/2 L i2 + M i i + 1/2 N i12. It can be shown that M i i1 in any given position of the two circuits is numerically equal (1) to the mutual potential energy of the two circuits (2) to the number of lines of induction, which being due to A, pass from A through B, or equally being due to B, pass from B through A, and M is styled the coefficient of mutual induction. (Daniell.)

302 STANDARD ELECTRICAL DICTIONARY.

Induction, Electrostatic. An electrostatic charge has always an opposite and bound charge. This may be so distributed as not to be distinguishable, in which case the charge is termed, incorrectly but conventionally, a free charge. But when a charge is produced an opposite and equal one always is formed, which is the bound charge. The region between the two charges and permeated by their lines of force, often curving out so as to embrace a volume of cross-sectional area larger than the mean facing area of the excited surfaces, is an electrostatic field of force. The establishing of an electrostatic field, and the production of a bound charge are electrostatic induction.

An insulated conductor brought into such a field suffers a redistribution of its electricity, or undergoes electrostatic induction. The parts nearest respectively, the two loci of the original and the bound charges, are excited oppositely to such charges. The conductor presents two new bound charges, one referred to the original charge, the other to the first bound charge.

Induction, Horizontal. In an iron or steel ship the induction exercised upon the compass needle by the horizontal members of the structure, such as deck-beams, when they are polarized by the earth's magnetic induction. This induction disappears four times in swinging a ship through a circle; deviation due to it is termed quadrantal deviation. (See Deviation, Quadrantal.)

Induction, Lateral. A term formerly used to express the phenomenon of the alternative discharge of a Leyden jar or other oscillatory discharge of electricity. (See Discharge, Alternative.)

Induction, Magnetic. The magnetization of iron or other paramagnetic substance by a magnetic field.

On account of its permeability or multiplying power for lines of force, a paramagnetic body always concentrates lines of force in itself if placed in a magnetic field, and hence becomes for the time being a magnet, or is said to be polarized.

As the tendency of lines of force is to follow the most permeable path, a paramagnetic bar places itself lengthwise or parallel with the prevailing direction of the lines of force so as to carry them as far on their way as possible. Every other position of the bar is one of unstable equilibrium or of no equilibrium. The end of the bar where the lines of force enter (see Lines of Force) is a south pole and is attracted towards the north pole of the magnet.

The production of magnetic poles under these conditions in the bar is shown by throwing iron filings upon it. They adhere to both ends but not to the middle.

Induction, Mutual, Electro-magnetic. The induction due to two electric currents reacting on each other.

303 STANDARD ELECTRICAL DICTIONARY.

Induction, Mutual, Electrostatic. A charged body always induces a charge upon any other body near it; and the same charge in the second body will induce the other charge in the first body if the latter is unexcited. In other words the second body's induction from the first is the measure of the charge the second would require to induce in the first its own (the second's) induced charge. This is the law of mutual electrostatic induction.

Induction, Open Circuit. Inductive effects produced in open circuits. By oscillatory discharges a discharge can be produced across a break in a circuit otherwise complete. The requirements for its production involve a correspondence or relation of its dimensions to the inducing discharge. The whole is analogous to the phenomena of sound resonators and sympathetic vibrations. Synonym--Oscillatory induction.

Induction, Self-. (a) A phenomenon of electric currents analogous to the inertia of matter. Just as water which fills a pipe would resist a sudden change in its rate of motion, whether to start from rest, to cease or decrease its motion, so an electric current requires an appreciable time to start and stop. It is produced most strongly in a coiled conductor, especially if a core of iron is contained within it.

As in the case of two parallel wires, one bearing currents which vary, momentary currents are induced in the other wire, so in a single conductor a species of inertia is found which retards and prolongs the current. If a single conductor is twisted into a helix or corresponding shape, its separate turns react one on the other in accordance with the general principles of electromagnetic induction. (See Induction, Electro-magnetic.) Thus when a current is suddenly formed the coils acting upon each other retard for an instant its passage, producing the effect of a reverse induced current or extra current opposing the principal current. Of course no extra current is perceptible, but only the diminution. When the current is passing regularly and the current is broken, the corresponding action prolongs the current or rather intensifies it for an instant, producing the true extra current. This is current self-induction.

[Transcriber's note: See inductance.]

Synonyms--Electric Inertia--Electro-dynamic Capacity.

(b) A permanent magnet is said to tend to repel its own magnetism, and thus to weaken itself; the tendency is due to magnetic self-induction.

Induction Sheath. In the brush dynamo a thin sheet of copper surrounding the magnet cores with edges soldered together. The winding is outside of it. Its object is to absorb extra currents set up by variations in magnetic intensity in the cores. These currents otherwise would circulate in the cores.

304 STANDARD ELECTRICAL DICTIONARY.

Induction, Unit of Self-. The unit of self-induction is the same as that of induction in general. It is the henry, q. v.

Induction, Unipolar. Induction produced in a conductor which continuously cuts the lines of force issuing from one pole of a magnet. As the lines of force are always cut in the same sense a continuous and constant direction current is produced.

Induction, Vertical. In an iron or steel ship the induction or attraction exercised in the compass by vertical elements of the structure. Such vertical masses of iron in the northern hemisphere would have their upper ends polarized as south poles, and would affect the magnet as soon as the vessel swung out of the magnetic meridian. Thus this induction disappears twice in swinging a ship through a complete circle; deviation due to it is termed semi-circular deviation. (See Deviation, Semi-circular.)

Fig. 202. INDUCTOR DYNAMO.

Inductophone. A method of train telegraphy. The train carries a circuit including a coil, and messages are picked up by it from coils along the line into which an alternating current is passed. A telephone is used as a receiver in place of a sounder or relay. The invention, never practically used, is due to Willoughby Smith.

305 STANDARD ELECTRICAL DICTIONARY.

Inductor. (a) In a current generator a mass of iron, generally laminated, which is moved past a magnet pole to increase the number of lines of force issuing therefrom. It is used in inductor dynamos. (See Dynamo Inductor.) In the cut Fig. 202, of an inductor dynamo i, i, are the laminated inductors.

(b) In influence machines the paper or tinfoil armatures on which the electrification is induced.

Inertia. A force in virtue of which every body persists in its state of motion or rest except so far as it is acted on by some force.

Inertia, Electro-magnetic. This term is sometimes applied to the phenomena of self-induction, or rather to the cause of these phenomena.

Infinity Plug. A plug in a resistance box, which on being pulled out of its seat opens the circuit or makes it of infinite resistance. The plug seats itself between two brass plates which are not connected with each other in any way. The other plates are connected by resistance coils of varying resistance.

Influence, Electric. Electric induction, which may be either electrostatic, current, or electro-magnetic.

Insolation, Electric. Exposure to powerful arc-light produces effects resembling those of sun-stroke. The above term or the term "electric sun-stroke" has been applied to them.

[Transcriber's note: Operators of arc welders are prone to skin cancer from ultra violet rays if not properly protected.]

Installation. The entire apparatus, buildings and appurtenances of a technical or manufacturing establishment. An electric light installation, for instance, would include the generating plant, any special buildings, the mains and lamps.

Insulating Stool. A support for a person, used in experiments with static generators. It has ordinarily a wooden top and glass legs. It separates one standing on it from the earth and enables his surface to receive an electrostatic charge. This tends to make his hair stand on end, and anyone on the floor who touches him will receive a shock.

Insulating Tape. Prepared tape used in covering the ends of wire where stripped for making joints. After the stripped ends of two pieces are twisted together, and if necessary soldered and carefully cleaned of soldering fluid, they may be insulated by being wound with insulating tape.

The tape is variously prepared. It may be common cotton or other tape saturated with any insulating compound, or may be a strip of gutta percha or of some flexible cement-like composition.

306 STANDARD ELECTRICAL DICTIONARY.

Insulating Varnish. Varnish used to coat the surface of glass electrical apparatus, to prevent the deposition of hygrometric moisture, and also in the construction of magnetizing and induction coils and the like. Shellac dissolved in alcohol is much used. Gum copal dissolved in ether is another. A solution of sealing wax in alcohol is also used. If applied in quantities these may need baking to bring about the last drying. (See Shellac Varnish.)

Insulator. (a) Any insulating substance.

(b) A telegraph or line insulator for telegraph wires. (See Insulator, Line or Telegraph.)

Synonyms--Dielectric--Non-conductor.

Insulator Cap. A covering or hood, generally of iron, placed over an insulator to protect it from injury by fracture with stones or missiles.

Insulator, Fluid. (a) For very high potentials, as in induction coils or alternating circuits, fluid insulators, such as petroleum or resin oil, have been used. Their principal merit is that if a discharge does take place through them the opening at once closes, so that they are self-healing.

(b) Also a form of telegraph or line insulator in which the lower rim is turned up and inwards, so as to form an annular cup which is filled with oil.

Insulator, Line or Telegraph. A support often in the shape of a collar or cap, for a telegraph or other wire, made of insulating material. Glass is generally used in the United States, porcelain is adopted for special cases; pottery or stone ware insulators have been used a great deal in other countries. Sometimes the insulator is an iron hook set into a glass screw, which is inserted into a hole in a telegraph bracket. Sometimes a hook is caused to depend from the interior of an inverted cup and the space between the shank of the hook and cup is filled with paraffine run in while melted.

Insulators are tested by measuring their resistance while immersed in a vessel of water.

Intensity. Strength. The intensity of a current or its amperage or strength; the intensity or strength of a magnetic field or its magnetic density; the intensity or strength of a light are examples of its use. In the case of dynamic electricity it must be distinguished from tension. The latter corresponds to potential difference or voltage and is not an attribute of current; intensity has no reference to potential and is a characteristic of current.

Intensity of a Magnetic Field. The intensity of a magnetic field at any point is measured by the force with which it acts on a unit magnet pole placed at that point. Hence unit intensity of field is that intensity of field which acts on a unit pole with a force of one dyne. (S. P. Thomson.) (See Magnetic Lines of Force.)

307 STANDARD ELECTRICAL DICTIONARY.

Intercrossing. Crossing a pair of conductors of a metallic circuit from side to side to avoid induction from outside sources.

Intermittent. Acting at intervals, as an intermittent contact, earth, or grounding of a telegraph wire.

Interpolar Conductor. A conductor connecting the two poles of a battery or current generator; the external circuit in a galvanic circuit.

Interpolation. A process used in getting a closer approximation to the truth from two varying observations, as of a galvanometer. The process varies for different cases, but amounts to determining an average or deducing a proportional reading from the discrepant observed ones.

Interrupter. A circuit breaker. It may be operated by hand or be automatic. (See Circuit Breaker--Circuit Breaker, Automatic--and others.)

Interrupter, Electro-magnetic, for a Tuning Fork. An apparatus for interrupting a current which passes through an electromagnet near and facing one of the limbs of a tuning fork. The circuit is made and broken by the vibrations of another tuning fork through which the current passes. The second one is thus made to vibrate, although it may be very far off and may not be in exact unison with the first. The first tuning fork has a contact point on one of its limbs, to close the circuit; it may be one which dips into a mercury cup.

Intrapolar Region. A term in medical electricity, denoting the part of a nerve through which a current is passing.

Ions. The products of decomposition produced in any given electrolysis are termed ions, the one which appears at the anode or negative electrode is the anion. The electrode connected to the carbon or copper plate of a wet battery is an anode. Thus in the electrolysis of water oxygen is the anion and hydrogen is termed the kation. In this case both anion and kation are elements. In the decomposition of copper sulphate the anion is properly speaking sulphion (S O4), a radical, and the kation is copper, an element. Electro-negative elements or radicals are anions, such as oxygen, sulphion, etc., while electro-positive ones are kations, such as potassium. Again one substance may be an anion referred to one below it and a kation referred to one above it, in the electro-chemical series, q. v. Anion means the ion which goes to the anode or positive electrode; kation, the ion which goes to the kathode or negative electrode.

[Transcriber's note: An ion is an atom or molecule that has lost or gained one or more valence electrons, giving it a positive or negative electrical charge. A negatively charged ion, with more electrons than protons in its nuclei, is an anion. A positively charged ion, with fewer electrons than protons, is a cation. The electron was discovered five years after this publication.]

308 STANDARD ELECTRICAL DICTIONARY.

Iron. A metal; one of the elements; symbol, Fe; atomic weight, 56; equivalent, 28 and 14, ; valency, 4 and 2. It is a conductor of electricity. The following data are at 0° C. 32° F., with annealed metal.

Specific Resistance, 9.716 microhms. Relative Resistance. 6.460 Resistance of a wire, (a) 1 foot long weighing 1 grain, 1.085 ohms. (b) 1 foot long 1/1000 inch thick, 58.45 " (c) 1 meter long weighing 1 gram, .7570 " (d) 1 meter long, 1 millimeter thick, .1237 " Percentage increase in resistance per degree C. (1.8° F.) at about 20° C. (68°F.), about 0.5 per cent. Resistance of a 1 inch cube, 3.825 microhms. Electro-chemical equivalent (Hydrogen = .0105), .147 and .294

Iron, Electrolytic. Iron deposited by electrolytic action. Various baths are employed for its formation. (See Steeling.) It has very low coercive power, only seven to ten times that of nickel.

Ironwork Fault of a Dynamo. A short circuiting of a dynamo by, or any connection of its coils with, the iron magnet cores or other iron parts.

Isochronism. Equality of periodic time; as of the times of successive beats of a tuning fork, or of the times of oscillations of a pendulum.

Isoclinic Lines. The lines denoting the locus of sets of equal dips or inclinations of the magnetic needle upon the earth's surface, the magnetic parallels, q. v. These lines are very irregular. (See Magnetic Elements.)

Isoclinic Map. A map showing the position of isoclinic lines.

Isodynamic Lines. Lines marking the locus of places of equal magnetic intensity on the earth's surface. (See Magnetic Elements, Poles of Intensity.)

Isodynamic Map. A map showing the position of isodynamic lines. (See Poles of Intensity.)

Isogonic Lines. Lines on a map marking the locus of or connecting those points where the declination or variation of the magnetic needle is the same. (See Magnetic Elements--Declination of Magnetic Needle.)

Synonyms--Isogonal Lines--Halleyan Lines.

309 STANDARD ELECTRICAL DICTIONARY.

Isogonic Map. A map showing the isogonic lines. On such a map each line is characterized and marked with the degrees and direction of variation of the compass upon itself.

Synonym--Declination Map.

Isolated Plant, Distribution or Supply. The system of supplying electric energy by independent generating systems, dynamo or battery, for each house, factory or other place, as contra-distinguished from Central Station Distribution or Supply.

Isotropic. (Greek, equal in manner.)

Having equal properties in all directions; the reverse of anisotropic, q. v. Thus a homogeneous mass of copper or silver has the same specific resistance in all directions and is an isotropic conductor. Glass has the same specific inductive capacity in all directions and is an isotropic medium or dielectric. The same applies to magnetism. Iron is an isotropic paramagnetic substance. (See Anisotropic.) The term applies to other branches of physics also.

I. W. G. Contraction for Indian Wire Gauge--the gauge adopted in British India.

J. Symbol for the unit joule, the unit of electric energy.

Jacobi's Law. A law of electric motors. It states that the maximum work of a motor is performed when the counter-electromotive force is equal to one-half the electro-motive force expended on the motor.

Jewelry. Small incandescent lamps are sometimes mounted as articles of jewelry in scarf-pins or in the hair. They may be supplied with current from storage or from portable batteries carried on the person.

Joint, American Twist. A joint for connecting telegraph wires, especially aerial lines. Its construction is shown in the cut. The end of each wire is closely wound around the straight portion of the other wire for a few turns.

Fig. 203. AMERICAN TWIST JOINT.

310 STANDARD ELECTRICAL DICTIONARY.

Joint, Britannia. A joint for uniting the ends of telegraph and electric wires. The ends of the wires are scraped clean and laid alongside each other for two inches, the extreme ends being bent up at about right angles to the wire. A thin wire is wound four or five times around one of the wires, back of the joint, the winding is then continued over the lapped portion, and a few more turns are taken around the other single wire. The whole is then soldered.

Fig. 204. BRITANNIA JOINT.

Joint, Butt. A joint in belting or in wire in which the ends to be joined are cut off square across, placed in contact and secured. It ensures even running when used in belting. Any irregularity in thickness of a belt affects the speed of the driven pulley. As dynamos are generally driven by belts, and it is important to drive them at an even speed to prevent variations in the electro-motive force, butt joints should be used on belting for them, unless a very perfect lap joint is made, which does not affect either the thickness or the stiffness of the belt.

When a butt joint is used in wire a sleeve may be used to receive the abutting ends, which may be secured therein by soldering. This species of joint has been used on lightning rods and may more properly be termed a sleeve joint.

Joint, Lap. (a) In belting a joint in which the ends are overlapped, and riveted or otherwise secured in place. If made without reducing the thickness of the ends it is a bad joint for electrical work, as it prevents even running of machinery to which it is applied. Hence dynamo belts should be joined by butt joints, or if by lap joints the ends should be shaved off so that when joined and riveted, there will be no variation in the thickness of the belt.

(b) In wire lap joints are made by overlapping the ends of the wire and soldering or otherwise securing. The Britannia joint (see Joint, Britannia,) may be considered a lap-joint.

Joint, Marriage. A joint for stranded conductors used for Galende's cables. It is made somewhat like a sailor's long splice. Each one of the strands is wound separately into the place whence the opposite strand is unwound and the ends are cut off so as to abutt. In this way all are smoothly laid in place and soldering is next applied.

Fig. 205. MARRIAGE JOINT.

311 STANDARD ELECTRICAL DICTIONARY.

Joint, Sleeve. A joint in electric conductors, in which the ends of the wires are inserted into and secured in a metallic sleeve or tube, whose internal diameter is just sufficient to admit them.

Joint, Splayed. The method of joining the ends of stranded conductors. The insulating covering is removed, the wires are opened out, and the center wire, heart or core of the cable is cut off short. The two ends are brought together, the opened out wires are interlaced or crotched like the fingers of the two hands, and the ends are wound around the body of the cable in opposite directions. The joint is trimmed and well soldered. Tinned wire with rosin flux for the soldering is to be recommended. Insulating material is finally applied by hand, with heat if necessary.

Joints in Belts. Belt-joints for electric plants where the belts drive dynamos should be made with special care. The least inequality affects the electro-motive force. Butt joints are, generally speaking, the best, where the ends of the belt are placed in contact and laced. Lap-joints are made by overlapping the belt, and unless the belt is carefully tapered so as to preserve uniform strength, the speed of the dynamo will vary and also the electromotive force.

Joulad. A name proposed to be substituted for "joule," q. v. It has not been adopted.

Joule. This term has been applied to several units.

(a) The practical C. G. S. unit of electric energy and work--the volt-coulomb. It is equal to 1E7 ergs--0.73734 foot pound.--.00134 horse power seconds. A volt-ampere represents one joule per second.

(b) It has also been used as the name of the gram-degree C. thermal unit--the small calorie.

Synonym--Joulad.

Joule Effect. The heating effect of a current passing through a conductor. It varies with the product of the resistance by the square of the current, or with (C^2)*R.

Joule's Equivalent. The mechanical equivalent of heat, which if stated in foot-pounds per pound-degree F. units, is 772 (772.55). (See Equivalents.)

Junction Box. In underground distribution systems, an iron casing or box in which the feeders and mains are joined, and where other junctions are made.

Synonym--Fishing Box.

K. The symbol for electrostatic capacity.

Kaolin. A product of decomposition of feldspar, consisting approximately of silica, 45, alumina, 40, water, 15. It was used in electric candles of the Jablochkoff type as a constituent of the insulating layer or colombin. Later it was abandoned for another substance, as it was found that it melted and acted as a conductor.

312 STANDARD ELECTRICAL DICTIONARY.

Kapp Line of Force. A line of force proposed by Kapp. It is equal to 6,000 C. G. S. lines of force, and the unit of area is the square inch. Unfortunately it has been adopted by many manufacturers, but its use should be discouraged, as it is a departure from the uniform system of units.

One Kapp line per square inch = 930 C. G. S. lines per square centimeter.

Kathelectrotonus. A term used in medical electricity or electro-therapeutics to indicate the increased functional activity induced in a nerve by the proximity of the kathode of an active circuit which is completed through the nerve. The converse of anelectrotonus.

Kathode. The terminal of an electric circuit whence an electrolyzing current passes from a solution. It is the terminal connected to the zinc plate of a primary battery.

Kathodic Closure Contraction. A term in electro-therapeutics; the contractions near where the kathode of an active circuit is applied to the body, which are observed at the instant when the circuit is closed.

Kathodic Duration Contraction. A term in electro-therapeutics; the contraction near where the kathode of an active circuit is applied to the body for a period of time.

K. C. C. Abbreviation for Kathodic Closure Contraction, q. v.

K. D. C. Abbreviation for Kathodic Duration Contraction, q. v.

Keeper. A bar of soft iron used to connect the opposite poles of a horseshoe magnet or the opposite poles of two bar magnets placed side by side. It is designed to prevent loss of magnetism. The armature of a horseshoe magnet is generally used as its keeper. For bar magnets a keeper is used for each end, the magnets being laid side by side, with their poles in opposite direction but not touching, and a keeper laid across at each end connecting the opposite poles.

Kerr Effect. The effect of an electrostatic field upon polarized light traversing a dielectric contained within the field. (See Electrostatic Refraction.)

Kerr's Experiment. Polarized light reflected from the polished face of a magnet pole has its plane of polarization rotated; when it is reflected from the north pole the rotation is from left to right.

313 STANDARD ELECTRICAL DICTIONARY.

Key. A switch adapted for making and breaking contact easily when worked by hand, as a Morse telegraph key.

Key Board. A board or tablet on which keys or switches are mounted.

Key-board. (a) A switch board, q. v.

(b) A set of lettered keys similar to those of a typewriter employed in some telegraph instruments. As each key is depressed it produces the contact or break requisite for the sending of the signal corresponding to the letter marked upon the key. The signal in printing telegraphs, on which such key-boards are used, is the reprinting of the letter at the distant end of the line.

Key, Bridge. A key for use with a Wheatstone Bridge, q.v. It is desirable to first send a current through the four arms of the bridge in using it for testing resistances and then through the galvanometer, because it takes a definite time for the current to reach its full strength. This is especially the case if the element being measured has high static capacity, as a long ocean cable. If the galvanometer connections were completed simultaneously with the bridge connections a momentary swing would be produced even if the arms bore the proper relation to each other. This would cause delay in the testing. A bridge key avoids this by first connecting the battery circuit through the arms of the bridge, and then as it is still further depressed the galvanometer circuit is completed.

314 STANDARD ELECTRICAL DICTIONARY.

Fig. 206. CHARGE AND DISCHARGE KEY

Key, Charge and Discharge. A key for use in observing the discharge of a condenser immediately after removing the battery. In one typical form it has two contacts, one below and one above, and being a spring in itself is pressed up against the upper one. Connections are so made that when in its upper position it brings the two coatings of the condenser in circuit with the galvanometer. When depressed it does the same for a battery. In use it is depressed and suddenly released when the galvanometer receives the full charge, before there has been time for leakage. This is one method of connection illustrating its principle.

In the cut L is the spring-key proper. S2, is the upper contact screw against which the spring normally presses. In this position the galvanometer G is in circuit with the opposite coatings of the condenser C. On depressing the contact S2, is broken and S1, is made. This brings the battery B in circuit with the condenser coatings. On releasing the key it springs up and the galvanometer receives the effect of the charge of the condenser as derived from the battery.

Key, Double Contact. A key arranged to close two distinct circuits, holding the first closed until the second is completed. It is used for Wheatstone bridge work.

Key, Double Tapper. A telegraph key giving contacts alternately for currents in opposite directions, used in needle telegraphy.

Key, Increment. A key for use in duplex and quadruplex telegraphy. Its action is to increase the line current, not merely to suddenly turn current into it.

315 STANDARD ELECTRICAL DICTIONARY.

Fig. 207. KEMPE'S DISCHARGE KEY.

Key, Kempe's Discharge. A key giving a charging, discharging and insulating connection, for static condenser work. Referring to the cut l is a lever or spring with upper discharging contact s, and lower charging contact s'. In use it is pressed down by the insulating handle or finger piece C, until caught by the hook attached to the key I. This hook is lower down than that on the key D, and holds it in contact with the charging contact piece S'. On pressing the key I, marked or designated "Insulate," it springs up, breaks contact at S', and catching against the hook on D, which key is designated "Discharge," remains insulated from both contacts; next on pressing D it is released and springs up and closes the discharge contact S. It is a form of charge and discharge key. (See Key, Charge and Discharge.)

Key, Magneto-electric. A telegraph key whose movements operate what is virtually a small magneto-generator, so as to produce currents of alternating direction, one impulse for each motion of the key. It is employed for telegraphing without a line battery, a polarized relay being used. In one very simple form a key is mounted on a base with a permanent magnet and connected to the armature, so that when the key is pressed downwards it draws the armature away from the poles of the magnet. If the magnet or its armature is wound with insulated wire this action of the key will cause instantaneous currents to go through a circuit connected to the magnet or armature coils.

Fig. 208. SIEMENS' MAGNETO-ELECTRIC KEY.

In Siemens & Halske's key an H armature E is pivoted between the poles N S, of a powerful compound horseshoe magnet, G G. It is wound with fine wire and a key handle H is provided for working it. In its normal position the handle is drawn upward, and the end S S of the armature core is in contact with the south pole S of the permanent magnet, and the end D D with the north pole. This establishes the polarity of the armature. On depressing the key the contacts are broken and in their place the end D D comes in contact with the south pole and the end S S with the north pole. This suddenly reverses the polarity of the armature and sends a momentary current through the armature coil which is in circuit with the line. The cut only shows the principle of the key, whose construction is quite complicated.

316 STANDARD ELECTRICAL DICTIONARY.

Key, Make and Break. An ordinary electric key, usually making a contact when depressed, and rising by spring action when released, and in its rise breaking the contact.

Fig. 209. PLUG KEY

Key, Plug. An appliance for closing a circuit. Two brass blocks are connected to the terminals, but are disconnected from each other. A brass plug slightly coned or with its end split so as to give it spring action is thrust between the blocks to complete the circuit. It is used in Resistance coils and elsewhere. (See Coil, Resistance.) Grooves are formed in the blocks to receive the plug.

Key, Reversing. (a) A double key, arranged so that by depressing one key a current flows in one direction, and by depressing the other a current flows in the opposite direction. It is used in connection with a galvanometer in experimental, testing or measuring operations.

(b) A key effecting the same result used in quadruplex telegraphy.

Key, Sliding-Contact. A name given to the key used for making instantaneous contacts with the metre wire of a metre bridge, q. v. The name is not strictly correct, because it is important that there should be no sliding contact made, as it would wear out the wire and make it of uneven resistance.

It is a key which slides along over the wire and which, when depressed, presses a platinum tipped knife edge upon the wire. On being released from pressure the key handle springs up and takes the knife edge off the wire. This removal is essential to avoid wearing the wire, whose resistance per unit of length must be absolutely uniform.

Key, Telegraph. The key used in telegraphy for sending currents as desired over the line. It consists of a pivoted lever with finger piece, which lever when depressed makes contact between a contact point on its end and a stationary contact point on the base. This closes the circuit through the line. When released it springs up and opens the line circuit.

Kilo. A prefix to the names of units; it indicates one thousand times, as kilogram, one thousand grams. A few such units are given below.

Kilodyne. A compound unit; one thousand dynes. (See Dyne.)

Kilogram. A compound unit; one thousand grams; 2.2046 pounds avds.

317 STANDARD ELECTRICAL DICTIONARY.

Kilojoule. A compound unit; one thousand joules, q. v.

Kilometer. A compound unit; one thousand meters; 3280.899 feet; 0.621382 statute miles. (See Meter.)

Kilowatt. A compound unit; one thousand watts, q. v.

Kine. An absolute or C. G. S. unit of velocity or rate of motion; one centimeter per second; proposed by the British Association.

Kirchoff's Laws. These relate to divided circuits.

I. When a steady current branches, the quantity of electricity arriving by the single wire is equal to the quantity leaving the junction by the branches. The algebraical sum of the intensities of the currents passing towards (or passing from) the junction is equal to zero; Summation(C) = 0 (Daniell.) In the last sentence currents flowing towards the point are considered of one sign and those flowing away from it of the other.

II. In a metallic circuit comprising within it a source of permanent difference of potential, E, the products of the intensity of the current within each part of the circuit into the corresponding resistance are, if the elements of current be all taken in cyclical order together, equal to E; Summation(C * r) =E. In a metallic circuit in which there is no source of permanent difference of potential E = 0, and Summation(C * r) = 0.

This law applies to each several mesh of a wire network as well as to a single metallic loop, and it holds good even when an extraneous current is passed through the loop. (Daniell.)

In this statement of the two laws E stands for electro-motive force, C for current intensity; and r for resistance of a single member of the circuit.

[Transcriber's note: These laws may be restated as: At any point in an steady-state electrical circuit, the directed sum of currents flowing towards that point is zero. The directed sum of the electrical potential differences around any closed circuit is zero.]

Knife-edge Suspension. The suspension of an object on a sharp edge of steel or agate. The knife edge should abut against a plane. The knife edge is generally carried by the poised object. Its edge then faces downward and on the support one or more plane or approximately plane surfaces are provided on which it rests. In the ordinary balance this suspension can be seen. It is sometimes used in the dipping needle.

It is applied in cases where vertical oscillations are to be provided for.

Knot. The geographical mile; a term derived from the knots on the log line, used by navigators. It is equal to 6,087 feet.

Synonyms--Nautical Mile--Geographical Mile.

[Transcriber's note: A knot is a velocity, 1 nautical mile per hour, not a distance. The contemporary definition is: 1 international knot = 1 nautical mile per hour = 1.852 kilometres per hour = 1.1507794 miles per hour = 0.51444444 meters per second = 6076.1152 feet per hour.]

318 STANDARD ELECTRICAL DICTIONARY.

Kohlrausch's Law. A law of the rate of travel of the elements and radicals in solutions under the effects of electrolysis. It states that each element under the effects of electrolysis has a rate of travel for a given liquid, which is independent of the element with which it was combined. The rates of travel are stated for different elements in centimeters per hour for a potential difference of one or more volts per centimeter of path.

[Friedrich Wilhelm Georg Kohlrausch (1840-1910)]

Kookogey's Solution. An acid exciting and depolarizing solution for a zinc-carbon couple, such as a Bunsen battery. Its formula is: Potassium bichromate, 227 parts; water, boiling, 1,134 parts; while boiling add very carefully and slowly 1,558 parts concentrated sulphuric acid. All parts are by weight. Use cold.

Krizik's Cores. Cores of iron for use with magnetizing coils, q. v. They are so shaped, the metal increasing in quantity per unit of length, as the centre is approached, that the pull of the excited coil upon them will as far as possible be equal in all positions. A uniform cylinder is attracted with varying force according to its position; the Krizik bars or cores are attracted approximately uniformly through a considerable range.

L. Symbol for length and also for the unit of inductance or coefficient of induction, because the dimensions of inductance are length.

Lag, Angle of. (a) The angle of displacement of the magnetic axis of an armature of a dynamo, due to its magnetic lag. The axis of magnetism is displaced in the direction of rotation. (See Magnetic Lag.)

(b) The angle expressing the lag of alternating current and electro-motive force phases.

Laminated. adj. Made up of thin plates, as a laminated armature core or converter core.

Lamination. The building up of an armature core or other thing out of plates. The cores of dynamo armatures or of alternating current converters are often laminated. Thus a drum armature core may consist of a quantity of thin iron discs, strung upon a rod and rigidly secured, either with or without paper insulation between the discs. If no paper is used the film of oxide on the iron is relied on for insulation. The object of lamination is to break up the electrical continuity of the core, so as to avoid Foucault currents. (See Currents, Foucault.) The laminations should be at right angles to the direction of the Foucault currents which would be produced, or in most cases should be at right angles to the active parts of the wire windings.

319 STANDARD ELECTRICAL DICTIONARY.

Lamination of Armature Conductors. These are sometimes laminated to prevent the formation of eddy currents. The lamination should be radial, and the strips composing it should be insulated from each other by superficial oxidation, oiling or enamelling, and should be united only at their ends.

Fig. 210. PILSEN ARC LAMP.

Lamp, Arc. A lamp in which the light is produced by a voltaic arc. Carbon electrodes are almost universally employed. Special mechanism, operating partly by spring or gravity and partly by electricity, is employed to regulate the distance apart of the carbons, to let them touch when no current passes, and to separate them when current is first turned on.

The most varied constructions have been employed, examples of which will be found in their places. Lamps may in general be divided into classes as follows, according to their regulating mechanism and other features:

(a) Single light regulators or monophotes. Lamps through whose regulating mechanism the whole current passes. These are only adapted to work singly; if several are placed in series on the same circuit, the action of one regulator interferes with that of the next one.

(b) Multiple light regulators or polyphotes. In these the regulating mechanism and the carbons with their arc are in parallel; the regulating device may be a single magnet or solenoid constituting a derived or shunt-circuit lamp, or it may include two magnets working differentially against or in opposition to each other constituting a differential lamp.

320 STANDARD ELECTRICAL DICTIONARY.

(c) Lamps with fixed parallel carbons termed candles (q. v., of various types).

(d) Lamps without regulating mechanism. These include lamps with converging carbons, whose object was to dispense with the regulating mechanism, but which in some cases have about as much regulating mechanism as any of the ordinary arc lamps.

Lamp, Contact. A lamp depending for its action on loose contact between two carbon electrodes. At the contact a species of incandescence with incipient arcs is produced. One of the electrodes is usually flat or nearly so, and the other one of pencil shape rests upon it.

Lamp, Differential Arc. An arc lamp, the regulation of the distance between whose carbons depends on the differential action of two separate electrical coils. The diagram illustrates the principle. The two carbons are seen in black; the upper one is movable, The current arrives at A. It divides, and the greater part goes through the low resistance coil M to a contact roller r, and thence by the frame to the upper carbon, and through the arc and lower carbon to B, where it leaves the lamp. A smaller portion of the current goes through the coil M1 of higher resistance and leaves the lamp also at B. A double conical iron core is seen, to which the upper carbon holder is attached. This is attracted in opposite directions by the two coils. If the arc grows too long its resistance increases and the coil M1 receiving more current draws it down and thus shortens the arc. If the arc grows too short, its resistance falls, and the coil M receives more current and draws the core upwards, thus lengthening the arc. This differential action of the two cores gives the lamp its name. R is a pulley over which a cord passes, one end attached to the core and the other to a counterpoise weight, W.

Fig. 211. DIAGRAM OF THE PILSEN DIFFERENTIAL ARC LAMP.

321 STANDARD ELECTRICAL DICTIONARY.

Lamp, Holophote. A lamp designed for use alone upon its own circuit. These have the regulating mechanism in series with the carbon and arc, so that the whole current goes through both. (See Lamp, Arc.)

Synonym--Monophote Lamp.

Lamp-hour. A unit of commercial supply of electric energy; the volt-coulombs required to maintain an electric lamp for one hour. A sixteen-candle power incandescent lamp is practically the lamp alluded to, and requires about half an ampere current at 110 volts, making a lamp-hour equal to about 198,000 volt-coulombs.

[Transcriber's note: 0.55 KW hours.]

Lamp, Incandescent. An electric lamp in which the light is produced by heating to whiteness a refractory conductor by the passage of a current of electricity. It is distinguished from an arc lamp (which etymologically is also an incandescent lamp) by the absence of any break in the continuity of its refractory conductor. Many different forms and methods of construction have been tried, but now all have settled into approximately the same type.

The incandescent lamp consists of a small glass bulb, called the lamp-chamber, which is exhausted of air and hermetically sealed. It contains a filament of carbon, bent into a loop of more or less simple shape. This shape prevents any tensile strain upon the loop and also approximates to the outline of a regular flame.

Fig. 212. INCANDESCENT ELECTRIC LAMP.

322 STANDARD ELECTRICAL DICTIONARY.

The loop is attached at its ends to two short pieces of platinum wire, which pass through the glass of the bulb and around which the glass is fused. As platinum has almost exactly the same coefficient of heat-expansion as glass, the wires do not cause the glass to crack.

The process of manufacture includes the preparation of the filament. This is made from paper, silk, bamboo fibre, tamidine, q. v., or other material. After shaping into the form of the filament the material is carbonized at a high heat, while embedded in charcoal, or otherwise protected from the air. The flashing process (see Flashing of incandescent Lamp Carbons) may also be applied. The attachment to the platinum wires is effected by a minute clamp or by electric soldering. The loop is inserted and secured within the open globe, which the glass blower nearly closes, leaving one opening for exhaustion.

The air is pumped out, perhaps first by a piston pump, but always at the end by a mercurial air pump. (See Pump, Geissler--and others.) As the exhaustion becomes high a current is passed through the carbons heating them eventually to white heat so as to expel occluded gas. The occluded gases are exhausted by the pump and the lamp is sealed by melting the glass with a blowpipe or blast-lamp flame. For the exhaustion several lamps are usually fastened together by branching glass tubes, and are sealed off one by one.

The incandescent lamps require about 3.5 watts to the candle power, or give about 12 sixteen-candle lamps to the horse power expended on them.

Generally incandescent lamps are run in parallel or on multiple arc circuits. All that is necessary in such distribution systems is to maintain a proper potential difference between the two leads across which the lamps are connected. In the manufacture of lamps they are brought to an even resistance and the proper voltage at which they should be run is often marked upon them. This may be fifty volts and upward. One hundred and ten volts is a very usual figure. As current one ampere for a fifty-volt, or about one-half an ampere for a one hundred and ten volt lamp is employed.

Lamp, Incandescent, Three Filament. A three filament lamp is used for three phase currents. It has three filaments whose inner ends are connected, and each of which has one leading-in wire. The three wires are connected to the three wires of the circuit. Each filament receives a current varying in intensity, so that there is always one filament passing a current equal to the sum of the currents in the other two filaments.

Lamp, Lighthouse. A special type of arc light. It is adapted for use in a lighthouse dioptric lantern, and hence its arc has to be maintained in the same position, in the focus of the lenses. The lamps are so constructed as to feed both carbons instead of only one, thereby securing the above object.

323 STANDARD ELECTRICAL DICTIONARY.

Lamp, Pilot. A lamp connected to a dynamo, and used by its degree of illumination to show when the dynamo on starting becomes excited, or builds itself up.

Lamp, Polyphote. An arc lamp adapted to be used, a number in series, upon the same circuit. The electric regulating mechanism is placed in shunt or in parallel with the carbons and arc. (See Lamp, Arc.)

Lamps, Bank of. A number of lamps mounted on a board or other base, and connected to serve as voltage indicator or to show the existence of grounds, or for other purposes.

Lamp, Semi-incandescent. A lamp partaking of the characteristics of both arc and incandescence; a lamp in which the imperfect contact of two carbon electrodes produces a part of or all of the resistance to the current which causes incandescence.

The usual type of these lamps includes a thin carbon rod which rests against a block of carbon. The species of arc formed at the junction of the two heats the carbons. Sometimes the upper carbon or at least its end is heated also by true incandescence, the current being conveyed near to its end before entering it.

Semi-incandescent lamps are not used to any extent now.

Lamp Socket. A receptacle for an incandescent lamp; the lamp being inserted the necessary connections with the two leads are automatically made in most sockets. The lamps may be screwed or simply thrust into the socket and different ones are constructed for different types of lamps. A key for turning the current on and off is often a part of the socket.

Latent Electricity. The bound charge of static electricity. (See Charge, Bound.)

Law of Intermediate Metals. A law of thermo-electricity. The electro-motive force between any two metals is equal to the sum of electro-motive forces between each of the two metals and any intermediate metal in the thermo-electric series, or the electro-motive force between any two metals is equal to the sum of the electromotive forces between all the intermediate ones and the original two metals; it is the analogue of Volta's Law, q. v.

Law of Inverse Squares. When force is exercised through space from a point, its intensity varies inversely with the square of the distance. Thus the intensity of light radiated by a luminous point at twice a given distance therefrom is of one-fourth the intensity it had at the distance in question. Gravitation, electric and magnetic attraction and repulsion and other radiant forces are subject to the same law.

324 STANDARD ELECTRICAL DICTIONARY.

Law of Successive Temperatures. A law of thermo-electricity. The electro-motive force due to a given difference of temperature between the opposite junctions of the metals is equal to the sum of the electro-motive forces produced by fractional differences of temperature, whose sum is equal to the given difference and whose sum exactly fills the given range of temperature.

Law, Right-handed Screw. This rather crude name is given by Emtage to a law expressing the relation of direction of current in a circuit to the positive direction of the axis of a magnet acted on by such current. It is thus expressed: A right-handed screw placed along the axis of the magnet and turned in the direction of the current will move in the positive direction, i. e., towards the north pole of the axis of the magnet.

Lead. A metal; one of the elements; symbol Pb. Atomic weight, 207; equivalent, 103-1/2; valency, 2. Lead may also be a tetrad, when its equivalent is 51.75. The following data are at 0º C. (32º F.) with compressed metal: Relative Resistance, (Silver = l) 13.05 Specific Resistance, 19.63 microhms. Resistance of a wire, (a) 1 ft. long, weighing 1 grain, 3.200 ohms. (b) 1 meter long, weighing 1 gram, 2.232 " (c) 1 meter long, 1 millimeter thick, .2498 " Resistance of 1 inch cube, 7.728 microhms. Electro-Chemical Equivalent (Hydrogen = .0105) 1.086 mgs.

Leading Horns. The tips of pole pieces in a dynamo, which extend in the direction of movement of the armature.

Leading-in Wires. The platinum wires passing through the glass of an incandescent lamp-chamber, to effect the connection of the carbon filament with the wires of the circuit.

Lead of Brushes, Negative. In a motor the brushes are set backwards from their normal position, or in a position towards the direction of armature rotation or given a negative lead instead of a positive one, such as is given to dynamo brushes.

Leak. A loss or escape of electricity by accidental connection either with the ground or with some conductor. There are various kinds of leak to which descriptive terms are applied.

Leakage. The loss of current from conductors; due to grounding at least at two places, or to very slight grounding at a great many places, or all along a line owing to poor insulation. In aerial or pole telegraph lines in wet weather there is often a very large leakage down the wet poles from the wire. (See Surface Leakage--Magnetic Leakage.)

325 STANDARD ELECTRICAL DICTIONARY.

Leakage Conductor. A conductor placed on telegraph poles to conduct directly to earth any leakage from a wire and thus prevent any but a very small portion finding its way into the other wires on the same pole. It presents a choice of evils, as it increases the electrostatic capacity of the line, and thus does harm as well as good. It consists simply of a wire grounded and secured to the pole.

Leg of Circuit. One lead or side of a complete metallic circuit.

Lenz's Law. A law expressing the relations of direction of an inducing current or field of force to the current induced by any disturbance in the relations between such field and any closed conductor within its influence. It may be variously expressed.

(a) If the relative position of two conductors, A and B, be changed, of which A is traversed by a current, a current is induced in B in such a direction that, by its electro-dynamic action on the current in A, it would have imparted to the conductors a motion of the contrary kind to that by which the inducing action was produced. (Ganot.)

(b) The new (induced) current will increase the already existing resistances, or develop new resistance to that disturbance of the field which is the cause of induction. (Daniell.)

(c) When a conductor is moving in a magnetic field a current is induced in the conductor in such a direction as by its mechanical action to oppose the motion. (Emtage.)

(d) The induced currents are such as to develop resistance to the change brought about.

Letter Boxes, Electric. Letter boxes with electrical connections to a bell or indicator of some sort, which is caused to act by putting a letter into the box.

Leyden Jar. A form of static condenser.

In its usual form it consists of a glass jar. Tinfoil is pasted around the lower portions of its exterior and interior surfaces, covering from one-quarter to three-quarters of the walls in ordinary examples. The rest of the glass is preferably shellacked or painted over with insulating varnish, q. v. The mouth is closed with a wooden or cork stopper and through its centre a brass rod passes which by a short chain or wire is in connection with the interior coating of the jar. The top of the rod carries a brass knob or ball.

If such a jar is held by the tinfoil-covered surface in one hand and its knob is held against the excited prime conductor of a static machine its interior becomes charged; an equivalent quantity of the same electricity is repelled through the person of the experimenter to the earth and when removed from the conductor it will be found to hold a bound charge. If the outer coating and knob are both touched or nearly touched by a conductor a disruptive discharge through it takes place.

326 STANDARD ELECTRICAL DICTIONARY.

Fig. 213. LEYDEN JAR WITH DISCHARGER.

If one or more persons act as discharging conductors they will receive a shock. This is done by their joining hands, a person at one end touching the outer coating and another person at the other end touching the knob.

From an influence machine a charge can be taken by connecting the coating to one electrode and the knob to the other.

Fig. 214. SULPHURIC ACID LEYDEN JAR.

327 STANDARD ELECTRICAL DICTIONARY.

Leyden Jar, Sir William Thomson's. An especially efficient form of Leyden jar. It consists of a jar with outer tinfoil coating only. For the interior coating is substituted a quantity of concentrated sulphuric acid. The central rod is of lead with a foot, which is immersed in the acid and from which the rod rises. A wooden cover partly closes the jar, as the central tube through which the rod passes is so large as not to allow the wood to touch it. Thus any leakage from inner to outer coating has to pass over the inside and outside glass surfaces. In the common form of jar the wooden cover may short circuit the uncoated portion of the inner glass surface. In the cut a simplified form of Thomson's Leyden jar is shown, adapted for scientific work.

Lichtenberg's Figures. If the knob of a Leyden jar or other exited electrode is rubbed over the surface of ebonite, shellac, resin or other non-conducting surface it leaves it electrified in the path of the knob. If fine powder such as flowers of sulphur or lycopodium is dusted over the surface and the excess is blown away, the powder will adhere where the surface was electrified, forming what are called Lichtenberg's Figures, Lycopodium and sulphur show both positive and negative figures, that is to say, figures produced by a positively or negatively charged conductor. Red lead adheres only to negative figures. If both positive and negative figures are made and the surface is sprinkled with both red lead and flowers of sulphur each picks out its own figure, the sulphur going principally to the positive one.

The red lead takes the form of small circular heaps, the sulphur arranges itself in tufts with numerous diverging branches. This indicates the difference in the two electricities. The figures have been described as "a very sensitive electrosope for investigating the distribution of electricity on an insulating surface." (Ganot.)

Life of Incandescent Lamps. The period of time a lamp remains in action before the carbon filament is destroyed. The cause of a lamp failing may be the volatilization of the carbon of the filament, causing it to become thin and to break; or the chamber may leak. The life of the lamp varies; 600 hours is a fair estimate. Sometimes they last several times this period.

The higher the intensity at which they are used the shorter is their life. From their prime cost and the cost of current the most economical way to run them can be approximately calculated.

[Transcriber's note: Contemporary incandecent buls are rated for 1000 hours; flourescent bulbs up to 24000 hours; LED lamps up to 100000 hours.]

Lightning. The electrostatic discharge to the earth or among themselves of clouds floating in the atmosphere. The discharge is accompanied by a spark or other luminous effect, which may be very bright and the effects, thermal and mechanical, are often of enormous intensity.

The lightning flash is white near the earth, but in the upper regions where the air is rarefied it is of a blue tint, like the spark of the electric machine. The flashes are often over a mile in length, and sometimes are four or five miles long. They have sometimes a curious sinuous and often a branching shape, which has been determined by photography only recently. To the eye the shape seems zigzag.

328 STANDARD ELECTRICAL DICTIONARY.

In the case of a mile-long flash it has been estimated that 3,516,480 De la Rue cells, q. v., would be required for the development of the potential, giving the flash over three and one-half millions of volts. But as it is uncertain how far the discharge is helped on its course by the rain drops this estimate may be too high.

There are two general types of flash. The so-called zigzag flash resembles the spark of an electric machine, and is undoubtedly due to the disruptive discharge from cloud to earth. Sheet lightning has no shape, simply is a sudden glow, and from examination of the spectrum appears to be brush discharges (see Discharge, Brush) between clouds. Heat lightning is attributed to flashes below the horizon whose light only is seen by us. Globe or ball lightning takes the form of globes of fire, sometimes visible for ten seconds, descending from the clouds. On reaching the earth they sometimes rebound, and sometimes explode with a loud detonation. No adequate explanation has been found for them.

The flash does not exceed one-millionth of a second in duration; its absolute light is believed to be comparable to that of the sun, but its brief duration makes its total light far less than that of the sun for any period of time.

If the disruptive discharge passes through a living animal it is often fatal. As it reaches the earth it often has power enough to fuse sand, producing fulgurites, q. v. (See also Back Shock or Stroke of Lightning.)

Volcanic lightning, which accompanies the eruptions of volcanoes, is attributed to friction of the volcanic dust and to vapor condensation.

[Transcriber's note: The origin of lightning is still (2008) not fully understood, but is thought to relate to charge separation in the vertical motion of water droplets and ice crystals in cloud updrafts. A lightning bolt carries a current of 40,000 to 120,000 amperes, and transfers a charge of about five coulombs. Nearby air is heated to about 10,000 °C (18,000 °F), almost twice the temperature of the Sun’s surface.]

Lightning Arrester. An apparatus for use with electric lines to carry off to earth any lightning discharge such lines may pick up. Such discharge would imperil life as well as property in telegraph offices and the like.

Arresters are generally constructed on the following lines. The line wires have connected to them a plate with teeth; a second similar plate is placed near this with its teeth opposite to those of the first plate and nearly touching it. The second plate is connected by a low resistance conductor to ground. Any lightning discharge is apt to jump across the interval, of a small fraction of an inch, between the oppositely placed points and go to earth.

Another type consists of two plates, placed face to face, and pressing between them a piece of paper or mica. The lightning is supposed to perforate this and go to earth. One plate is connected to the line, the other one is grounded.

The lightning arrester is placed near the end of the line before it reaches any instrument. (See Alternative Paths.)

329 STANDARD ELECTRICAL DICTIONARY.

Fig. 215. COMB OR TOOTHED LIGHTNING ARRESTER.

Fig. 216. FILM OR PLATE LIGHTNING ARRESTER.

Lightning Arrester, Counter-electro-motive Force. An invention of Prof. Elihu Thompson. A lightning arrester in which the lightning discharge sets up a counter-electro-motive force opposed to its own. This it does by an induction coil. If a discharge to earth takes place it selects the primary of the coil as it has low self-induction. In its discharge it induces in the secondary a reverse electro-motive force which protects the line.

Lightning Arrester Plates. The toothed plates nearly in contact, tooth for tooth, or the flat plates of a film lightning arrester, which constitute a lightning arrester. Some advocate restricting the term to the plate connected to the line.

Lightning Arrester, Vacuum. A glass tube, almost completely exhausted, into which the line wire is fused, while a wire leading to an earth connection has its end fused in also.

A high tension discharge, such as that of lightning, goes to earth across the partial vacuum in preference to going through the line, which by its capacity and self-induction opposes the passage through it of a lightning discharge.

It is especially adapted for underground and submarine lines.

330 STANDARD ELECTRICAL DICTIONARY.

Lightning, Ascending. Lightning is sometimes observed which seems to ascend. It is thought that this may be due to positive electrification of the earth and negative electrification of the clouds.

Lightning, Globe or Globular. A very unusual form of lightning discharge, in which the flashes appear as globes or balls of light. They are sometimes visible for ten seconds, moving so slowly that the eye can follow them. They often rebound on striking the ground, and sometimes explode with a noise like a cannon. They have never been satisfactorily explained. Sometimes the phenomenon is probably subjective and due to persistence of vision.

Lightning Jar. A Leyden jar whose coatings are of metallic filings dusted on to the surface while shellacked, and before the varnish has had time to dry. In its discharge a scintillation of sparks appears all over the surface.

Line of Contact. The line joining the points of contact of the commutator brushes in a dynamo or motor.

Synonym--Diameter of Commutation.

Lines of Force. Imaginary lines denoting the direction of repulsion or attraction in a field of force, q. v. They may also be so distributed as to indicate the relative intensity of all different parts of the field. They are normal to equipotential surfaces. (See Electro-magnetic Lines of Force--Electrostatic Lines of Force--Magnetic Lines of Force.)

Lines of Induction. Imaginary lines within a body marking the direction taken within it by magnetic induction. These are not necessarily parallel to lines of force, but may, in bodies of uniform agglomeration, or in crystalline bodies, take various directions.

Synonym--Lines of Magnetic Induction.

Lines of Slope. Lines in a field of force which mark the directions in which the intensity of force in the field most rapidly falls away.

Links, Fuse. Links made of more or less easily fusible metal, for use as safety fuses.

Listening Cam. In a telephone exchange a cam or species of switch used to connect the operator's telephone with a subscriber's line.

331 STANDARD ELECTRICAL DICTIONARY.

Lithanode. A block of compressed lead binoxide, with platinum connecting foils for use as an electrode in a storage battery. It has considerable capacity, over 5 ampere-hours per pound of plates, but has not met with any extended adoption.

Load. In a dynamo the amperes of current delivered by it under any given conditions.

Local Action. (a) In its most usual sense the electric currents within a battery, due to impurities in the zinc, which currents may circulate in exceedingly minute circuits, and which waste zinc and chemicals and contribute nothing to the regular current of the battery. Amalgamated or chemically pure zinc develops no local action.

(b) The term is sometimes applied to currents set up within the armature core or pole pieces of a dynamo. (See Currents, Foucault.)

Local Battery. A battery supplying a local circuit (q. v.); in telegraphy, where it is principally used, the battery is thrown in and out of action by a relay, and its current does the work of actuating the sounder and any other local or station instruments. (See Relay.)

Local Circuit. A short circuit on which are placed local apparatus or instruments. Such circuit is of low resistance and its current is supplied by a local battery, q. v. Its action is determined by the current from the main line throwing its battery in and out of circuit by a relay, q. v., or some equivalent.

Local Currents. Currents within the metal parts of a dynamo. (See Currents, Foucault.) In a galvanic battery. where there is local action, q. v., there are also local currents, though they are not often referred to.

Localization. Determining the position of anything, such as a break in a cable, or a grounding in a telegraph line. In ocean cables two typical cases are the localization of a break in the conductor and of a defect in the insulation admitting water. The first is done by determining the static capacity of the portion of the line which includes the unbroken portion of the conductor; the other by determining the resistance of the line on a grounded circuit.

Locus. A place. The word is used to designate the locality or position of, or series of positions of definite conditions and the like. Thus an isogonic line is the locus of equal declinations of the magnetic needle; it is a line passing through all places on the earth's surface where the condition of a given declination is found to exist.

332 STANDARD ELECTRICAL DICTIONARY.

Lodestone. Magnetic magnetite; magnetite is an ore of iron, Fe3 04 which is attracted by the magnet. Some samples possess polarity and attract iron. The latter are lodestones.

Synonym--Hercules Stone

Logarithm. The exponent of the power to which it is necessary to raise a fixed number to produce a given number. The fixed number is the base of the system. There are two systems; one, called the ordinary system, has 10 for its base, the other, called the Naperian system, has 2.71828 for its base. The latter are also termed hyperbolic logarithms, and are only used in special calculations.

Log, Electric. An apparatus for measuring the speed of a ship. A rotating helical vane of known pitch is dragged behind the vessel. As the helix rotates its movements may actuate electric machinery for registering its rotations. The number of these in a given time, multiplied by the pitch of the vane, gives the distance traversed in such time.

Loop. A portion of a circuit introduced in series into another circuit. The latter circuit is opened by a spring-jack, q. v. or other device, and the loop inserted. By loops any number of connections can be inserted into a circuit in series therewith, and in series or in parallel with one another.

Loop Break. A double bracket or similar arrangement for holding on insulators the ends of a conductor which is cut between them, and to which are connected the ends of a loop. The space between the insulators may be about a foot.

Luces. This may be used as the plural of lux, q. v. It is the Latin plural.

Luminous Jar. A Leyden jar whose coatings are of lozenge-shaped pieces of tinfoil between which are very short intervals. When discharged, sparks appear all over the surface where the lozenges nearly join.

Lux. A standard of illumination, q. v., as distinguished from illuminating power.

It is the light given by one candle at a distance of 12.7 inches--by a carcel, q. v., at a distance of one meter---or by 10,000 candles at 105.8 feet.

It was proposed by W. H. Preece. All the above valuations are identical.

M. (a) Symbol of gaseous pressure equal to one-millionth of an atmosphere.

(b) The Greek m, µ, is used as the symbol of magnetic permeability.

333 STANDARD ELECTRICAL DICTIONARY.

Machine, Cylinder Electric. A frictional electric machine whose rotating glass is in the shape of a cylinder instead of a disc as in the more recent machines.

Fig. 217. PLATE FRICTIONAL ELECTRIC MACHINE.

Machine, Frictional Electric. An apparatus for development of high tension electricity by contact action, brought about by friction.

It consists of a plate or cylinder of glass mounted on insulating standards and provided with a handle for turning it. One or more cushions of leather are held on an insulated support, so as to rub against the plate or cylinder as it is turned. A metal comb or combs are held on another insulating support so as to be nearly in contact with the surface of the glass plate at a point as far removed as possible from the rubbers. The combs are attached to a brass ball or round-ended cylinder, which is termed the prime conductor.

In use either the prime conductor or cushions are connected by a chain or otherwise with the earth. Assume it to be the cushions. As the machine is worked by turning the plate, the glass and cushion being in contact develop opposite electricities. The glass is charged with positive electricity, and as it turns carries it off and as it reaches the prime conductor by induction and conduction robs it of its negative electricity. Meanwhile the cushions negatively excited deliver their charge to the earth. The action thus goes on, the prime conductor being charged with positive electricity.

334 STANDARD ELECTRICAL DICTIONARY.

If the prime conductor is connected to the earth and the cushions are left insulated, negative electricity can be collected from the cushions.

In some machines both prime conductor and cushions are kept insulated and without ground contact. Electrodes connecting with each are brought with their ends close enough to maintain a sparking discharge.

Machine Influence. A static electric machine working by induction to build up charges of opposite nature on two separate prime conductors. In general they are based on the principle of the electrophorous. Work is done by the operator turning the handle. This rotates a disc and draws excited parts of it away from their bound charges. This represents a resistance to mechanical motion. The work absorbed in overcoming this mechanical resistance appears as electric energy. There are various types of influence machines, the Holtz, Toeppler-Holtz and Wimshurst being the most used. The electrophorous, q. v., is a type of influence machine.

Machine, Holtz Influence. A static electric machine. It includes two plates, one of which is rapidly rotated in front of the other. Two armatures of paper are secured to the back of the stationary plate at opposite ends of a diameter. To start it one of these is charged with electricity. This charge by induction acts through the two thicknesses of glass upon a metal bar carrying combs, which lies in front of the further side of the movable plate. The points opposite the armature repel electrified air, which strikes the movable disc and charges it. A second rod with comb at the opposite end of the same diameter acts in the reverse way. Thus opposite sections of the disc are oppositely charged and the combs with them. By induction these portions of the disc react upon the two armatures. The opposite electricities escape from the armatures by paper tongues which are attached thereto and press against the back of the movable plate. As the plate rotates the opposite electricities on its face neutralize the electricity repelled from the combs. The charges on the back strengthen the charges of the armatures and brass combs. Thus the machine builds up, and eventually a discharge of sparks takes place from the poles of the brass combs.

335 STANDARD ELECTRICAL DICTIONARY.

Machine, Toeppler-Holtz. A modification of the Holtz machine. The priming charge of the armatures is produced by friction of metallic brushes against metallic buttons on the face of the rotating plate. (See Machine, Holtz.)

Machine, Wimshurst. A form of static influence machine. It consists of two plates of glass, on which radial sectors of tinfoil are pasted. Both plates are rotated in opposite directions. The sectors of the two plates react one upon the other, and electric charges of opposite sign accumulate on the opposite sides of the plates and are collected therefrom by collecting combs.

Mack. A name, derived from Maxwell, and suggested for the unit of inductance. It is due to Oliver Heaviside, but has never been adopted. (See Henry.)

Magne-Crystallic Action. The action of a supposed force of the same name, proposed by Faraday. It relates to the different action of a magnetic field upon crystalline bodies, according to the position of their axes of crystallization. A needle of tourmaline, normally paramagnetic, if poised with its axis horizontal, is diamagnetic. Bismuth illustrates the same phenomenon. The subject is obscure. Faraday thought that he saw in it the action of a specific force.

Magnet. A body which tends when suspended by its centre of gravity to lay itself in a definite direction, and to place a definite line within it, its magnetic axis, q. v., in a definite direction, which, roughly speaking, lies north and south. The same bodies have the power of attracting iron (Daniell), also nickel and cobalt.

Magnets are substances which possess the power of attracting iron. (Ganot.)

[Transcriber's note: Edward Purcell and others have explained magnetic and electromagnetic phenomenon as relativistic effects related to electrostatic attraction. Magnetism is caused by Lorentz contraction of space along the direction of a current. Electromagnetic waves are caused by charge acceleration and the resulting disturbance of the electrostatic field. (Electricity and Magnetism: Berkeley Physics Course Volume 2, 1960)]

Magnet, Anomalous. A magnet possessing more than the normal number (two) of poles. If two straight magnets are placed end to end with their south poles in juxtaposition the compound bar will seem to possess three poles, one at each end and one in the middle. The apparent pole in the middle is really made up of two consequent poles, q. v. It sometimes happens that when a single long thin bar is magnetized consequent poles are produced, although such magnet is in one piece. This may be accidental, as in such case it is quite hard to avoid anomalous poles, or, as in the field magnets of some forms of dynamos, anomalous poles may be purposely produced.

Magnet, Artificial. A magnet formed artificially by any method of magnetization (see Magnetism) applicable to permanent magnets, electro-magnets and solenoids. It expresses the distinction from the natural magnets or lodestone, q. v. It is made of steel in practice magnetized by some of the methods described under Magnetization.

336 STANDARD ELECTRICAL DICTIONARY.

Magnet, Axial. A straight-solenoid with axial core.

Magnet, Bar. A bar magnet is one in the shape of a bar, i. c., straight with parallel sides and considerably longer than wide or deep.

Magnet, Bell-shaped. A form of permanent magnet used in some galvanometers. In shape it is a thick-sided cylindrical box with two slots cut out of opposite sides, so as to make it represent a horseshoe magnet. Its shape enables it to be surrounded closely by a mass of copper, for damping its motion, to render the instrument dead-beat. Such a magnet is used in Siemens & Halske's galvanometer.

Magnet Coil. A coil to be thrust over an iron core, to make an electro-magnet. They are often wound upon paper or wooden bobbins or spools, so as to be removable from the core if desired.

Magnet, Compensating. (a) A magnet fastened near a compass on an iron or steel ship to compensate the action of the metal of the ship upon the magnetic needle. The ship itself always has some polarity and this is neutralized by one or more compensating magnets.

(b) See below.

Magnet, Controlling. A magnet attached to a galvanometer by which the directive tendency of its magnetic needle is adjusted. In the reflecting galvanometer it often is a slightly curved magnet carried by a vertical brass spindle rising from the center of the instrument, and which magnet may be slid up and down on the spindle to regulate or adjust its action.

Synonym--Compensating Magnet.

Magnet, Compound. A permanent magnet, built up of a number of magnets. Small bars can be more strongly magnetized than large. Hence a compound magnet may be made more powerful than a simple one.

Magnet Core. The iron bar or other mass of iron around which insulated wire is wound for the production of an electro-magnet. The shapes vary greatly, especially for field magnets of dynamos and motors. For these they are usually made of cast iron, although wrought iron is preferable from the point of view of permeability.

Magnet, Damping. A damping magnet is one used for bringing an oscillating body to rest. The body may be a metallic disc or needle, and the action of the magnet depends on its lines of force which it establishes, so that the body has to cut them, and hence has its motion resisted.

337 STANDARD ELECTRICAL DICTIONARY.

Magnet, Deflection of. The change of position of a magnet from the plane of the earth's meridian in which it normally is at rest into another position at some angle thereto, by the effect of an artificial magnetic field, as the deflection of a galvanometer needle.

Magnet, Electro-. A magnet consisting of a bar of iron, bundle of iron wires, iron tube or some equivalent, around which a coil of insulated wire is wound. Such combination becomes polarized when a current is passed through it and is an active magnet. On the cessation of the current its magnetism in part or almost completely disappears. (See Electro-magnet.)

Magnet, Equator of. In a magnet the locus of points of no attractive power and of no polarity. In a symmetrical, evenly polarized magnet it is the imaginary line girdling the centre. The terms Neutral Point or Neutral Line have displaced it.

Synonyms--Neutral Line--Neutral Point.

Magnet, Field. A magnet, generally an electro-magnet, used to produce the field in a dynamo or motor.

Magnet, Haarlem. Celebrated magnets made in Haarlem, Holland. Logeman, Van Wetteren, Funckler and Van der Willigen were the makers who gave the celebrity to the magnets. They were generally horseshoe magnets, and would carry about twenty times their own weight.

Magnet, Horseshoe. A magnet of U shape--properly one with the poles brought a little closer together than the rest of the limbs. For direct lifting and attractive effects it is the most generally adopted type. Its advantage as regards lifting effect is due to small reluctance, q. v., offered by a complete iron circuit, such as the armature and magnet together produce. As the term is now used it is applied to any U shaped magnet.

Fig. 218. JOULE'S ELECTRO-MAGNET.

Magnet, Joule's Electro. An electro-magnet of the shape of a cylinder with a longitudinal segment cut-off. It is wound with wire as shown. The segment cut-off is a piece of the same shape as the armature. It is of high power.

338 STANDARD ELECTRICAL DICTIONARY.

Magnetic Adherence. The tendency of a mass of iron to adhere to the poles of a magnet. It is best figured as due to the virtual shortening of lines of force, as the more permeable iron gives a better path for them than the air can afford, and consequently a virtually shorter one.

Magnetic Attraction and Repulsion. The attraction of a magnet for iron, steel, nickel and cobalt and of unlike poles of magnets for each other. It is identical with electro-magnetic attraction, q.v. (Also see Electro-magnetism.)

Magnetic Attraction and Repulsion, Coulomb's Law of. Magnetic attraction and repulsion are inversely as the square of the distance. (Ganot.)

While theoretically true in the case of isolated poles, in practise it does not generally apply on account of the large diameter and relative shortness of magnets.

Magnetic Axis. The line connecting the poles of a magnet. It does not generally coincide exactly with any symmetrical axis of figure. In such cases an error is introduced into the indications of the needle which must be determined and allowed for in compasses. To determine it with a magnetic needle the suspension cup is made removable, so that the needle can be reversed. Readings are taken with one side of the needle and then with the other side of the needle up, and the average corresponds with the position of the magnetic axis in both positions of the needle.

Magnetic Azimuth. The angle, measured on a horizontal circle, between the magnetic meridian and a great circle of the earth passing through the observer and any observed body. It is the astronomical azimuth of a body referred to the magnetic meridian and therefore subject to the variation of the compass. The angle is the magnetic azimuth of the observed body.

Magnetic Battery. A name for a compound permanent magnet; one made up by bolting or clamping together, or to single soft iron pole pieces, a number of single permanent magnets. There are a number of forms of compound magnets. In making them care has to be taken to have them of even strength. It is also well to have them slightly separated. The object of both these precautions is to prevent a stronger element or magnet from depolarizing its neighbor.

Synonym--Compound Magnet.

Magnetic Bridge. An apparatus for testing the relative permeability of iron. It consists of a rectangular system of iron cores. Three of the sides are wound with wire as shown. The other side is built up of double bars, and from the centre two curved arms rise, as shown in the cut. The arms do not touch. Between them a short magnet is suspended by a filament, which also carries a mirror and an index.

339 STANDARD ELECTRICAL DICTIONARY.

Fig. 219. MAGNETIC BRIDGE.

A lamp and scale are provided as in the reflecting galvanometer. When adjusted the magnetic needle hangs as shown in the cut, Fig. 219, without any tendency to turn towards either curved pole piece. If all iron parts are symmetrical and of similar metal, a current through the coils will make no difference. It will work in magnetic opposition upon the two arms, or, in other words, will maintain both arms at identical potential.

Fig. 220. POLE PIECES, MAGNETIC NEEDLE AND MIRROR OF MAGNETIC BRIDGE.

If there is the least difference in permeability, length or thickness between any of the iron bars the magnetic potential of the two curved arms will differ, and the magnetic needle will turn one way or the other. In practical use different samples of iron are substituted for the unwound members of the fourth side of the parallelogram, and the needle by its motions indicates the permeability.

In the cut, Fig. 220, D D are the ends of the curved pole pieces; A the wire carrying the mirror B and magnetic needle N, and E is the index which shows the larger deflections.

340 STANDARD ELECTRICAL DICTIONARY.

Magnetic Circuit. A magnetic field of force is characterized by the presence of lines of force, which, while approximately parallel, curve around and tend to form closed curves. The polarity of a field of force is referred to an imaginary direction of the lines of force from the north pole through space to the south pole, and in the part of the field corresponding to the body of the magnet, from the south to the north pole. The cut indicates these features. Hence the magnetic field of force is termed the magnetic circuit, and to it are attributed a species of resistance termed reluctance, q. v., and the producing cause of the field or lines of force is termed sometimes magneto-motive force, q. v.) corresponding to the electro-motive force. The modern treatment of the magnetic circuit is similar to the application of Ohm's law and the laws of resistance and conductivity to the electric circuit.

Magnetic Circuit, Double. A magnetic circuit which virtually represents two horseshoe magnets placed with their like poles in contact. It is used for field magnets, the armatures occupying a place between the consequent poles.

Fig. 221. ONE-HALF PORTION OF A DOUBLE MAGNETIC CIRCUIT.

Magnetic Concentration of Ores. The concentration of ores or the freeing them from their gangue by magnetic attraction. It is only applicable to those cases in which either the ore itself or the gangue is attracted by the magnet. Its principal application is to the concentration of magnetic iron sands. (See Magnetic Concentration.)

Magnetic Concentrator. An apparatus similar to a magnetic separator, q. v., but used to concentrate magnetic iron sands. By the action of electro-magnets the magnetic iron sand (magnetite) is separated from the sand with which it is mixed.

Magnetic Conductivity and Conductance. The first notion of permeance and of the magnetic circuit included the idea of magnetic conductivity, which conducted lines of force urged by magneto-motive force through a magnetic circuit. The terms are displaced by permeability and permeance.

341 STANDARD ELECTRICAL DICTIONARY.

Magnetic Continuity. The completeness of a magnetic circuit, as when the armature of a horseshoe magnet is in contact with both poles. It is an attribute of a paramagnetic substance only and is identical for permanent magnets or for electro-magnets. An air space intervening between armature and magnet poles, or a space filled with any diamagnetic substance prevents continuity, although the lines of force to some extent still find their way around. The leakage is increased by discontinuity.

Magnetic Control. Control of a magnetic needle, magnet, iron index or armature, in a galvanometer, ammeter or voltmeter by a magnetic field; the restitutive force being derived from a permanent magnet.

Magnetic Couple. The couple of magnetic force which tends to bring the magnetic needle into the plane of the magnetic meridian. One force is represented by the imaginary pull upon the north pole, and the other by the opposite pull upon the south pole of the needle. The moment of the couple varies from a maximum when the needle is at right angles to the plane of the magnetic meridian to zero when it is in such plane.

Magnetic Creeping. Viscous hysteresis; the slow increase of magnetism in a paramagnetic body when exposed to induction.

Fig. 222. MAGNETIC CURVES OR FIGURES.

Magnetic Curves. The pictorial representation of magnetic lines of force. It is generally produced by scattering filings on a sheet of paper or pane of glass held over a magnet. The filings arrange themselves in characteristic curves. Tapping the paper or pane of glass facilitates the arrangement, or jarring the filings off a smaller magnet, so that they fall polarized upon the paper, is thought by some to improve the effect. The group of curves forms what are termed magnetic figures, q. v.

342 STANDARD ELECTRICAL DICTIONARY.

Magnetic Declination. The angular deviation of the magnetic needle, causing it to rest at an angle with the true meridian; the variation of the compass. (See Magnetic Elements.)

Magnetic Density. The intensity of magnetization expressed in lines of force per stated area of cross-section in a plane at right angles to the lines of force.

Magnetic Dip. The inclination from the horizontal assumed by a magnetic needle free to move in the vertical plane. (See Magnetic Elements.) The angle of dip or inclination is entirely a function of the earth, not of the needle.

Magnetic Discontinuity. A break or gap in a magnetic circuit. To make a complete circuit the iron or other core must be continuous. If the armature of a horseshoe magnet is in contact with both poles the continuity is complete. If the armature is not in contact magnetic continuity gives place to discontinuity. It is an attribute of a paramagnetic substance only, and is identical for permanent magnets, or for electro-magnets.

Magnetic Elements. The qualities of the terrestrial magnetism at any place as expressed in its action upon the magnetic needle. Three data are involved.

I. The Declination or Variation. II. The Inclination or Dip. III. The Force or Intensity.

I. The Declination is the variation expressed in angular degrees of the magnetic needle from the true north and south, or is the angle which the plane of the magnetic meridian makes with that of the geographical meridian. It is expressed as east or west variation according to the position of the north pole; east when the north pole of the needle is to the east of the true meridian, and vice versa. Declination is different for different places; it is at present west in Europe and Africa, and east in Asia and the greater part of North and South America. The declination is subject to (a) secular, (b) annual and (c) diurnal variations. These are classed as regular; others due to magnetic storms are transitory and are classed as irregular, (a) Secular variations. The following table shows the secular variations during some three hundred years at Paris. These changes are termed secular, because they require centuries for their completion.

343 STANDARD ELECTRICAL DICTIONARY.

Table of Declination or Variation at Paris. Year. Declination. 1580 11º 30' E. 1663 0° 1700 8° 10' W. 1780 19º 55' W. 1785 22º 00' W. 1805 22º 5' W. 1814 22º 34' W. 1825 22° 22' W. 1830 22º 12' W. 1835 22º 4' W. 1850 20º 30' W. 1855 19º 57' W. 1860 19º 32' W. 1865 18º 44' W. 1875 17º 21' W. 1878 17º 00' W. [Transcriber's note The value for 2008 is about 0° 48' W, changing by 0° 7' E/year.]

On scrutinizing these figures it will be seen that there is part of a cycle represented and that the declination is slowly returning to the zero point after having reached its maximum western variation in 1814. Upwards of 300 years would be required for its completion on the basis of what is known. In other places, notably the coast of Newfoundland, the Gulf of the St. Lawrence and the rest of the North American seaboard and in the British Channel, the secular variations are much more rapid in progress. (b) Annual variations--These were first discovered in 1780 by Cassini. They represent a cycle of annual change of small extent, from 15' to 18' only. In Paris and London the annual variation is greatest about the vernal equinox, or March 21st, and diminishes for the next three months, and slowly increases again during the nine following months. It varies during different epochs. (c) Diurnal variations were discovered in 1722 by Graham. A long needle has to be employed, or the reflection of a ray of light, as in the reflecting galvanometer, has to be used to observe them. In England the north pole of the magnetic needle moves every day from east to west from sunrise until 1 or 2 P. M.; it then tends towards the east and recovers its original position by 10 P. M. During the night the needle is almost stationary. As regards range the mean amplitude of diurnal variations at Paris is from April to September 13' to 15'; for the other months from 8' to 10'. On some days it amounts to 25' and sometimes is no more than 5'. The amplitude of diurnal variations decreases from the poles to the equator. Irregular variations accompany earthquakes, the aurora borealis and volcanic eruptions. In Polar regions the auroral variations may be very great; even at 40° latitude they may be 1° or 2°. Simultaneous irregularities sometimes extend over large areas. Such are attributed to magnetic storms. II. The Inclination is the angle which the magnetic needle makes with the horizon, when the vertical plane in which the needle is assumed to be free to move coincides with the magnetic meridian. It is sometimes called the dip of the needle. It varies as does the declination, as shown in the following table of inclinations of London.

344 STANDARD ELECTRICAL DICTIONARY.

Table of Inclination or Dip at London Year. Inclination. 1576 71° 50' 1600 72° 1676 73° 30' 1723 74° 42' 1773 72° 19' 1780 72° 8' 1790 71° 33' 1800 70° 35' 1821 70° 31' 1828 69° 47' 1838 69° 17' 1854 68° 31' 1859 68° 21' 1874 67° 43' 1876 67° 39' 1878 67° 36' 1880 67° 35' 1881 67° 35'

III. Force or Intensity is the directive force of the earth. It varies with the squares of the number of oscillations the magnetic needle will make if caused to oscillate from a determined initial range. The intensity is supposed to be subject to secular change. According to Gauss the total magnetic intensity of the earth is equal to that which would be exerted if in each cubic yard there were eight bar magnets, each weighing one pound. This is, of course, a rough way of expressing the degree of intensity. Intensity is least near the magnetic equator and greatest near the magnetic poles; the places of maximum intensity are termed the magnetic foci. It varies with the time of day and possibly with changes in altitude.

Magnetic Elongation. The elongation a bar of iron or steel undergoes when magnetized. By magnetization it becomes a little longer and thinner, there being no perceptible change in volume. The change is accompanied by a slight sound--the magnetic tick. An exceedingly delicate adjustment of apparatus is required for its observation.

Magnetic Equator. A locus of the earth's surface where the magnet has no tendency to dip. It is, approximately speaking, a line equally distant from the magnetic poles, and is called also the aclinic line. It is not a great circle of the earth.

345 STANDARD ELECTRICAL DICTIONARY.

Magnetic Field of Force. The field of force established by a magnet pole. The attractions and repulsions exercised by such a field follow the course of the electro- magnetic lines of force. (See also Field of Force.) Thus the tendency of a polarized needle attracted or repelled is to follow, always keeping tangential to curved lines, the direction of the lines of force, however sweeping they may be. The direction of magnetic lines of force is assumed to be the direction in which a positive pole is repelled or a negative one attracted; in other words, from the north pole of a magnet to its south pole in the outer circuit. The direction of lines of force at any point, and the intensity or strength of the field at that point, express the conditions there. The intensity may bc expressed in terms of that which a unit pole at unit distance would produce. This intensity as unitary it has been proposed to term a Gauss. (See Weber.)

The direction of the lines of force in a magnetic field are shown by the time-honored experiment of sprinkling filings of iron upon a sheet of paper held over a magnet pole or poles. They arrange themselves, if the paper is tapped, in more or less curved lines tending to reach from one pole of the magnet to the other. Many figures may be produced by different conditions. Two near poles of like name produce lines of force which repel each other. (See Magnetic Curves.)

A magnetic and an electro-magnetic field are identical in all essential respects; the magnetic field may be regarded as a special form of the electro-magnetic field, but only special as regards its production and its defined north and south polar regions.

Synonyms--Magnetic Spin (not much used).

Magnetic Field, Uniform. A field of identical strength in all parts, such as the earth's magnetic field. If artificially produced, which can only be approximately done, it implies large cross-section of magnet pole in proportion to the length of the magnetic needle affected by it, which is used in determining its uniformity.

Magnetic Figures. The figures produced by iron filings upon paper or glass held near magnetic poles. By these figures the direction of lines of force is approximately given, and a species of map of the field is shown. (See Magnetic Field of Force--Magnetic Curves.)

Magnetic Filament. The successive rows of polarized molecules assumed to exist in magnetized iron. Each molecule represents an infinitely small magnet, and its north pole points to the south pole of the next molecule. Such a string or row is a theoretical conception based on the idea that the molecules in a magnet are all swung in to parallelism in the magnetizing process. A magnetic filament may be termed the longitudinal element of a magnet. (See Magnetism, Hughes' Theory of.)

[Transcriber's note: This description parallels the modern notion of electron spin as the basis of magnetism in materials.]

Magnetic Fluids. A two-fluid theory of magnetism has been evolved, analogous to the two-fluid theory of electricity. It assumes north fluid or "red magnetism" and a south fluid or "blue magnetism." Each magnetism is supposed to predominate at its own pole and to attract its opposite. Before magnetization the fluids are supposed to neutralize each other about each molecule; magnetization is assumed to separate them, accumulating quantities of them at the poles.

Magnetic Flux. Magnetic induction; the number of lines of force that pass through a magnetic circuit.

Synonym--Magnetic Flow.

346 STANDARD ELECTRICAL DICTIONARY.

Magnetic Force. The forces of attraction and repulsion exercised by a magnet. By Ampere's theory it is identical with the forces of attraction and repulsion of electric currents.

Magnetic Friction. The damping effect produced on the movements of a mass of metal by proximity to a magnet; the phenomenon illustrated in Arago's wheel, q. v. When a mass of metal moves in the vicinity of a magnet it cuts the lines of force emanating from its poles, thereby producing currents in its mass; as the production of these currents absorbs energy a damping effect is produced upon the movements of the mass.

Magnetic Gear. Friction gear in which electro-magnetic adherence is employed to draw the wheels together. (See Adherence, Electro-magnetic--Electro-magnetic Friction Gear.)

Magnetic Inclination. The inclination from the horizontal of a magnetic needle placed in the magnetic meridian. (See Magnetic Element--Inclination Map.)

Synonym--Magnetic Dip.

Magnetic Induction. The force of magnetization within an induced magnet. It is in part due to the action of the surrounding particles of polarized material; in part to the magnetic field. (See Magnetic Induction, Coefficient of.)

In a more general way it is the action of a magnet upon bodies in its field of force. In some cases the magnetism induced causes the north pole of the induced magnet to place itself as far as possible from the north pole of the inducing magnet and the same for the south poles. Such substances are called paramagnetic or ferromagnetic. They lie parallel or tangential to the lines of force. In other cases the bodies lie at right angles or normal to the lines of force. Such bodies are called diamagnetic.

Some bodies are crystalline or not homogeneous in structure, and in them the lines of magnetic induction may take irregular or eccentric paths. (See AEolotropic.)

Synonym--Magnetic Influence.

Magnetic Induction, Apparent Coefficient of. The apparent permeability of a paramagnetic body as affected by the presence of Foucault currents in the material itself. These currents act exactly as do the currents in the coils surrounding the cores of electro-magnets. They produce lines of force which may exhaust the permeability of the iron, or may, if in an opposite direction, add to its apparent permeability.

Magnetic Induction, Coefficient of. The number, obtained by dividing the magnetization of a body, expressed in lines of force produced in it, by the magnetizing force which has produced such magnetization, expressed in lines of force producible by the force in question in air. It always exceeds unity for iron, nickel and cobalt. It is also obtained by multiplying the coefficient of induced magnetization by 4 PI (4 * 3.14159) and adding 1. (See Magnetic Susceptibility--Magnetization, Coefficient of Induced.)

347 STANDARD ELECTRICAL DICTIONARY.

The coefficient of magnetic induction varies with the material of the induced mass, and varies with the intensity of the magnetizing force. This variation is due to the fact that as the induced magnetism in a body increases, the magnetizing force required to maintain such induction, increases in a more rapid ratio. The coefficient of magnetic induction is the same as magnetic permeability, and in a certain sense is the analogue of conductivity. It is also termed the multiplying power of the body or core magnetized. It is the coefficient of induced magnetization (see Magnetization, Coefficient of Induced) referred to a mass of matter. For diamagnetic bodies the coefficient has a negative sign; for paramagnetic bodies it has a positive sign.

Synonyms--Permeability--Multiplying Power--Magnetic Inductive Capacity.

Magnetic Induction, Dynamic. The induction produced by a magnetic field which moves with respect to a body, or where the body if moving moves at a different rate, or where the body moves and the field is stationary. In the case where both move, part of the induction may be dynamic and part static. (See Magnetic Induction, Static.)

Magnetic Induction, Static. Magnetic induction produced by a stationary field acting upon a stationary body.

Magnetic Induction, Tube of. An approximate cylinder or frustrum of a cone whose sides are formed of lines of magnetic induction. (See Magnetic Induction, Lines of.) The term tube is very curiously applied in this case, because the element or portion of a magnetic field thus designated is in no sense hollow or tubular.

Magnetic Inertia. A sensible time is required to magnetize iron, or for it to part with its magnetism, however soft it may be. This is due to its magnetic inertia and is termed the lag. Permanent or residual magnetism is a phase of it. It is analogous to self-induction of an electric circuit, or to the residual capacity of a dielectric.

Magnetic Insulation. Only approximate insulation of magnetism is possible. There is no perfect insulator. The best ones are only 10,000 times less permeable than iron. Hence lines of force find their way through air and all other substance, being simply crowded together more in paths of iron or other paramagnetic substance.

348 STANDARD ELECTRICAL DICTIONARY.

Magnetic Intensity. The intensity of the magnetization of a body. It is measured by the magnetic lines of force passing through a unit area of the body, such area being at right angles to the direction of the lines of force.

Magnetic Lag. In magnetism the tendency of hard iron or steel especially to take up magnetism slowly, and to part with it slowly. (See Magnetic Inertia.) The lag affects the action of a dynamo, and is a minor cause of those necessitating the lead of the brushes.

Synonym--Magnetic Retardation.

Magnetic Latitude. Latitude referred to the magnetic equator and isoclinic lines.

Magnetic Leakage. The lines of force in a field magnet which pass through the air and not through the armature are useless and represent a waste of field. Such lines constitute magnetic leakage.

Magnetic Limit. The temperature beyond which a paramagnetic metal cannot be magnetized. The magnetic limit of iron is from a red to a white heat; of cobalt, far beyond a white heat; of chromium, below a red heat; of nickel at about 350° C. (662°F.) of manganese, from 15° C. to 20° C. (59° to 68° F.)

Magnetic Lines of Force. Lines of force indicating the distribution of magnetic force, which is due presumably to whirls of the ether. A wire or conductor through which a current is passing is surrounded by an electro-magnetic field of force, q. v., whose lines of force form circles surrounding the conductor in question. A magnet marks the existence of a similar electro-magnetic field of force whose lines form circuits comprising part of and in some places all of the body of the magnet, and which are completed through the air or any surrounding paramagnetic or diamagnetic body. They may be thought of as formed by the Ampérian sheet of current, and analogous to those just mentioned as surrounding a conductor.

Fig. 223. MAGNETIC LINES OF FORCE, DIRECTION OF.

A magnetic line of force may be thought of as a set of vortices or whirls, parallel to each other, and strung along the line of force which is the locus of their centres.

If as many lines are drawn per square centimeter as there are dynes (per unit pole) of force at the point in question, each such line will be a unitary c. g. s. line of force.

349 STANDARD ELECTRICAL DICTIONARY.

Magnetic Mass. A term for a quantity of magnetism. Unit mass is the quantity which at unit distance exercises unit force.

Magnetic Matter. Imaginary matter assumed as a cause of magnetism. Two kinds, one positive and one negative, may be assumed as in the two fluid theory of electricity, or only one kind, as in the single fluid theory of electricity. Various theories of magnetic matter have been presented whose value is only in their convenience.

[Transcriber's note: See "magnet" and Edward Purcell's explanation of magnetism using general relativity.]

Magnetic Memory. The property of retaining magnetism; coercive force; magnetic inertia; residual magnetism.

[Transcriber's note: Small ferrite magnetic donuts were used as computer main memory from 1950 to 1970.]

Magnetic Meridian. A line formed on the earth's surface by the intersection therewith of a plane passing through the magnetic axis. It is a line determined by the direction of the compass needle. The meridians constantly change in direction and correspond in a general way to the geographical meridians.

Magnetic Moment. The statical couple with which a magnet would be acted on by a uniform magnetic field of unit intensity if placed with its magnetic axis at right angles to the lines of force of the field. (Emtage.) A uniformly and longitudinally magnetized bar has a magnetic moment equal to the product of its length by the strength of its positive pole.

Magnetic Needle. A magnet with a cup or small depression at its centre and poised upon a sharp pin so as to be free to rotate or oscillate in a horizontal plane. The cup is often made of agate. Left free to take any position, it places its magnetic axis in the magnetic meridian.

Magnetic Parallels. Lines roughly parallel to the magnetic equator on all parts of each of which the dip of the magnetic needle is the same; also called Isoclinic Lines. These lines mark the places of the intersection of equipotential surfaces with the earth's surface. They are not true circles, and near the poles are irregular ellipses; the magnet there points toward their centres of curvature. They correspond in a general way with the Geographical Parallels of Latitude.

Magnetic Permeability. The specific susceptibility of any substance, existing in a mass, for magnetic induction. (See Magnetic Induction, Coefficient of, synonym for Magnetic Permeability and Magnetization, Coefficient of Induced.)

Synonyms--Magnetic Inductive Capacity--Multiplying Power--Coefficient of Magnetic Induction.

350 STANDARD ELECTRICAL DICTIONARY.

Magnetic Perturbations. Irregular disturbances of the terrestrial magnetism, as by the aurora and in electric storms.

Magnetic Poles. The points where the equipotential surfaces of the terrestrial field of force graze the earth's surface; the points toward which the north or south poles of the magnetic needle is attracted. Over a magnetic pole the magnetic needle tends to stand in a vertical position. There are two poles, Arctic or negative, and Antarctic or positive. Magnetic needles surrounding them do not necessarily point toward them, as they point to the centres of curvature of their respective magnetic parallels. The poles constantly change in position. The line joining them does not coincide with anything which may be termed the magnetic axis of the earth.

Magnetic Poles, False. Poles on the earth's surface other than the two regular magnetic poles. There seem by observation to be several such poles, while analogy would limit true magnetic poles to two in number.

Magnetic Potential. The potential at any point of a magnetic field is the work which would be done by the magnetic forces of the field upon a positive unit of magnetism as it moves from that point to an infinite distance. (Emtage.)

Magnetic Proof Piece. A piece of iron used for testing magnets and the distribution of magnetism in bars, by suspending or supporting above or near the magnet, by detaching after adherence, and in other ways.

Magnetic Proof Plane. An exploring coil used for testing the distribution of magnetism. It is connected in circuit with a galvanometer, and exposed to alternation of current, or to other disturbing action produced by the magnet or field under examination. This affects the galvanometer, and from its movements the current produced in the coil, and thence the magnetic induction to which it was exposed, are calculated.

Synonym--Exploring Coil.

Magnetic Quantity. The magnetism possessed by a body; it is proportional to the action of similar poles upon each other, or to the field produced by the pole in question. It is also called the strength of a pole.

The force exercised by two similar poles upon each other varies with their product and inversely with the square of the distance separating them; or it may be expressed thus (m * m) / (L^2). This is a force, and the dimensions of a force are ML/(T^2). Therefore, (m^2)/(L^2) = ML/(T^2) or m = (M^.5)*(L^1.5)/T.

351 STANDARD ELECTRICAL DICTIONARY.

Magnetic Reluctance. The reciprocal of permeance; magnetic resistance; the relative resistance to the passage of lines of force offered by different substances. The idea is derived from treating the magnetic circuit like an electric one, and basing its action on magneto-motive force acting through a circuit possessing magnetic reluctance.

Magnetic Reluctivity. The reciprocal of magnetic permeability, q. v.

Synonym--Magnetic Resistance.

Magnetic Retentivity. The property of steel or hard iron by which it slowly takes up and slowly parts with a magnetic condition--traditionally (Daniell) called coercitive force.

Magnetic Rotary Polarization. If a plane polarized beam of light is sent through a transparent medium in a magnetic field its plane of polarization is rotated, and this phenomenon is denoted as above. (Compare Refraction, Electric, and see Electro-magnetic Stress.) This has been made the basis of a method for measuring current. A field of force varies with the current; the polarization produced by such field is therefore proportional to the current. (Becquerel & Rayleigh.)

A plane polarized beam of light passing through the transparent medium in the magnetic field by the retardation or acceleration of one of its circular components has its plane of polarization rotated as described. The direction of the lines of force and the nature of the medium determine the sense of the rotation; the amount depends upon the intensity of the field resolved in the direction of the ray, and on the thickness and nature of the medium.

Magnetic Saturation. The maximum magnetic force which can be permanently imparted to a steel bar. A bar may be magnetized beyond this point, but soon sinks to it. The magnetism produced in a bar is prevented from depolarization by the retentivity or coercive force of the bar. The higher the degree of magnetization the greater the tendency to depolarization.

It is also defined as the maximum intensity of magnetism produced in a paramagnetic substance by a magnetic field as far as affected by the permeability of the substance in question. The more lines of force passed through such a substance the lower is its residual permeability. It is assumed that this becomes zero after a certain point, and then the point of saturation is reached. After this point is reached the addition of any lines of force is referred entirely to the field and not at all to the permeability of the substance. But such a zero is only definable approximately.

Magnetic Screen. A box or case of soft iron, as thick as practicable, for protecting bodies within it from the action of a magnetic field. The lines of force to a great extent keep within the metal of the box on account of its permeability, and but a comparatively few of them cross the space within it.

Such screens are used to prevent watches from being magnetized, and are a part of Sir William Thomson's Marine galvanometer.

A magnetic screen may be a sphere, an infinite or very large plane, or of the shape of any equipotential surface.

Synonym--Magnetic Shield.

352 STANDARD ELECTRICAL DICTIONARY.

Magnetic Self-induction. The cause of a magnet weakening is on account of this quality, which is due to the direction of the lines of force within a magnet from the positive towards the negative pole. "A magnet thus tends to repel its own magnetism and to weaken itself by self-induction." (Daniell.)

Magnetic Separator. An apparatus for separating magnetic substances from mixtures. Such separators depend on the action of electro-magnets. In one form the material falls upon an iron drum, magnetized by coils. Any magnetic substance adheres to the drum and is thereby separated. They are used by porcelain makers for withdrawing iron particles from clay, by machinists to separate iron filings and chips from brass, and for similar purposes.

Fig. 224. MAGNETIC SEPARATOR.

Magnetic Shell. A theoretical conception of a cause of a magnetic field or of a distribution of magnetism. If we imagine a quantity of very short magnets arranged in contact with their like poles all pointing in the same direction so as to make a metal sheet, we have a magnetic shell. Its magnetic moment is equal to the sum of the magnetic moment of all its parts. If the shell is of uniform strength the magnetic moment of a unit area gives the strength of the shell; it is equal to the magnetic quantity per unit of area, multiplied by the thickness of the shell.

If its strength is uniform throughout a magnetic shell is called simple; if its strength varies it is termed complex.

Emtage thus defines it: A magnetic shell is an indefinitely thin sheet magnetized everywhere in the direction normal to itself.

Magnetic Shell, Strength of. The magnetic quantity per unit of area of the shell multiplied by the thickness of the shell.

353 STANDARD ELECTRICAL DICTIONARY.

Magnetic Shield. In general a magnetic screen, q. v. Sometimes a strong local field is made to act as a shield, by its predominance overcoming any local or terrestrial field to which the needle to be protected may be exposed.

Magnetic Shunt. The conception of a magnetic circuit being formed, the shunt is a corollary of the theory. It is any piece of iron which connects points of a magnet differing in polarity, so as to divert part of the lines of force from the armature or yoke. The shunt is especially applicable in the case of horseshoe magnets. Thus a bar of iron placed across from limb to limb a short distance back from the poles would act as a shunt to the armature and would divert to itself part of the lines of force which would otherwise go through the armature and would weaken the attraction of the magnet for the latter. In dynamos a bar of iron used as a magnetic shunt has been used to diminish the lines of force going through the armature and hence to weaken the field and diminish the electro-motive force. By moving the shunt nearer or further from the poles the dynamo is regulated.

In the cut the projections between the yoke and poles of the magnet shown act as a shunt to the yoke, taking some lines of force therefrom.

Fig. 225. MAGNETIC SHUNT.

Magnetic Storms. Terrestrial magnetic disturbances sometimes covering very wide areas, and affecting the magnetic declination and inclination. One such disturbance was felt simultaneously at Toronto, Canada, the Cape of Good Hope, Prague and Van Diemen's Land. (Sabine.)

354 STANDARD ELECTRICAL DICTIONARY.

Magnetic Strain. The strain produced by magnetic lines of force in substances exposed to their action. It is observed in substances placed between the poles of a strong electro-magnet, and evinces itself in the alteration of the optical properties of transparent substances.

Magnetic Stress. The stress produced by magnetic lines of force on substances through which they pass, evidenced in alteration of the optical properties of transparent bodies thus treated.

Magnetic Susceptibility. The specific intrinsic susceptibility of any material for magnetic induction. It refers to the particle of matter, and not to the mass, as in the latter its own particles react on each other and bring about what is termed permeability, q. v. (See also Magnetization, Coefficient of Induced, and Magnetic Induction, Coefficient of.)

Synonym--Coefficient of Induced Magnetization.

Magnetic Tick. When a bar of iron is suddenly magnetized or demagnetized it emits a slight sound, called the Page sound, or the magnetic tick. This has been utilized in a telephone by Reiss. The telephone will receive sound, but is very weak. It consists of a bar surrounded with a coil of insulated wire. Variations in current produce sounds, which may be articulate if the currents are produced by a telephonic transmitter.

Magnetic Twist. A bar of iron held in the magnetic meridian and pointing to the pole and twisted becomes to some extent permanently magnetized. Conversely a bar when magnetized seems to have a twist set up in it. The latter is magnetic twist.

Magnetic Variations. Changes in the value of magnetic declination or inclination. (See Magnetic Elements.)

Magnetism, Ampére's Theory of. A theory accounting for magnetic phenomena by assuming the existence of currents circulating around the molecules of permanent magnets. If such currents so circulate and all in the same direction, the result is the same as if the body of the magnet was enveloped in currents representing those of an electro-magnet or solenoid. This is because in the interior the current around one molecule would counteract the current around its neighboring ones in part, so that the only virtual currents left would be represented by those on the outer surfaces of the outer shell of molecules, and these virtually resolve themselves into one general current sheet, surrounding the magnet and coinciding with its surface.

The theory assumes that such currents permanently circulate around the molecules of paramagnetic substances. Under ordinary conditions there is no coincidence in their direction and no resultant current is produced. When magnetized or polarized the molecules are brought into order, so that the direction of their current coincides and the body becomes a magnet.

355 STANDARD ELECTRICAL DICTIONARY.

Fig. 226. AMPÉRIAN CURRENTS IN MAGNETS.

At the north pole of the magnet the direction of the Ampérian currents is the reverse of that of a watch when the observer faces the pole; the reverse obtains for the south pole.

The attraction of opposite and repulsion of similar poles is explained by the actions of the Ampérian currents upon each other. If north and south pole are placed together these currents will coincide in direction and hence will attract each other. If two like poles are put together the currents will have opposite directions and will repel each other.

No energy is supposed to be required to maintain currents around or in a single molecule.

Fig. 227. NORTH AND SOUTH POLES OF A MAGNET SHOWING DIRECTION OF AMPÉRIAN CURRENTS.

Magnetism, Blue. A term arising from the two fluid theory of magnetism; the magnetism of the south pole of a magnet. (See Magnetic Fluids.) The magnetism of the north pole is termed red magnetism. Both terms originated presumably in the painting of magnets, and are little used.

Synonym--South Magnetic Fluid.

356 STANDARD ELECTRICAL DICTIONARY.

Magnetism, Components of Earth's. The magnetic force of the earth acts in the plane of the magnetic meridian and in direction generally lies oblique to the plane of the horizon. It can be resolved into two components, one vertical, which has no directive effect upon the magnetic needle, the other horizontal, which represents the directive element for the usual compass needle. For the dipping needle, q. v., the vertical component is the only active one. A magnetic needle mounted on a universal joint at its centre of gravity would be acted on by both components.

Magnetism, Creeping of. The gradual increase of magnetism when a magnetic force is applied with absolute steadiness to a piece of iron. It is a form of magnetic lag. It may last for half an hour and involve an increase of several per cent. of the total magnetism.

Synonym--Viscous Hysteresis.

Magnet, Iron Clad. A magnet with a casing of iron connected at one end to the core. The term is generally applied to electromagnets of this form.

Synonyms--Tubular Magnet--Jacketed Magnet.

Magnetism, Decay of. The gradual loss of magnetism by permanent magnets, due to accidental shocks, changes of temperature, slow spontaneous annealing of the iron and other similar causes.

Magnetism, Discharge of. The loosing of magnetization. Thus in a shunt-wound dynamo there is a critical resistance for the outer circuit, below which the field ceases to be magnetized, as enough current ceases to be shunted into it to magnetize it. The machine is said to unbuild itself, and a discharge of magnetism occurs from the field magnet.

Magnetism, Ewing's Theory of. Ewing found by a model consisting of a number of pivoted magnetic needles that the observed phenomena of magnetization could be represented thereby. Thus there would be no need of assuming internal frictional forces of Maxwell, nor the closed rings or chains of Hughes. The theory retains the notion, however, of paramagnetic matter, consisting of an assemblage of molecular magnets. The loss of energy by hysteresis is represented in the model by the energy lost by the needles in beating against the air.

357 STANDARD ELECTRICAL DICTIONARY.

Magnetism, Free. The magnetism or magnetic field outside of a magnetic circuit. It is due to escape of lines of force and to the magnetic leakage through the air. The lines of force are never, under the most favorable circumstances, confined to the metallic circuit of the magnet and armature. In a simple magnet without armature all the lines of force have to follow an air path, and the field is at its strongest. As the magnetism is strongest at the surface near the poles, the term is sometimes understood as applying to the surface attraction. In such case it is defined as the distribution, on a magnetized bar or mass, of magnetic lines of force as they emerge from its surface.

Synonym--Surface Magnetization.

Magnetism, Hughes' Theory of. A theory accounting for magnetic phenomena by assuming that each molecule is a magnet, and that in a polarized or magnetized body they are all arranged with their poles in the same direction, while in an unmagnetized body their poles, alternating in direction, neutralize each other.

Magnetization consists in a partial rotation of the molecules so as to make them agree in position, thus, as a resultant developing north and south poles at the ends of the bar.

The theory is in a certain sense simpler than Ampere's theory, but is not so generally adopted.

Magnetism, Lamellar Distribution of. The distribution of magnetism in thin and uniform or "simple magnetic shells," q. v. A given distribution is termed lamellar if the substance in which it exists can be divided into simple magnetic shells, which either form closed surfaces, or have their edges in the surface of the substance. In lamellar distribution the polar area is very large compared with the distance between opposite poles.

Magnetism of Gases. Faraday experimented on this point by coloring gases with a little vapor of iodine or other colored gas, and letting them flow between the two poles of a powerful electromagnet. In this way he found some are repelled, some attracted, and in the case of oxygen, it is attracted at one temperature and repelled at another. At ordinary temperatures a cubic yard of oxygen possesses the magnetism of 5.5 grains of iron and when liquefied it is strongly attracted.

Magnetism or Magnetization, Temporary. When a mass of iron is magnetized by a current, when the current ceases the portion of its magnetism which disappears is the temporary magnetism; the portion retained is the residual or permanent magnetism.

Magnetism, Red. A term arising from the two fluid theory of magnetism; the magnetism of the north pole of a magnet. (See Magnetic Fluids.) The magnetism of the south pole is termed blue magnetism. Both terms originated in the painting of magnets. They are but little used.

Synonym--North Magnetic Fluid.

358 STANDARD ELECTRICAL DICTIONARY.

Magnetic Remanence. The residual magnetism left in a bar of steel or other paramagnetic material after the application of a powerful magnet. It is distinguished from coercive force, as the latter is the amount of negative magnetizing or of demagnetizing force required to reduce the remanent magnetism to zero.

Synonym--Remanence--Residual Magnetism.

Magnetism, Solenoidal Distribution of. The distribution of magnetism in such a way that the poles are very far apart in proportion to their area. The magnetization of a long thin bar of steel illustrates solenoidal distribution.

Magnetism Sub-permanent. The magnetism of a paramagnetic substance which presents a considerable degree of permanency, but which gradually disappears, leaving the permanent magnetism present. It is noticeable in iron or steel ships whose magnetism gradually reduced in quantity, eventually becomes fully permanent.

Magnetism, Weber's Theory of. The molecules of a magnetizable material by this theory are supposed to be magnets with their poles lying in every direction, and hence neutralizing each other. By magnetization these are supposed to be turned with their similar poles in the same direction, and their axis parallel, hence acting like a group of magnets. It is practically identical with Hughes' theory.

Magnetism, Terrestrial. The magnetism of the earth. (See Magnetic Elements.)

Fig. 228. MAGNETIZATION BY DOUBLE TOUCH.

Magnetization by Double Touch. The process of magnetizing a steel bar by simultaneously stroking it with two poles of a horseshoe magnet or with two opposite poles of two bar magnets. The poles must be close but not touching. A block of wood may be placed between the ends if single magnets are used. The poles are placed on the middle of the bar and carried back and forth to one end, then to the other, and so on, ending at the middle of the bar in such direction as to give each end the same number of strokes. The poles must be close together or consequent poles will be produced. If bar magnets are used they may be held inclined at an angle of 15º to 20º with the horizontal bar to be magnetized. The ends of the latter may rest on poles of two other magnets, each end on a pole of the same name as that of the magnetizing magnet on its side. (See Magnetization, Hoffer's Method.)

359 STANDARD ELECTRICAL DICTIONARY.

Magnetization by Separate Touch. A method of magnetization. Two magnets are used. Held in an inclined position two opposite poles are touched to the bar near its centre, and are drawn off to the two ends. They are returned through the air and the process is repeated.

Magnetization by Single Touch. A method of polarizing or magnetizing steel bars, by stroking them always in one direction with one pole of a magnet, returning it through the air. The stroking is best done on both sides. The stroking may begin at one end and end at the other, or it may be commenced in the center of the bar and be carried to one end with one pole, and the same done for the other half with the other pole.

Magnetization by the Earth. The earth imparts magnetism to iron masses. If a rod of steel is held parallel to the inclination and in the magnetic meridian it exhibits polarity, which by jarring or hammering, can be made to some extent permanent. A piece of soft iron held vertically, or still better in the line of the dip as above, and which is twisted when in that position, becomes magnetized with some degree of permanence. Many other instances are cited, such as fire-irons, lamp-posts, iron gates, lathe turnings, all of which often exhibit polarity, having been magnetized by the earth's field.

[Transcriber's note: The earth's magnetic field is believed to originate it electric currents in the moving molten core.]

Magnetization, Coefficient of Induced. The coefficient (q. v.) expressing the relation between the specific intensity of magnetization of a particle and the magnetizing force. The magnetizing force is measured by the lines of force it can produce in a field of air. The coefficient of induced magnetization is the factor by which the intensity of a magnetizing field must be multiplied to produce the magnetization imparted by it to a particle of any substance. This coefficient varies for different substances, and is also called magnetic susceptibility. It is distinguished from permeability as referring only to a particle isolated from influence of a mass of surrounding particles of its own kind. It is definable as the intensity of the magnetization assumed by an exceedingly long and exceedingly thin bar placed in a unit field. If a mass of metal were placed in such a field all its particles would become affected and within the mass no unit field could exist. Hence magnetic susceptibility (another name for this coefficient) does not apply to the case of large cores of electro-magnets and dynamo-armatures, but is really a theoretical rather than a practical figure.

The sign of the coefficient of diamagnetic bodies is negative; of paramagnetic bodies is positive.

Synonym--Magnetic Susceptibility. \

360 STANDARD ELECTRICAL DICTIONARY.

Magnetization, Cycle of. A cycle of positive or of positive and negative magnetization represents the application of a magnetizing force beginning at a fixed value, generally zero, rising to a maximum, or to a value of maximum distance from the initial and then returning to the original basis. It is virtually a full wave of magnetization and may extend on both sides of a zero line giving positive and negative values.

Cycles of magnetization apply especially to transformers and other apparatus of that character used with the alternating current system.

Magnetization, Hoffer's Method. For horseshoe bars an armature is placed against the poles of the magnet bar to be treated. The poles of a strong horseshoe magnet are stroked over it from poles to bend and returned through the air, or vice versa. In the first case the poles will be the same as those of the inducing magnet; in the second case they will be opposite. A maximum effect is produced in ten strokes. The stroking should be applied to both sides. An electro-magnet may be used as inducer as shown, but an armature should be used; in the cut it is omitted.

Fig. 229. MAGNETIZING A HORSESHOE MAGNET.

Magnetization, Intensity of. The amount of magnetism induced in or present in a body. It is expressed in Magnetic Lines of Force, q. v., per cross-sectional area.

Magnetization, Isthmus Method of. A method used by Ewing in a research on the magnetization of iron in very strong fields. He used samples of iron turned down in the centre to a narrow neck, and thus concentrated the lines of force greatly.

Magnetization, Elias' Method. The bar to be magnetized is surrounded by a magnetizing coil, q. v. A strong current is passed through it, and the coil is moved back and forth a few times.

Magnetization, Jacobi's Method. For horseshoe bars. The bar is placed with its poles against those of a horseshoe magnet. A bar of soft iron, long enough to reach from outside to outside of the legs, is laid across near the junction and is drawn along towards the bend of the new bar and away from it. This is repeated a few times on both sides.

361 STANDARD ELECTRICAL DICTIONARY.

Magnetization, Limit of. As the induction of magnetizing force increases, magnetization of paramagnetic metals tends towards a limit, the increase in magnetization being continually less and less as the metal becomes more highly magnetized. In diamagnetic substances no limit is discernible.

Synonym--Maximum Magnetization.

Magnetization, Specific. The magnetic moment per gram of a substance.

Magnet-keeper. A bar of iron connecting the two poles of a permanent magnet. Often the same bar serves as armature and keeper.

Magnet, Lamination of. It is advantageous to make magnets of laminated construction, or of thin plates of steel. The thin metal can be better tempered or hardened than thick metal. A slight separation of the plates is advantageous from some points of view. If in actual contact there is some danger that the weaker members will have their polarity reversed by the stronger ones. This is counteracted to some extent by separation.

Magnet, Long Coil. A high resistance electro-magnet; one whose coil is of thin wire of considerable length.

Magnet, Natural. The lodestone, q. v.; a variety of magnetite or magnetic oxide of iron, exhibiting permanent magnetism, attracting iron, and possessing north and south poles.

Magnet, Neutral Line of. A line at right angles to the magnetic axis of a magnet, q.v., and nearly or quite at the centre, so situated with reference to the poles on either end that it marks the locus of no polarity. It has been called the equator of the magnet. It is defined by the intersection of the plane of no magnetism with the surface of the bar.

Synonym--Magnetic Equator.

Magnet, Normal. A bar or compound bar magnet, magnetized to such an extent that the curves of the lines of force run into each other in the middle, is thus termed by Jamin.

Magneto. Abbreviation for Magneto-electric Generator. (See Magneto-electric Generator.)

Magneto Call Bell. A call operated by current from a magneto-electric generator. It is very generally used in telephone systems.

362 STANDARD ELECTRICAL DICTIONARY.

Magneto-electric. adj. Relating to induced electric effects due to the cutting of true magnetic lines of force by, or equivalent action of or upon a conductor. These effects are identical with electro-magnetic effects and are only distinguished from them by the field being due to a permanent magnet instead of an electromagnet.

Magneto-electric Brake. A device for bringing to rest an oscillating galvanometer needle. It consists essentially of a coil in circuit with a key and with the galvanometer. On opening the circuit an inverse current is established by induction, tending to bring the needle to rest.

Magneto-electric Generator. A current generator operating by maintaining a potential difference at its terminals, by reactions in a field of force, which field is established by a permanent magnet.

The cut, Fig. 230, shows the general principle of construction of a direct current generator. The armature is rotated between the poles of a permanent magnet. Any of the regular types of dynamo armature can be used. From its commutator the current is taken by brushes.

Fig. 230. MAGNETO-ELECTRIC GENERATOR.

Fig. 231. MAGNETO-ELECTRIC GENERATOR.

363 STANDARD ELECTRICAL DICTIONARY.

The cut, Fig. 231, shows an alternating current machine. In it a pair of bobbins, wound in series, and both either right-handed or left-handed, are rotated between permanent magnet poles. The current may be taken off by two brushes bearing on two collecting rings on the axis of the bobbins, the ends of the wire being connected thereto. Or if a shocking current is desired, one of the brushes or springs may strike a series of pins forming virtually a broken or interrupted collecting ring. This gives a current for medical purposes.

Synonyms--Magneto-dynamo--Magneto-electric Machine.

Magnetograph. An apparatus for recording variations in magnetic elements. One type includes a magnetic needle to which a concave mirror is attached. The light ray from the mirror is reflected upon sensitized paper where its movements are photographically reproduced. The movements of the spot are due to the movements of the needle and act as the record of the same.

Magneto-Inductor. An instrument for use with a ballistic galvanometer to reproduce a definite current impulse. Two magnets are fastened together in one straight line, the north poles almost touching. This is mounted at the end of a rod like a pendulum, the axis of the magnets transverse to the rod. The magnets are carried by a frame and oscillate at the end of the rod, back and forth within a fixed coil, which is one-half the length of the double magnet. A bob is attached to the bottom of the frame by which the whole can be swung. As the magnets are of fixed value, their time of oscillation constant, and the coil fixed in size, the apparatus provides a means of getting a definite instantaneous current of identical value whenever needed.

Fig. 232. MAGNETO-INDUCTOR.

364 STANDARD ELECTRICAL DICTIONARY.

Magnetometer. (a) A reflecting galvanometer, with heavy magnetic needle, dampened by a copper frame. It was devised by Weber.

(b) An apparatus for measuring the intensity of magnetic force. It may consist of a magnet suspended by bifilar or by torsion suspension. A reflecting mirror and scale as in the reflecting galvanometer may be used to act as indicator of its motions. It is used in investigations of the intensity of the earth's field.

If the motions of the spot of light are received on a moving strip of sensitized paper and are thereby reproduced photographically, the instrument is self-recording. Such an apparatus is used in the Kew Observatory, Eng., for recording the terrestrial magnetic elements.

Magnetometry. The determination of the magnetic moment of a magnet.

It involves the determination by experiment of--( a) the product of the magnetic moment, M, of the magnet by the horizontal component, H, of the earth's magnetism; (b) the quotient of M divided by H. Knowing these two quantities, M is given by the formula M = SquareRoot( )M * H) * (M/H) ) and if desired H is given by the formula H = SquareRoot( (M*H) / (M/H)).

M*H is determined by the method of vibrations. A very long, thin magnet suspended by a torsion filament is caused to oscillate, and its period is determined. Calling such period T and the moment of inertia of the magnet I, we have the formula T= 2* PI * SquareRoot( I / (H*M) ) (a), whence H*M is calculated, I of course being known or separately determined.

Fig. 233 END-ON METHOD.

Fig. 234. BROADSIDE METHOD.

M/H is determined by the End-on deflection method, or the Broadside deflection method. In both cases the deflection of a compass needle by the magnet in question is the basis of the work.

In the end-on method AB is the magnet under examination; DE the compass needle; a the angle of deflection; d the distance between C and the middle of AB, which should be considerable compared with the length of DE; 2l, the length of AB. We then have the formula tan a = (M/H) * (2d / (d^2 - l^2)^2), which if 2l is small compared to d reduces to tan a = M/Hd 3

(b), which gives M/H, a and d being known.

365 STANDARD ELECTRICAL DICTIONARY.

In the broadside method the line d is the magnetic meridian, and the diagram shows the relative positions. We then have the formula tan a = (M/H) / (d2 + l2)^1.5; which if 1 is relatively small reduces to tan a = M/(H * d3 )(C.)

[Transcriber's note: The image of the above paragraphs is included here.]

a and c or a and b can be combined giving M and H in C.G.S. measurement.

Magnetometer, Differential. An apparatus, invented by Eickemeyer, for testing the magnetic qualities of different samples of iron. It is very similar in construction and principle to the magnetic bridge, q. v.

Magneto-motive Force. The force producing a magnetic field or forcing lines of force around a magnetic circuit. It is usually applied only to electro-magnets and is expressible in turns of the wire winding multiplied by amperes of current, or in ampere-turns.

Magnet Operation. A term in surgery; the use of the electro-magnet or permanent magnet for removing particles of iron from the eye.

Magnetoscope. An apparatus for detecting the presence of magnetism, without measuring its intensity. A simple magneto-scope consists of a magnetized bit of watch-spring suspended in a vertical glass tube by a fine filament. A bit of unmagnetized soft iron wire may be used in the same way. The first has the advantage of indicating polarity; the latter merely shows magnetic attraction. A cork may be used as base of the instrument.

Fig. 235. MAGNETOSCOPE.

366 STANDARD ELECTRICAL DICTIONARY.

Magnet, Permanent. A bar of steel charged with residual magnetism. Steel possesses high coercive force in virtue of which when once magnetized it retains part of the magnetization.

Permanent magnets are generally straight bars or U shaped; they are termed bar magnets, magnetic needles, horseshoe magnets, machine magnets and otherwise, according to their shape or uses.

Magnet Pole. The part of a magnet showing strongest polarity; the part which attracts iron the most powerfully, and acts as the starting point for lines of force.

Magnet Poles, Secondary. Magnet poles are often not situated at the ends. Owing to inequality of the material or other causes they may occupy intermediate positions on the magnet. Such poles are called secondary poles.

Magnet Pole, Unit. A unit magnet pole is one which exerts unit force on another unit pole placed at unit distance from it. Unit force is the dyne; unit distance is one centimeter.

Magnet, Portative Power of. The power of sustaining a weight by attraction of its armature possessed by a magnet. In general terms the adherence of the armature of a magnet to the pole varies with the square of the number of lines of force which pass through the point of contact. Hence an increased adherence of the armature to a horseshoe electro-magnet is sometimes obtained by diminishing the area of contact of one pole which concentrates the lines of force. Steel magnets were frequently made with rounded ends to increase the portative power.

Magnet, Simple. A magnet made of one piece of metal, or at least magnetized as such; the reverse of a compound magnet, which is magnetized piece by piece and then fastened together.

Magnet, Solenoidal. A magnet which is so uniformly magnetized and is so long in proportion to its other dimensions that it virtually establishes two magnetic poles, one at either end. It is a long thin bar so magnetized that all its molecules would, considered as magnets, be absolutely equal. (Daniell.) It acts like a solenoid, except that it is longer in proportion than the solenoid generally is constructed.

Magnet, Sucking. A magnet coil with movable or loose axial bar of soft iron.

The whole is usually mounted vertically. When a strong enough current is passed the bar is drawn up into the coil as if by suction, whence the name.

367 STANDARD ELECTRICAL DICTIONARY.

Magnet, Unipolar. No such thing as a unipolar magnet is possible. The name is given to poised or suspended magnets, one of whose poles lies in the axis of suspension. It is obvious that such a magnet will act, as far as its directive tendency and rotatory movements are concerned, as if it had only one pole. As shown in the cut, the pole s in both magnets lies in the axis of suspension or directly under the filament by which they are suspended, while the other pole n is the active pole in causing rotation or directive tendency; c c are counterweights or counterpoises.

Fig. 236. UNIPOLAR MAGNETS.

Magnetophone. An apparatus for producing a loud sound, involving the principles of the telephone. A rapidly alternating or make and break current being produced by any means and being transmitted through the telephone gives a loud note of pitch dependent on the current producing it. Sometimes a perforated metallic disc is rotated in a magnetic field, and produces the requisite type of current.

Magnus' Law. A law of thermo-electricity. In a homogeneous circuit, however, the temperature varies from point to point; there is no current.

Whatever potential differences may be established by the variations in temperature it is evident that they must counteract each other and reduce to zero.

Mains, Electric. The larger conductors in a system of electric light or power distribution.

Make. v. To complete a circuit, as by closing a switch.

Make and Break Current. A current which is continually broken or interrupted and started again. It is applied only where the "makes" and "breaks" succeed each other with great rapidity, as in the action of an induction coil or pole changer, etc. It has had considerable importance in litigation affecting the Bell telephone patents, the courts holding that the original Bell patent (No. 174,465, of 1876,) covered the undulating current, for the transmission of speech. Many efforts have been made by litigants to prove that specific telephones have transmitted articulate speech by the make and break current, but without success. If this could have been proved the assumption is that the courts would have sustained the use of such device as not infringing upon the claims of the Bell patent.

Malapterurus. A fish, sometimes called the thunder fish, an inhabitant of African rivers, occurring in the Nile and Senegal. It possesses considerable electric power, similar to that of the gymnotus and torpedo, although inferior in amount.

368 STANDARD ELECTRICAL DICTIONARY.

Fig. 237. MALAPTERURUS.

Man-hole. The cistern-like depression in the ground for giving access to the ends of tubes in electric conduits. (See Conduit, Electric Subway.)

Marked End or Pole. The north pole or north seeking pole of a magnet, so called because it is usually marked with a notch or scratch by the maker. The south pole is called the unmarked end.

Mass. The quantity of matter in a body. The C. G. S. unit of mass is the quantity of matter in a gram. While weight varies with latitude and other circumstances, mass is invariable.

The unit of mass is also defined as the quantity of matter which in a balance will counterpoise a standard mass, the gram or pound. As the gram is intended to be the mass of one cubic centimeter of water at 3.09º C. (39º F.), the C. G. S. unit of mass is really 1.000013 gram.

As a primary unit its dimensions are indicated by M.

Mass, Electric. A term for quantity of electricity. The unit mass is such a quantity as at unit distance will act with unit force.

Matter, Electric. The imaginary substance constituting electricity; a conception used purely as a matter of convenience.

[Transcriber's note: The electron was discovered five years after this publication.]

Matter, Radiant. Matter in the ultra-gaseous or so-called fourth state. In the gaseous state the molecules of a gas are in perpetual kinetic motion, colliding actually or virtually with each other, rebounding from such approach, and striking also the walls of the containing vessel. But except for these deflections, which are of enormous frequency, the paths of the molecules would be perfectly straight.

In the radiant state matter exists in so high a vacuum that collisions of the molecules rarely occur, and the molecules simply beat back and forth in straight lines from side to side of the containing vessel.

A layer of gas in this condition is termed a Crookes' layer, from Prof. William Crookes, who discovered and investigated these phenomena.

369 STANDARD ELECTRICAL DICTIONARY.

Luminous streams of the molecules are produced by electric high potential discharges between electrodes. The course of the discharge is normal, in general terms, to the surfaces of the electrodes, and reaches from one to the other in a curve or straight line, as the case may be.

These luminous streams are deflected by a magnetic field; if brought to a focus can heat refractory material in that focus to a full white heat, and can develop phosphorescence. The latter is termed electric phosphorescence. A great variety of experiments have been devised to illustrate the phenomena of radiant matter. The vacuum is generally produced in a hermetically sealed glass vessel into which the electrodes are sealed, and which contain the phosphorescent substances or other essentials for the experiments. The vessels are termed Crookes' Tubes.

[Transcriber's note: Crookes reported on "radiant matter" in 1879. It is actually electrons, but he failed to distinguish them from ordinary atoms. Thompson properly described electrons in 1897.]

Matteueci's Experiment. An experiment for showing the inductive effect of the discharge of a Leyden jar. Two glass plates are supported on standards in a vertical position. Flat coils of wire are wound or coiled and secured to one surface of each plate. One plate has much finer and longer wire than the other. Metal handles are connected to the ends of the coarser wire coil. The plates are placed with their coils facing each other. A Leyden jar is discharged through the coarser coil, while the handles are grasped by a person. The shock of the discharge is felt by him.

Matting, Electric Floor. Matting or floor covering underlaid with burglar alarm contacts, so arranged as to be closed by anyone walking on the matting. The contacts are connected to a burglar alarm system. The object is to provide an alarm if a burglar enters a house, in case he should enter a door or window without sounding the bell. The latter can be done by cutting out the window or part of the door instead of opening it.

Maxwell's Theory of Light. A theory of light. It is due to J. Clerk Maxwell.

It supposes the phenomena of electric induction to be due to the ether, q. v. It supposes the condition of the ether when conveying light to be the same as if exposed to the induction of rapidly alternating currents or discharges (in this case synonymous). It therefore is an electro-magnetic effect if the theory is correct.

An electric stress such as one due to the induction of an electrostatically charged body is not a wave-creating element or factor, but is a simple stress. But let this stress be stopped and renewed and at once it appears as a wave-forming agency.

This stoppage and renewal represents evidently a discharge succeeded by a charge, or if repeated is equivalent to an intermittent current or an alternating one.

370 STANDARD ELECTRICAL DICTIONARY.

Again the electrostatic stress kept constant may by being carried through space carry with it a wave, just as a moving projectile carries a wave of air in advance of itself.

Admitting this much the following consequences follow:

Since in non-conductors the displacement produces a restitution force, which varies as the displacement which is requisite or is a criterion for the propagation of waves, while in conductors no such force is manifested and the electric energy appears as heat, it follows that light vibrations are not possible in conductors, because electro-magnetic waves do not exist in them when they are in circuit, and conductors should be opaque, while the reverse is true for non-conductors. (Daniell.)

This is carried out often enough to make a striking evidence in favor of Maxwell's theory.

The velocity of propagation of an electro-magnetic disturbance in a non-conductor should be equal to that of light. This constant is proved by mathematical considerations, to be approximately the same as the ratio of the electrostatic to the electromagnetic unit of intensity or quantity. This ratio is 3E10 (30,000,000,000), which is almost exactly the velocity of light.

It also follows from what has been said that if an electrostatically charged body were whirled around a galvanometer needle at the rate of 3E10 revolutions per second it should affect it like a circulating current. This rate of rotation cannot be attained, but Rowland has made manifest the effect of a rotating statically charged body upon a magnetic needle.

The above is the merest outline of Maxwell's theory. The full development must be studied in his own and succeeding works.

Mayer's Floating Magnets. An experiment due to Prof. Mayer. A number of sewing needles are magnetized and thrust into bits of cork, almost all the way through, with their like poles projecting. They are floated in a basin of water and take, under the effects of attraction and repulsion, when approached by a magnet pole, regular geometric positions, marking out the positions of angles of polygons.

Measurements. The determination of the value of quantities; determination of the factor by which the unitary value must be multiplied to produce the quantity under examination. Such are the measurement of the voltage of a galvanic battery, or of the ohms of resistance of a conductor. Electricity has been termed the science of measurement.

Meg or Mega. A prefix, meaning one million times. A megohm is one million ohms; a megerg is one million ergs; a megadyne is one million dynes.

371 STANDARD ELECTRICAL DICTIONARY.

Fig. 238. MAYER'S FLOATING MAGNETS.

Mercury. A metal; one of the elements; symbol, Hg; atomic weight, 200 ; equivalent, 200 or 100; valency, 1 and 2. It is a conductor of electricity. The following data are 0º C. (32º F.) Relative Resistance, 62.73 Specific Resistance, 94.32 microhms. Resistance of a wire, (a) 1 foot long, weighing 1 grain, 18.51 ohms. (b) 1 foot long, 1/1000 inch thick, 572.3 " (c) 1 meter long, weighing 1 gram, 12.91 " (d) I meter long, 1 millimeter thick 1.211 " Resistance of a 1 inch cube, 37.15 microhms. Percentage increase of resistance per degree C. 1.8° F. at about 20° C. (68° F.), .72 per cent. Electro-chemical equivalent (Hydrogen = .0105), 2.10 mgs. 1.05 "

372 STANDARD ELECTRICAL DICTIONARY.

Mercury Cup. A cup of iron, wood or some material that does not amalgamate or is unattacked by mercury, which is filled with mercury and made an electrode of a circuit. By dipping the other terminal of the circuit into the mercury a very good contact is obtained. It is well to cover the mercury with alcohol. The cup may be filled so that the mercury rises in a meniscus or semi-globule above its edges.

For some purposes this form is useful, as for contacts with the end of a swinging wire or pendulum, because in such cases the contact can be made without the contact point entering the cup. The point swings through the projecting meniscus without touching the edges of the cup. A mercury cup and contact constitute a mercury break.

Meridian, Astronomical. The great circle passing through the north and south poles of the celestial sphere. It lies in a plane with the corresponding geographical or terrestrial meridian.

Meridian, Geographic. The true north and south meridian; the approximate great circle formed by the intersection of a plane passing through north and south poles of the earth with the earth's surface.

373 STANDARD ELECTRICAL DICTIONARY.

Fig. 239. SCHALLENBERG'S ALTERNATING CURRENT METER.

Meter, Alternating Current. A meter for measuring alternating current, as supplied to consumers, from an alternating current system. Like most commercial meters its only function is the measurement of quantity; the potential difference is maintained at a constant figure by the generating plant.

The cut shows the Schallenberg meter. It is simply an alternating current motor (see Motor, Alternating Current), with air vanes mounted on its spindle. A main coil passes all the current. Within this is a second coil complete in itself, and not touching or connecting with the other. The latter is built up of copper rings. Within the two coils, and concentric with both is a disc of copper carried by a vertical spindle. The same spindle carries air vanes, and is free to rotate. As it does so it moves the indicating machinery.

The current in the outer coil induces one in the inner coil. Owing to lag, the current in the inner one differs in phase from that in the outer one, and a rotatory field is produced. The copper disc acquires induced polarity, and rotates with speed which normally would be in proportion to the square of the current. But the object of the meter is to register the current only. The air vanes effect this. The resistance of the air to their motion causes the rate of rotation to vary directly as the speed.

Meter Bridge. A form of Wheatstone's bridge in which one lateral pair of arms is represented by a straight wire. The other pair comprise a known resistance, and the resistance to be determined. The galvanometer is connected on one side between the known and unknown resistance. On the other side its connection is moved back and forth along the straight wire until the balance is secured and the galvanometer reads zero.

The relative lengths of wire intercepted between the two ends thereof and the movable galvanometer connection are proportional to the resistance of these parts and give the necessary data with the one known resistance for determining the unknown resistance.

374 STANDARD ELECTRICAL DICTIONARY.

In the original meter bridge the wire was one meter long, whence its name, and was stretched straight. In more recent examples the wire varies in length and in one form is bent into a circle or spiral, so as to make the instrument more compact.

The contact is not a sliding one, but is adjusted by trial. The contact piece is slid along, but not touching the wire, and from time to time is pressed down against the wire. This prevents wear of the wire. The wire may be made of platinum or of platinum-iridium alloy. The latter is very hard and not easily worn out.

Sometimes, as shown in the cut, three parallel wires are stretched along the baseboard of the instrument, and arranged so that a single wire, two wires or three wires in series can be used for the proportional sides of the bridge, thus making it a two-meter or three-meter bridge as desired. On the other hand some are made of restricted length, as a half or quarter meter only.

Fig. 240. METER BRIDGE.

In the cut J K is the wire, traversed by the contact key. By moving the contact C back and forth in the slot it can be brought over any of the three divisions of the wire. H is the handle for depressing the key. S is a flat spring, carrying the contact piece and holding it up from the wires, except when pressed downwards. As shown in the cut, it is in use for calibrating a voltmeter V, by Poggendorff's method, G being the galvanometer and r1 and r2 being resistances.

Synonyms--Slide Bridge--Slide Balance.

Meter Candle. A unit of illuminating power; the light given by one standard candle at a distance of one meter. The ordinary units of illuminating power are altogether relative; this one is definite.

375 STANDARD ELECTRICAL DICTIONARY.

Meter, Chemical Electric. A current meter in which the current is determined by the amount of chemical decomposition which it can effect. In the Edison meter the solution is one of zinc sulphate. Two electrodes of zinc are immersed in it, and a fractional part of the current is passed through it. The gain in weight of one electrode and the loss in the other are proportional to the current. Both electrodes are weighed periodically, one acting as check upon the other.

Meter, Current. An instrument for measuring the quantity of electricity in current form supplied to consumers. It may be of various types. The general principle involved is that in commercial installations for incandescent light and power supply a fixed potential is usually maintained, the multiple arc system being employed. Hence all that is requisite is to measure the coulombs or the ampere-hours to know what quantity of energy has been supplied.

Meter, Electro-magnetic. A current meter in which the current is measured by its electro-magnetic effects.

Meter-millimeter. A unit of resistance. (See Resistance, Meter-millimeter.)

Meter, Thermal Electric. A current meter in which the current is measured by the heat it imparts to a conductor. In one meter a very light helix of mica is poised horizontally over a conductor, and the whole is enclosed in a case. As the wire is heated it causes an ascending current of air which rotates the vane, and the latter moves delicate clockwork which moves indicating hands. The hotter the wire the more rapidly the air ascends, and consequently the speed of the vane is proportional to the current, because the heat of the conductor is proportional thereto.

Meter, Time Electric. An electric meter which measures the length of time during which current is used. It assumes a constant current and potential. It is virtually a clock, which is turned on when the current passes, and is turned off with the current.

Meter, Watt. A combined current and potential meter. It is constructed on the general lines of a Siemens' Electro Dynamometer. If in it one coil is made of coarse wire and is placed in series with the current conductor, and if the other is wound with fine wire and is connected as a shunt from point to point whose potential difference is to be determined, the instrument becomes a watt meter.

Synonym--Energy Meter.

Methven Standard or Screen. A standard of illuminating power. It is the light emitted by a three-inch Argand gas flame through a rectangular aperture in a silver plate carried by a screen. The aperture is of such size and so far distant from the flame as to permit the passage of exactly two candles illuminating power.

Fig. 241. METHVEN SCREEN

376 STANDARD ELECTRICAL DICTIONARY.

Mho. A unit of conductance, not in very general use. It is the reciprocal of the ohm. Thus a resistance of ten ohms is a conductance of one-tenth mho.

Mica. A natural mineral, a silicate of several oxides; muscovite. It is used as an insulator and dielectric. Its resistance per centimeter cube after several minutes electrification at 20º C. (68º F.) is 8.4E13 ohms (Ayrton). Its specific inductive capacity is 5, air being taken at 1.

Mica, Moulded. An insulating material, whose body is made of mica pulverized and cemented together with heat and pressure and some suitable cement. Shellac is often used as the cement.

Micro. A prefix meaning "one-millionth of;" a micro-farad is one-millionth of a farad.

Micrometer. An instrument for measuring small distances or small differences. It generally is based upon an accurate screw which may have a worm wheel for head, actuated by a worm or helix with graduated head, so that exceedingly small advances of the screw may be produced. The pitch of the screw being known its actual advance is known.

Micrometer, Arc. A micrometer for measuring the distance between voltaic arc electrodes.

Micron. A unit of length. It is one-millionth of a meter or four one-hundred-thousandths of an inch.

377 STANDARD ELECTRICAL DICTIONARY.

Microphone. An apparatus which includes a contact of variable resistance; such resistance can be varied in amount by slight vibrations, such as those produced by sound waves. The apparatus in use forms part of a circuit including a telephone and current generator. As the contact is varied the resistance of the circuit and consequently the current intensity changes and sounds are emitted by the telephone corresponding to such changes. If the microphone is spoken to, the telephone will emit corresponding sounds, reproducing the voice.

It has been found in practice that carbon gives the best microphone contact. One of the simplest and earliest forms is shown in the cut. A short rod or pencil of carbon, A, such as used in batteries, is sharpened at the ends and rests loosely in a vertical position between two blocks of carbon, C C, in each of which a hole is drilled to receive one of the points. The blocks are carried on a standard and base D. The blocks are connected with two terminals x, y, of a circuit, including a telephone and battery. There are two contacts to be disturbed.

If delicately adjusted a fly walking over the base-board will disturb the contacts enough to produce sounds in the telephone. These sounds are possibly not due only to sound waves, but in part to absolute mechanical disturbances.

The various forms of telephone transmitter are generally microphones.

Fig. 242. MICROPHONE.

Microphone Relay. A combined microphone and telephone. A microphone is placed close to the diaphragm of a telephone. The slight sound waves emitted by the telephone affect the microphone and are repeated in its circuit. The microphone circuit includes a local battery and telephone.

Microtasimeter. An apparatus for indicating minute changes in temperature or atmospheric moisture.

378 STANDARD ELECTRICAL DICTIONARY.

A button of compressed lampblack is placed in series with a battery and galvanometer. A strip of some substance, affected in its length either by heat or by moisture, is held pressing against the button. A slight change in length of the strip varies the resistance of the button and hence affects the galvanometer. In this way exceedingly slight changes in heat or moisture may be indicated.

For heat indications vulcanite may be used. The heat of the hand held near it is enough to affect the galvanometer. For moisture a slip of gelatine is used. The moisture of a damp slip of paper two or three inches distant is sufficient to affect the galvanometer.

In the cut, Fig. 2, shows the general distribution of the apparatus in circuit with a battery and galvanometer. C is the base of the apparatus, from which the standard, B, with adjusting screw, H, rises. The strip of vulcanite is held between I and G. Within D is the carbon button (F in Fig. 3) pressed between G and E; A is a standard to carry the parts last described. In Fig. I it is shown as part of a Wheatstone bridge, a, b and c being resistance coils; l the tasimeter, and g the galvanometer. If a balance is secured, any variation in the resistance of the tasimeter will disturb the galvanometer.

Synonym--Tasimeter.

Fig. 243. MICROTASIMETER.

379 STANDARD ELECTRICAL DICTIONARY.

Mil. A unit of length; one-thousandth part of a lineal inch.

It is equal to .025399 millimeter; .000083 foot; .001000 inch.

Mil, Circular. A unit of area; employed in designating the cross-sectional area of wires and other circular conductors.

It is equal to .78540 square mil; .000507 square millimeter; 7.8E-7 (.00000078) square inch.

If the diameter of a wire is given in mils, the square of its diameter gives its cross-sectional area in circular mils.

Mil-foot. A unit of resistance. (See Resistance, Mil-foot, Unit of).

Mil, Square. A unit of area; one-millionth of a square inch.

It is equal to .000645 square millimeter; 1.2733 circular mil; .000001 square inch.

Milli. A prefix; one-thousandth. Thus a milligram is one-thousandth of a gram; a millimeter is one thousandth of a meter.

Milligram. A unit of weight ; one-thousandth of a gram, q. v.

It is equal to .015432 grain; .000032 troy ounce.

Millimeter. A unit of length; one-thousandth of a meter.

It is equal to 39.37079 mils; .03937 inch; .00109 yard.

380 STANDARD ELECTRICAL DICTIONARY.

Milli-oerstedt. A proposed but not adopted unit of current; one-thousandth of an oerstedt. It is equal to one-thousandth of an ampere.

[Transcriber's note: oersted: 1. CGS unit of magnetic intensity, equal to the magnetic pole of unit strength when undergoing a force of one dyne in a vacuum. 2. Formerly, the unit of magnetic reluctance equal to the reluctance of a centimeter cube of vacuum between parallel surfaces.]

mm. Contraction for millimeters.

Molar. Referring to phenomena of mass as gravitation. Mechanics generally treats of molar laws and phenomena.

[Transcriber's note: Molar, or mole, often refers to a quantity of a substance containing an Avagadro number (6.02E23) of molecules--a weight equal to the atomic weight of the molecule. For example, a mole of hydrogen (H2) is 2.015 grams; sodium chloride (NaCl) is 58.443 grams.]

Molar Attraction. The attraction of mass for mass; gravitation. Synonyms--Mass Attraction--Gravitation.

Molecular Affinity. The attraction of molecules for each other as seen in the formation of double salts, the combining of water of crystallization with a salt, and in other cases; a phase of affinity belonging to chemistry, although outside of true atomic attraction.

Molecular Attraction. The attraction of molecules; physical affinity. Cohesion, the attraction of similar molecules for each other, and adhesion, that of dissimilar molecules, are examples. This should be distinguished from molecular affinity, a phase of chemical force.

Molecular Bombardment. When a gas contained in a vessel is brought to a sufficient state of rarefaction the molecules cease to be subject to the laws of diffusion, but move back and forth in straight lines from side to side of the vessel. Their courses can be affected by electric discharge, which can cause them to all impinge upon one of the electrodes, the positive one, producing luminous effects. The path, if referred to the negative electrode, tends to be normal to its surface, so that the resultant path may be curved, as the stream of molecules go to the positive electrode. The fanciful name of molecular bombardment is given to the phenomenon, the luminous effect being attributed to the impinging of the molecules against the positive electrode as they are projected from the positive. The course of the molecules is comparable to the stream of carbon particles from the positive to the negative electrode in an arc lamp. (See Matter, Radiant.)

Molecular Chain. The theoretical rows of molecules supposed to extend from anode to cathode in an electrolytic cell (see Cell, Electric--Grothüss' Hypothesis) are called molecular chains.

381 STANDARD ELECTRICAL DICTIONARY.

Molecular Rigidity. The tendency of the molecules of a mass to retain their position in a mass in resistance to polarizing or depolarizing force, the first being the effect of a magnetic field. It is the theoretical cause of coercive force, q. v., and of residual magnetism. (See Magnetism, Residual.)

Molecule. The smallest particle of matter that can exist alone. It is made up of atoms, but an atom can never exist alone, but only, with one or two possible exceptions, combined with one or more other atoms as a molecule. The molecules under present conditions are not in constant contact with each other, but are perpetually vibrating through paths, in solids probably in defined paths, in liquids and gases in perpetually new paths. The molecules collide with each other and rebound. This motion is the kinetic motion termed heat. At the absolute zero--minus 273.72° C. (-460.7° F.) the molecules would be in contact and quiescent. In the gaseous state the molecules of most substances occupy the same volume; those of a few elements occupy one-half and of others twice the normal volume. The mean free path of the molecule of hydrogen is about 1/20,000 mm. (1/508,000 inch) (Maxwell) or twice this length (Crookes), the collisions in hydrogen are about 17,750 millions per second; the diameter is about 8/10,000,000 mm. (8/254,000,000 inch) ; A particle of matter 1/4,000 mm. (1/102,000 inch) contains, it is supposed, about 40,000 molecules. The results of different authorities vary so widely as to deprive the subject of much of its interest. A Sprengel pump, such as used for exhausting Geissler tubes, or incandescent lamp bulbs, may leave only one hundred-millionth (1/100,000,000,) of an atmosphere present, giving the molecules a capability of an average free path of vibration 33 feet long.

Moment. When a force is applied so as to tend to produce rotation around a point, the product of the force by the shortest distance from the point of rotation to the extension of the line of the force. Such distance is the perpendicular to the extension of the line through the point of rotation.

Mordey Effect. A phenomenon observed in dynamo armatures. At full loads the hysteresis decreases. The effect is thus expressed by S. P. Thompson. "When an armature core is rotated in a strong magnetic field, the magnetization of the iron is being continually carried through a cycle, but in a manner quite different from that in which it is carried when the magnetizing force is periodically reversed, as in the core of a transformer. Mordey has found the losses by hysteresis to be somewhat smaller in the former case than in the latter."

Morse Receiver. The receiving instrument formerly universally used in the Morse system. It is now but little employed, the sounder having displaced it. Several types were invented.

It consists of machinery which carries a reel of paper ribbon arranged to be fed over a roller by clockwork. A pencil, inking roller, or embossing stylus (for the latter the roller must have a groove) is carried by an arm with restricted range of vibration just over the paper and roller. The armature of an electro-magnet is attached to the arm. When the magnet is excited the armature is attracted and the marking device is pressed on the paper. If the clockwork is in operation the marker will make a line as long as the armature is attracted. When released no mark will be produced. In this way the dots and dashes of the Morse code are made on a ribbon of paper.

As an inking arrangement a small roller is carried by the end of the vibrating arm. The embosser, or dry point stylus, was very extensively used. The clockwork was generally driven by descending weights.

Synonym--Morse Recorder.

382 STANDARD ELECTRICAL DICTIONARY.

Mortar, Electric. An electric toy which may have various modifications. In the cut a wooden mortar with recess to receive a ball is shown. Two wires enter the base but do not touch. On placing the ball in position and passing a spark from a Leyden jar across the interval between the wires, the heat and disturbance are enough to project the ball. Gunpowder may be used, the discharge being passed through a wet string to prolong the spark.

Fig. 244. ELECTRIC MORTAR.

Motor, Compound or Compound Wound. A motor which has two windings on the field magnets, one in parallel with that on the armature, the other in series therewith, exactly as in a compound dynamo. (See Dynamo, Compound.)

Motor, Differential. A differentially wound motor; with a compound wound field, whose series coil and shunt coil are wound in opposition to each other. It is virtually a compound wound dynamo. (See Dynamo, Compound Wound.)

Motor, Electric. A machine or apparatus for converting electric energy into mechanical kinetic energy. The electric energy is generally of the dynamic or current type, that is to say, of comparatively low potential and continuous or virtually continuous flow. Some electrostatic motors have, however, been made, and an influence machine can often be operated as a static motor.

Electric motors of the current type may be divided into two classes--direct current and alternating current motors.

Direct current motors are generally based on the same lines of construction as dynamos. One of the great discoveries in modern electricity was that if a current is passed through a dynamo, the armature will rotate. This fact constitutes the principle of the reversibility of the dynamo.

383 STANDARD ELECTRICAL DICTIONARY.

Motors built on the dynamo model may be series wound, shunt wound, or compound wound, or of the magneto type, in the latter case having a fixed field irrespective of any current sent through them. The field may be produced by an electro-magnet separately excited and unaffected by the current sent through the motor.

A current passed through a magneto or motor with separately excited field will turn it in the direction opposite to that required to produce the same current from it were it worked as a generator.

A current passed through a series wound motor acts exactly as above.

Both these facts follow from Lenz's law, q. v.

A current passed through a shunt wound motor acts oppositely to the above. The direction of rotation is the same as that required to produce a current of the same direction. This is because the field being in parallel with the armature the motor current goes through the magnet coils in the direction the reverse of that of the current produced in the armature when it is used as a dynamo. Hence this also carries out Lenz's law.

The compound wound motor acts one way or the other according as its shunt or series winding preponderates. The two may exactly balance each other, when there will be no motion at all. The series connections of a compound wound dynamo should therefore be reversed, making both series and shunt work in unison, if the dynamo is to be used as a motor.

The general principles of the electric motor of the dynamo, or continuous rotation type, can only be outlined here. The current passing through the field magnets polarizes them and creates a field. Entering the armature by the brushes and commutators it polarizes its core, but in such a way that the north pole is away from the south pole of the field magnet, and the same for the south pole. Hence the armature rotates. As it does this the brushes connect with other commutator sections, and the poles of the armature are shifted back. This action continues indefinitely.

Another class of motors is of the reciprocating type. These are now very little used. (See Motor, Reciprocating.)

One valuable feature of continuous rotation electric motors is the fact that they absorb energy, to a great extent proportional in amount to the work they have to do. The rotation of the armature in the field of the motor involves the cutting of lines of force by its coils. This generates an electro-motive force contrary in direction to that producing the actuating current. The more rapid the rotation the greater is this counter-electro-motive force. The motor armature naturally revolves faster with diminished resistance to the motion of the armature. This increases the counter-electromotive force, so that less energy is absorbed. When the motor is called on to do work, the armature rotates more slowly, and the counter-electro-motive force diminishes, so that the machine absorbs more energy. (See Jacobi's Law.)

384 STANDARD ELECTRICAL DICTIONARY.

Motor Electro-motive Force. The counter-electro-motive force of a motor. (F. J. Sprague.)

A motor rotates in virtue of the pull of the field magnet upon the poles of the core of its armature. In responding to this pull the windings of the armature cuts lines of force and hence generates a counter-electro-motive force, for which the above term was suggested.

Motor-Generator. A combined motor and generator used to lower the potential difference in a portion of a circuit, e. g., that part within a building.

A motor-generator is a dynamo whose armature carries two commutators, with two separate windings, one of fine wire of many turns, the other of coarse wire of few turns. If the potential of the system is to be lowered, the main current is passed through the fine winding. This causes the armature to turn motor-fashion, and a potential difference is generated by the rotation of the large coils in the field. This potential difference is comparatively low and by properly proportioning the windings may be lowered to as great a degree as required.

The same apparatus may be inverted so as to raise potential difference. It acts for continuous current systems as the induction coil transformer does for alternating current systems.

Synonym--Continuous Current Transformer.

Motor, Multiphase. A motor driven by multiphase currents. It is arranged in general terms for distribution of the multi phase currents in coils symmetrically arranged around the circle of the field. These coils are wound on cores of soft iron. A rotating field is thus produced, and a permanent magnet or a polarized armature pivoted in such a field will rotate with the field, its poles following the poles of the rotatory field.

The cut, Fig. 245, illustrates the principles of action of a four phase current motor, connected to a four phase current dynamo or generator. The generator is shown on the left hand of the cut and the motor on the right hand. In the generator the armature N S is supposed to be turned by power in the direction shown by the arrow. Each one of the pair of coils is wound in the reverse sense of the one opposite to it, and the two are connected in series with each other, and with a corresponding pair in the motor. The connection can be readily traced by the letters A A', a a' for one set of coils and B B' b b' for the other set.

385 STANDARD ELECTRICAL DICTIONARY.

For each rotation of the armature two currents, each in opposite direction, are produced in A A', and the same is the case for B B'. These currents which have an absolutely constant relation of phase, and which it will be seen alternate four times for each rotation of the armature, regulate the polarity of the field of the motor. The resultant of their action is to keep the poles of the field magnet of the motor constantly traveling around its circle. Hence the armature N S of the motor, seen on the right hand of the cut, tends to travel around also its north and south poles, following the south and north poles of the rotatory field respectively.

Fig. 245. FOUR-PHASE CURRENT GENERATOR AND MOTOR.

It is not essential that the armature should be a magnet or polarized. Any mass of soft iron will by induction be polarized and will be rotated, although not necessarily synchronously, with the rotatory field. Any mass of copper, such as a disc or cylinder, will have Foucault currents induced in it and will also rotate. The only components of such currents which are useful in driving the motor are those which are at right angles to the lines of force and to the direction of motion. A very good type of armature based on these considerations is a core of soft iron wound with insulated copper wire in one or more closed coils; and so wound as to develop the currents of proper direction.

Such an armature is used in the Tesla alternating current motor. An efficiency of 85 per cent. has been attained with some of the Tesla motors.

Motor, Prime. A machine used for producing mechanical motion against resistance. It may operate by converting heat or any other form of kinetic or potential energy into mechanical energy of the moving type. A steam-engine and a water-wheel are examples of prime motors.

Motor, Reciprocating. The early type of motor depending upon reciprocating motion, such as the motion of a coil in a solenoid. These were based upon the lines of a steam engine, and have been abandoned except for special purposes where reciprocating motion is especially required, as in the case of rock drills.

386 STANDARD ELECTRICAL DICTIONARY.

Fig. 246. RICORDON'S RECIPROCATING MOTOR.

In the cut, B is an electro-magnet; A is an armature; E a pole piece. The current enters by the springs, b b, and by commutation is supplied and cut off alternately, thus maintaining a reciprocating movement of the armature and rotation of the fly-wheel.

Synonym--Pulsating Motor.

Motor, Series. A motor whose winding on the armature is in series with the winding on the field. It is similar to a series dynamo. (See Dynamo, Series.)

Motor, Shunt. A motor whose winding on the armature is in parallel with the winding on the field magnets. It is similar to a shunt wound dynamo. (See Dynamo, Shunt.)

Fig. 247. MULTIPLE ARC CONNECTION.

Multiple. A term expressing connection of electric apparatus such as battery couples, or lamps in parallel with each other. In the ordinary incandescent lamp circuits the lamps are connected in multiple.

Synonym--Multiple Arc.

387 STANDARD ELECTRICAL DICTIONARY.

Multiple Arc Box. A resistance box arranged so that the coils may be plugged in multiple instead of in series. Such can be used as a rheostat, as the resistance can be very gradually changed by putting the coils one by one into parallel with each other. Thus by adding in parallel with a 10 ohm coil a 10,000 ohm coil the resistance is decreased to 9.999001 ohms, and thus the resistance can be very slowly changed without sudden stops or abrupt changes.

[Transcriber's note: The correct value is 9.99001]

Multiple Series. Arrangements of electric apparatus in a circuit in a number of series, which minor series are then arranged in parallel. The term may be used as a noun, as "arranged in multiple-series," or as an adjective, as "a multiple-series circuit."

Fig. 248. MULTIPLE SERIES CONNECTION.

Multiple Switch Board. A switch board on whose face connecting spring jacks or other devices are repeated for the same circuits, so that different operators have each the entire set of connections repeated on the section of the board immediately in front of and within their reach. This multiplication of the same set of connections, giving one complete set to each operator, gives the title "multiple" to the type of switch board in question. The typical multiple switch board used in telephone exchanges is the best example of this construction. The calling annunciators of the subscribers are distributed along the bottom of the board extending its full length. To each operator a given number is assigned, all within reach of the right or left hand. This gives five or six feet length of board to each, and an operator only responds to those subscribers within his range. But anyone of his subscribers may want to connect with any of the others in the entire central station. Accordingly in front of each operator spring jacks are arranged, one for each of the entire set of subscribers connected in that office. The operator connects as required any of the calling subscribers, who are comparatively few, to any one of the large number served by the central station. Thus the entire set of subscribers' spring jacks are multiplied over and over again so as to give one set to each operator.

388 STANDARD ELECTRICAL DICTIONARY.

Multiple Wire Method for Working Electro-magnets. A method for suppressing sparking in working electro-magnets intermittently. The magnet core is wound with a number (from four to twenty) of separate layers of fine wire. A separate wire is taken for each layer and all are wound in the same direction, from one end to the other of the space or bobbin without returning. The ends are then joined so as to bring all the wires in parallel. The effect of this is that as the coils vary in diameter the time constants of each is different from that of the others, the coefficient of self-induction being less, and the resistance being greater for the coils farthest from the central axis. Thus the extra currents run differently in the different coils, and only a comparatively small spark can be produced owing to the division of forces thus brought about.

Fig. 249. DIAGRAM ILLUSTRATING MULTIPLE WIRE WORKING.

Multiplex Telegraphy. Any system of telegraphy transmitting more than four messages simultaneously over a single wire. Properly it should apply to all transmitting more than one, but conventionally has the above restricted meaning, distinguishing it from duplex and quadruplex telegraphy.

Multiplying Power of a Shunt. When a resistance is placed in parallel with a galvanometer on a circuit the following relation obtains. Let s and g equal the resistances of the shunt and galvanometer respectively, S and G the currents in amperes passing through them, V the potential difference between their common terminals, and A the whole current in amperes. Then we have A = ( (s + g ) / s ) * G and ( (s + g ) / s ) is termed the multiplying power of the shunt, as it is the factor by which the current passing through the galvanometer must be multiplied by to produce the total current.

Muscular Pile. A species of voltaic battery, often termed Matteueci's pile, made up of alternate pieces of muscle cut longitudinally and transversely respectively. The different pieces represent the elements of a battery, and their difference of potential is naturally possessed by the pieces.

Myria. A prefix; one million times. Thus myriavolt means one million volts.

[Transcriber's note: Contemporary usage is mega, as in megavolt.]

389 STANDARD ELECTRICAL DICTIONARY.

N. (a) Symbol for north pole or north-seeking pole of a magnet.

(b) Symbol for the number of lines of force in a magnetic circuit.

Nairne's Electrical Machine. The cylinder electrical machine, q.v.

Napierian Logarithms. A series of logarithms the base of whose system is 2.72818. They are also called hyperbolic logarithms.

Nascent State. An element just separating from a combination possesses at that time higher affinities than after separation, and can effect more powerful chemical changes.

It is sometimes attributed to a differential time of existence in the atomic modification, before the freed atoms have united to form molecules.

Natural Currents. A term for earth currents. (See Current, Earth.)

Needle. (a) A term applied to a bar magnet poised horizontally upon a vertical point, or suspended in a horizontal position by a filament. Thus the magnet in a mariner's compass, which may be a substantial bar magnet, is called a magnetic needle.

(b) An indicator in general shape like the hand of a clock. (Sec Annunciator, Needle- Telegraph, Needle.)

Needle of Oscillation. The magnetic needle poised horizontally, and used for measuring the intensity of the earth's magnetic field, or of an artificial magnetic field, by the method of oscillations. The intensities of the field is inversely as the square of the number of oscillations performed in a given time.

Needle, Telegraphic. The index in needle telegraphy (see Telegraph, Needle), whose motions indicate the characters it is desired to transmit.

Negative Charge. One of the two kinds of electric charges. The other is the positive.

By the double fluid hypothesis this is assumed to be a charge of a particular kind of electricity--negative electricity.

By the single fluid hypothesis it is supposed to be caused by the absence of part of the normal electricity of a surface. The reverse is held by some theorists.

The subject is so purely theoretical that neither of the two hypotheses is accepted as final.

[Transcriber's note: Current is a wire is the motion of negative electrons. Current in a electrolyte is the motion of positive ions and negative ions. Current in a plasma is the motion of electrons and positive ions.]

390 STANDARD ELECTRICAL DICTIONARY.

Negative Electricity. The kind of electricity with which a piece of amber is charged by friction with flannel; resinous electricity. (See Electrostatic Series.)

In a galvanic battery the surface of the zinc plate is charged with negative electricity.

According to the single fluid theory negative electrification consists in a deficiency of electricity.

[Transcriber's note: Negative electrification is an excess of electrons.]

Negative Element. In a voltaic cell the plate not dissolved by the solution; the one which is positively charged; the copper, platinum, or carbon plate in the usual type of battery.

The current is assumed to flow from negative element to positive element (the zinc plate) through the wire or other external conductor.

Nerve Currents. Currents of electricity obtained from nerves. They are much more feeble than those obtained from muscle, but are produced in the same general ways.

Network. Conductors in parallel and crossing each other, with connections at the junctions.

The term is sometimes so loosely applied as to include parallel conductors.

Neutral Line of Commutator. The diameter of a commutator which connects its Neutral Points, q. v.; sometimes termed the diameter of commutation; the diameter approximately at right angles with the lines of force. The commutator brushes are applied at the extremities of this diameter.

Neutral Point of a Commutator. The points of a commutator at which no lines of force are cut; the points at the extremities of a diameter which, except for the lag, would be at right angles to the lines of force; the points at which the brushes touch the commutator.

Neutral Point, Thermo-electric. A temperature marking a point of no thermo-electric difference of potential. If the junctions of a thermo-electric couple are at temperatures, one a little over and the other an equal amount under the neutral point, no current will be developed. At the neutral point the thermo-electric polarities are reversed. Differences of temperature above it give currents of reverse direction to those given by corresponding differences below it. For an iron-copper couple the neutral point is 274.5° C. (526° F.)

Synonym--Neutral Temperature.

Neutral Relay Armature. An unpolarizable armature for use with a relay; an armature of soft iron or iron wire; as distinguished from a polarized armature.

391 STANDARD ELECTRICAL DICTIONARY.

Neutral Wire. The central wire in the three wire system, q. v., of electric distribution; the wire connected to a point between the two dynamos, or otherwise to the central point of the current generator.

Fig. 250. DIAGRAM OF THREE WIRE SYSTEM SHOWING NEUTRAL WIRE.

Neutral Wire Ampere Meter. An ampere meter connected in the circuit of the neutral wire to determine the current passing through it. Such determination is for the purpose of ascertaining how much more work is being done by one of the lateral leads than by the other.

Synonym--Balance Ampere Meter.

N. H. P. Symbol or contraction for "nominal horse power." This is a basis for rating the size of an engine.

Nickel. A metal; one of the elements; atomic weight, 58.8 ; equivalent, 29.4; valency, 2; specific gravity, 8.8. It is a conductor of electricity. Relative resistance, annealed (Silver = 1), 8.285 Specific Resistance, 12.47 microhms. Resistance of a wire (a) 1 foot long, weighing 1 grain, 15.206 ohms. (b) 1 foot long, 1/1000 inch thick, 74.963 " (c) 1 meter long, weighing 1 gram, 1.060 " (d) 1 meter long, 1 millimeter thick, .1587 " Resistance of a 1-inch cube, 4.907 microhms. Electro-chemical equivalent, (Hydrogen = .0105) .3087 mgs.

It is strongly paramagnetic, but loses this quality at 350º C. (662º F.)

It is important as a constituent of German silver, an alloy much used for resistance coils.

Nickel, Bath. A bath for the electro-deposition of nickel. A great many formulae have been given. Metallic nickel is dissolved in 1 vol. sulphuric acid mixed with 2 vols. water. Neutralize with ammonia, and add of ammonium sulphate one-half the weight of metallic nickel originally used; 135 parts of nickel will be enough for a bath of 10,000 parts.

392 STANDARD ELECTRICAL DICTIONARY.

Other formulae are as follows: Double nickel-ammonium sulphate, 4 parts. Ammonium carbonate, 3 " Water 100 " Nickel sulphate, nitrate or chloride, 1 " Sodium bisulphate, 1 " Water, 20 "

Nickel anodes are used in the bath to maintain the strength. Too much care cannot be exercised in the absolute cleanliness of the articles to be plated. A too alkaline bath gives a disagreeable yellow color to the deposit; too acid a bath gives badly adhering deposits.

Night Bell. An alarm bell in a telegraph office, which bell is connected at night to give a loud signal to attract the operator's attention. It is used in telephone exchanges and is connected so as to ring as long as a subscriber remains unanswered after calling.

Nobili's Rings. When a dilute solution of copper acetate is placed on a bright silver plate and a strip of zinc is touched to the silver beneath the copper, a series of rings of copper are formed by electrolysis around the zinc. These are Nobili's rings.

If for the copper acetate a solution of lead oxide in potassium hydrate solution is substituted, and if the polished plate which may be German silver is connected to the positive electrode of a battery, and a platinum wire connected to the negative pole is immersed in the liquid, it determines the formation of beautiful iridescent rings of lead binoxide. The platinum wire is sometimes sealed in glass so that only its point projects.

The colors are due to interference of light, the layers of lead oxide being extremely thin.

The lead binoxide is formed by secondary reaction. Metallic lead is first deposited on the negative pole. The oxygen which goes to the positive pole formed by the polished plate produces lead binoxide which is deposited there in rings. The reaction is comparable to that of a storage battery.

Synonyms--Metallochromes--Electric Rings.

Nodular Deposit. A deposit obtained in electroplating, characterized by irregular thickness; due to too low density of current.

Non-conductor. A material that does not conduct electricity except with great difficulty; a substance of very high resistance.

Synonym--Insulator--Dielectric.

North Pole. (a) The north-seeking pole of a magnet; the pole of a magnet which tends to point to the north, and whence lines of force are assumed to issue on their course to the other pole of the magnet.

(b) The North Pole of the earth. Treating the earth as a magnet, and accepting the above nomenclature the north pole should be termed the south pole. (See Austral Pole--Boreal Pole.)

393 STANDARD ELECTRICAL DICTIONARY.

North-seeking Pole. The pole of a magnet which tends to point to the north; the north pole of a magnet.

Null Method. Any method of obtaining measurements or comparisons, in which the measurement is correct when the deflection of the galvanometer or other indicator is zero, nought or null. The Wheatstone Bridge (see Bridge, Wheatstone) is an example of a null method.

Two obvious advantages attach to null methods in electric galvanometer work. One is that an uncalibrated galvanometer can be employed. The other is that a galvanometer of any high degree of sensitiveness can be employed, there being no restriction as to its fineness of winding or highness of resistance.

"Upper case Omega Graphic". (Greek capital" Omega") symbol for megohm. [Transcriber's note: Now used for ohms.]

"Lower case Omega Graphic". (Greek omega) symbol for ohm. [Transcriber's note: Now used for angular velocity, 2*PI*frequency.]

Occlusion. An absorption of gases by metals. Palladium will, if used as the hydrogen evolving electrode in decomposing water, absorb 980 times its volume of hydrogen, which is said to be occluded. The metal may also be heated in hydrogen and allowed to cool therein, when occlusion occurs. Platinum will occlude 4 times its volume of hydrogen; iron, 4.15 times its volume of carbon-monoxide; silver, 7 times its volume of oxygen. Metals with occluded gases may serve as elements in a galvanic couple. (See Gas Battery.) A metal expands in occluding a gas.

In the storage battery it is believed that occlusion plays a part, hydrogen and oxygen being respectively absorbed by the two sets of plates, and acting as they do in Groves' gas battery.

Oerstedt. Name proposed for the unit of current strength, but not adopted. The ampere is the accepted name.

394 STANDARD ELECTRICAL DICTIONARY.

Oerstedt's Discovery. Oerstedt discovered in 1820 that a magnetic needle tended to place itself at right angles to a current of electricity. This fundamental experiment is the basis of the galvanometer.

Fig. 251. OERSTEDT'S DISCOVERY.

Ohm. The practical unit of resistance; 1E9 C. G. S. electro-magnetic units. The legal ohm is the resistance of a mercury column 1 square millimeter in cross-sectional area and 106 centimeters in length. There has been considerable confusion, owing to inaccuracy in early determinations, in the valuation of the ohm. In this work the legal ohm is used. The different ohms will be found defined in their place. Resistance units of various names may also be consulted.

The following table gives the relative values of the different ohms.

Length of Mercury Board of Column in True B. A. Trade Legal Centimetre. Ohm. Ohm. Ohm. Ohm.

True Ohm, 106.24 1. 1.0128 .9994 1.0022 B. A. Ohm, 104.9 .9874 1. .9868 .9889 Board of Trade Ohm 106.3 1.00050 1.0133 1. 1.0028 Legal Ohm, 106.0 .9977 1.0112 .9971 1.

Ohmage. The Resistance of a circuit expressed in ohms.

Ohm, B. A. The British Association unit of resistance; the resistance of a column of mercury 1 square millimeter in cross sectional area and 104.9 centimeters long; the B. A. Unit of Resistance.

Ohm, Board of Trade. The approximate ohm as recommended by the British Board of Trade on the advice of a committee (Sir W. Thomson, Dr. J. Hopkinson, Lord Rayleigh and others). It is the resistance of a mercury column one square millimeter in section, and 106.3 centimeters long at 0º C. (32º F.)

Synonym--New Ohm.

395 STANDARD ELECTRICAL DICTIONARY.

Ohmic Resistance. True resistance as distinguished from spurious resistance, or counter-electro-motive force.

Ohm, Legal. The practical unit of resistance. The resistance of a column of mercury one square millimeter in cross-sectional area and 106 centimetres long at 0º C. (32º F.) The ohm used previously to 1884 is the B. A. Unit of Resistance, q. v.

One legal ohm = 1.0112 B. A. Units, and I B. A. Unit = 0.9889 legal ohm.

The resistance of a copper wire 1 foot long and 1/1000 inch in diameter is about 10 ohms. The resistance of 1 mile of iron wire 1/3 inch in diameter is about 10 ohms.

Synonym--Congress Ohm.

396 STANDARD ELECTRICAL DICTIONARY.

Fig. 252. THEORY OF OHMMETER.

Fig. 253. OHMMETER.

Ohmmeter. An instrument for measuring directly the resistance of a conductor or of any part of a circuit through which a strong current is passing. It is the invention of Prof. W. E. Ayrton.

It contains two fixed coils at right angles to each other acting on the same needle of soft iron. One coil is of thick wire and is placed in series with the resistance to be measured. The other is of very thin wire and is placed in parallel with the same resistance. One wire acts by the total current, the other by the potential difference between the ends of the resistance. The action on the soft iron needle is due to the ratio of potential difference to total currents, or to the resistance itself. By properly designing and proportioning the coils the angular deflections of the needle are made proportional to the resistance.

In use the thick wire may be kept permanently in circuit. On connecting the binding posts of the thin wire coil to any two parts of the circuit its resistance is at once given by the deflection of the needle.

When no current is passing the needle rests in any position. A current in the thick coil brings it to zero. A current simultaneously passing through the thin high resistance coil brings about the deflection.

The instrument is a commercial rather than a scientific one.

Ohm's Law. The fundamental law expressing the relations between current, electro-motive force and resistance in an active electric circuit. It may be expressed thus:

(a) The current strength is equal to the electro-motive force divided by the resistance.

(b) The electro-motive force is equal to the current strength multiplied by the resistance.

(c) The resistance is equal to the electro-motive force divided by the current strength. All these are different forms of the same statement. Algebraically the law is usually expressed thus, (a) C = E/R. It may also be expressed thus: (b) E = C*R and (c) R= E/C, in which R denotes resistance, C denotes current strength, and E denotes electro-motive force.

Ohm, True. The true ohm is the resistance of a column of mercury 1 square millimeter in cross-sectional area, and 106.24 centimeters long. (See Ohm.)

Synonym-Rayleigh Ohm.

Oil Insulation. Oil insulation has received several applications in electrical work. It has been proposed for use in underground conduits. These it was proposed to fill with oil after the insertion of the conductors, the latter properly wrapped with cotton or other covering. For induction coils it has been very successfully used. Its principal utility depends on the fact that it is liquid, so that if pierced by a spark it at once closes again. A solid insulator if pierced is permanently injured. It is also used in telegraph insulators (see Insulator, Liquid) to prevent surface leakage.

397 STANDARD ELECTRICAL DICTIONARY.

Olefiant Gas. A compound gas; C2H4; composed of carbon, 24; hydrogen, 4; molecular weight, 28; specific gravity, .981.

It is a dielectric of about the resistance of air. Its specific inductive capacity at atmospheric pressure is 1.000722 (Boltzman.)

Synonym--Ethene; heavy carburetted hydrogen.

[Transcriber's note: Also called ethylene. A primary use is polyethylene plastic.]

Open. adj. An electric circuit is said to be open when it is cut or broken so that no current can pass through it. The term may be recollected by thinking of a switch; when open no current can pass through it. The same adjective is applied to magnetic circuits, an air gap implying an open circuit.

Open Circuit Oscillation. An oscillation of current in open circuit so that a spark discharge accompanies it. It is produced by electric resonance in a simple circle or loop of wire with ends placed near together but not touching, if the circuit is of such size that its period of oscillation corresponds with that of the inducing discharge. (See Resonance, Electric.) Its period depends entirely on the self-induction of the circuit.

Ordinate. In a system of plane co-ordinates (see Co-ordinates), the distance of any point from the axis of abscissas measured parallel to the axis of ordinates.

Ordinates, Axis of. The vertical axis in a system of co-ordinates, q. v.

Synonym--Axis of Y.

Organ, Electric. An organ in which the air blast is admitted or excluded from the different pipes by electric mechanism.

The outlines of the system are a series of contacts worked by the keys and stops, which cause, when operated by the organist, a current to pass through electro-magnets, opening the valves of the different pipes. Thus the manual may be at any distance from the organ, and a number of organs may be worked upon the same manual. As many as five in a single cathedral are thus connected to a manual in the chancel.

Orientation of a Magnetic Needle. The acquirement by a magnetic needle of its position of rest, with its magnetic axis in the magnetic meridian.

Origin of Co-ordinates. In a system of linear co-ordinates the point of intersection of the axes; the point whose co-ordinates are both zero.

398 STANDARD ELECTRICAL DICTIONARY.

Oscillating Needle. A small light bar magnet suspended by a filament and employed in determining the intensity of a magnetic field by the oscillations it completes in a given time after a given disturbance.

Oscillations, Electric. In static electricity the sudden and very rapid alternations in the discharge of a static condenser. This discharge of the disruptive order seems a single one, but is really composed of a number of discharges alternating in direction and producing electro-magnetic ether waves, probably identical with light waves except that they are longer and far less rapid.

Oscillatory Electro-motive Force. Electro-motive force rapidly changing in sense or in direction, so that it presents an oscillatory character. The alternating current and the telephone current as used in practice are actuated by this type of electro-motive force.

Osmose, Electric. When two liquids are separated by a porous diaphragm, and a strong current of electricity is passed through from the liquid on one side, through the diaphragm, to the liquid on the other side, the liquid on the side towards which the current is passing rises in level. The process is termed electric osmose. When a liquid is forced through a diaphragm a current is produced; in other words electric osmose is reversible. The current thus produced is termed a diaphragm current.

Oscillation, Electric. The phase of discharge of a static condenser in one direction. It is usually followed by a discharge in the opposite direction constituting a second oscillation, and so on, so that a great number of exceedingly short oscillations are comprised. Thus, in the discharge of the Leyden jar a large number of oscillations of current back and forth are produced, the current alternating like the swings of a pendulum.

These oscillations are supposed to affect the ether, producing waves in it identical with light waves, except that we have not been able yet to produce them short enough to affect the visual organs. The waves thus produced can be reflected or refracted; some substances are transparent for them and others opaque. There is a possibility that man may yet succeed in producing electric oscillations of sufficient frequency to bring about the direct production of light.

Oscillatory Displacement. Hypothetical displacement currents of rapidly alternating direction produced in the oscillatory discharge of a Leyden jar or static condenser.

Oscillatory Induction. Induction produced by sympathetic action of an oscillatory discharge or by electric resonance. (See Oscillations, Electric--Resonance, Electric--Resonator, Electric.)

399 STANDARD ELECTRICAL DICTIONARY.

Outlet. The part of an electrolier or electric light fixture out of which the wires are led for attachment of an incandescent light socket.

Output. The rate of energy delivered or of work done by a machine. In the case of a current generator it is the volt-coulombs per given second, or better the volt-amperes delivered at its outer circuit terminals.

Output, Magnetic. The analogue in a magnetic circuit of the output of an electric circuit. It is the product of the magnetizing force by the induced magnetism.

Output, Unit of. As a unit of output of a dynamo Prof. Sylvanus P. Thompson has proposed 1,000 watts, or one kilowatt. This unit is now frequently used. To completely define the dynamo, however, the amperage or the voltage must also be given, as a 10 kilowatt--110 volt machine, or a 10 kilowatt--99 ampere machine.

[Transcriber's note: 10 kilowatt at 110 volts is 91 amperes.]

Over-Compounding. A proportioning of the series and shunt windings of a compound dynamo, so that the voltage of the terminals rises with the load or output enough to allow for the drop in mains, thus maintaining the potential for full load at distant points in a district. It is carried out by an increase of ampere-turns in the series winding.

Overload. In an electric motor a mechanical load put upon it so great as to prevent economical working. One effect of such a load is to make the armature run so slowly as to unduly reduce the counter-electro-motive force and hence to permit so much current to pass through the coils as to heat them, perhaps injuriously. In this case the production of heat implies the waste of energy.

Overtype Dynamo or Motor. A dynamo or motor whose armature is placed above or in the upper part of the field magnets, the yoke piece of the magnets being in or resting upon the base of the machine.

Ozone. An allotropic form of oxygen. It possesses much more energetic chemical properties than oxygen. It is supposed to contain three atoms of oxygen in its molecule, represented thus: O / \ O---O

It is produced by electric discharges and it is its peculiar odor which is noticed about an electric machine, and sometimes in a thunderstorm near the path of a lightning flash.

In the electrolysis of water some ozone may be produced, thus diminishing the volume of the oxygen or of the mixed gases given off. This is a source of inaccuracy in a gas voltameter.

400 STANDARD ELECTRICAL DICTIONARY.

Pacinotti's Inductor. The Pacinotti or Gramme Ring. (See Pacinotti's Ring.)

Pacinotti's Ring. A ring of iron wire wound with coils of insulated wire at right angles to its circular axis, and used as the armature of a dynamo or motor. A number of connections are taken from the coils to a central commutator.

Fig. 254. PACINOTTI'S MACHINE, WITH RING ARMATURE.

If such a ring with its coils is rotated in a field, current can be taken from points of the commutator on a line at right angles to the lines of force entering the ring.

The ring was discovered in 1862 by Pacinotti, and later was independently discovered by Gramme. It is often known as the Gramme ring.

Pacinotti Teeth. Projections on a cylindrical or drum armature, between which in the grooves formed thereby, the wire is wound. The teeth being of iron tend to diminish the reluctance or magnetic resistance of the interpolar space, or interval between the poles of the field magnet.

Synonym--Pacinotti Projections.

Paillard Alloys. Non-magnetic palladium alloys, invented by Paillard, of Switzerland, used in anti-magnetic watches. The following are given as the compositions of several such alloys:

I. II. Palladium, 60 to 75 parts 50 to 75 parts Copper, I5 to 25 " 20 to 30 " Iron. 1 to 5 " 5 to 20 "

401 STANDARD ELECTRICAL DICTIONARY.

The following are more complex: I. II. Palladium, 65 to 75 parts 45 to 50 parts Copper, 15 to 25 " 15 to 25 " Nickel, 1 to 5 " 2 to 5 " Silver, 3 to 10 " 20 to 25 " Gold, 1 to 2-1/2 " 2 to 5 " Platinum, 1/2 to 2 " 2 to 5 " Steel, 1 to 5 " 2 to 5 "

These alloys are used for balance springs, as well as for the balance wheels and escapement parts of watches. The elasticity of recently produced springs has been found to be very satisfactory.

Page Effect. The sounds produced by magnetizing and demagnetizing a bar of iron or steel; the magnetic tick. The sounds are strong enough to produce a telephonic effect. (See Magnetic Tick.)

Palladium. A metal of the platinum series. It has the highest power of occlusion, q.v., of all metals. It is the characteristic ingredient of non-magnetic watch alloys.

Palladium used as an electrode in the electrolysis of water will occlude 936 volumes of hydrogen, and the hydrogen-palladium alloy will exceed in size the original electrode.

Fig. 255. LUMINOUS PANE.

Pane, Luminous. A pane of glass, one side of which has pasted to it a long zigzag strip of tinfoil. A design is made by cutting through the strip. On discharging a Leyden jar or an electric machine through the strip sparks appear where the tinfoil is severed, thus producing the design in a luminous effect. Many variations can be employed in their construction.

402 STANDARD ELECTRICAL DICTIONARY.

Pantelegraphy. A system of telegraphy for transmitting designs, maps, drawing, and the like by telegraphy. (See Telegraphy, Facsimile.)

Paper Filaments. Filaments of carbon for incandescent lamps made from paper.

This is one of the earliest materials practically used. The paper is cut out of proper shape, and is carbonized in a close vessel, while embedded in powdered charcoal or some other form of carbon to absolutely cut off access of air. It is then placed in the lamp chamber and flashed or subjected to the regular treatment.

Parabola. A curve; one of the conic sections. It is approximately represented by a small arc of a circle, but if extended becomes rapidly deeper than a half circle.

If, from a point within called the focus, lines are drawn to the curve and then other lines are drawn from these points parallel to the axis, the angles of incidence will he equal to the angles of reflection as referred to tangents at the points where the lines touch the curve.

[Transcriber's note; The general equation of a parabola is A*x^2 + B*x*y + C*y^2 + D*x + E*y + F = 0 such that B^2 = 4*A*C, all of the coefficients are real, and A and C are not zero. A parabola positioned at the origin and symmetrical on the y axis is simplified to y = a*x^2 ]

Parabolic Reflector. A reflector for a light, a paraboloid or surface of revolution whose section is a parabola. A light placed at its focus has its rays reflected parallel to each other.

Examples of parabolic reflectors are seen in electric search lights and in locomotive head-lights. They are employed in electric search lights. The arc light must be of such construction as to maintain its ignited points always at the same point, the focus of the paraboloid.

Paraffine. v. To coat or saturate with paraffine wax. Paper may be paraffined by dipping in the wax, or by being sprinkled with fragments of wax, subsequently melted in with a hot iron or otherwise. The tops of battery carbons are often paraffined to prevent the acid from rising in the pores by capillary attraction and rusting the connections.

403 STANDARD ELECTRICAL DICTIONARY.

Paraffine Wax. A hydro-carbon composed principally of mixtures of the higher members of the paraffine series C n H2 n + 2. It is made from cannel coal, coal tar, or petroleum by distillation. It is an insulator. Its resistance at 46° C. (114.8° F.) per centimeter cube is 3.4E16 ohms, or about the highest resistance known.

Its specific inductive capacity (for milky wax) is 2.47 (Schiller). For clear wax it is given as follows by different authorities: 1.92 Ayrton. 1.96 Wüllner. 1.977 Gibson & Barclay. 2.32 Baltzmann.

It is extensively used in condensers and other electric apparatus as a dielectric and insulator.

Paragrêles. Protectors against hail; lightning rods used to guard fields against hail; of little or no real utility.

Parallax. The apparent change in position of an object when looked at from two points of view. By looking at an object a few feet distant first with one eye and then with the other, the shifting in apparent position is seen.

In reading the position of an indicator or needle over a scale parallax introduces an error unless the eye is held vertically over the needle. By making the dial of looking- glass and holding the eye so that the reflection of its pupil is bisected by the needle this verticality is ensured.

Parallel. (a) In the nomenclature of electric circuits two or more conductors leading from one point to another, are said to be in parallel.

(b) When two or more conductors connect two main leads of comparatively large size and low resistance they are said to be in parallel or in multiple arc. This order is easiest pictured as the rungs of a ladder in parallel connecting its two sides representing the main leads.

It may be used as a noun as "arranged in parallel," or as an adjective as "a parallel circuit," the opposite of series, q. v.

Paramagnetic. adj. Possessing paramagnetic properties; tending to occupy a position with the longer axis parallel to the lines of force of a magnetic field; having magnetism; attracted by a magnet.

"If a homogeneous isotropic substance is placed in a magnetic field it becomes magnetized at every point in the direction of the magnetic intensity at that point, and with an intensity of magnetization proportional to the magnetic intensity. When the positive direction of the induced magnetization is the same as that of the magnetic intensity the substance is called Magnetic or Paramagnetic; when it is opposite, the substance is called Diamagnetic." (Emtage.)

A paramagnetic substance has high permeability or multiplying power for lines of force, hence in a magnetic field a bar of iron, etc., is in unstable equilibrium unless its longer axis is parallel with the lines of force in order to reduce as much as possible the reluctance of the circuit.

404 STANDARD ELECTRICAL DICTIONARY.

Iron is the most paramagnetic of all substances. Other paramagnetic metals are: Nickel, cobalt, manganese, platinum, cerium, osmium, palladium. Diamagnetic metals are bismuth, antimony, zinc, tin, mercury, lead, silver, copper, gold, arsenic. Bismuth is the most diamagnetic of all metals.

Of gases oxygen is most paramagnetic. Becquerel calculated that a cubic yard of oxygen condensed would act on a magnetic needle as powerfully as 5.5 grains of metallic iron. Liquefied oxygen will adhere to the poles of a magnet.

Changes of temperature and of other conditions may affect a body's magnetism. Thus hot oxygen is diamagnetic, and a substance paramagnetic in a vacuum may be diamagnetic in air.

Of liquids, solutions of iron or cobalt are paramagnetic; water, blood, milk, alcohol, ether, oil of turpentine and most saline solutions are diamagnetic.

Paramagnetism. (a) The science or study of paramagnetic substances and phenomena.

(b) The magnetic property of a paramagnetic substance; that of being attracted by a magnet, and of arranging itself with its longer axis parallel with the lines of force of a magnetic field.

Parchmentizing. If cellulose is treated with a mixture of two parts of sulphuric acid and one part of water perfectly cold, it becomes like parchment. It should at once be washed with water, and then with ammonia and water. The Swan incandescent light fibres are made of parchmentized cotton thread, which is afterward carbonized.

Partial Earth. A fault in a conductor caused by imperfect connection with the earth, where insulation from the earth is desired.

Passive State. A state of a substance in virtue of which it is unattacked by a solvent which ordinarily would dissolve or attack it. Iron in strong nitric acid is unattacked or assumes the passive state. This particular case is supposed to be due to a coating of magnetic oxide, so that there would be properly speaking no question of a passive state, but only one of superficial protection.

The existence of a true passive state of any substance is very doubtful.

P. D. Abbreviation for potential difference or difference of potential, or for electro-motive force.

405 STANDARD ELECTRICAL DICTIONARY.

Peltier Effect. The thermal effect produced by the passage of a current through the junction of two unlike conductors. Such junction is generally the seat of thermo-electric effects, and a current is generally produced by heating such a junction. If an independent current is passed in the same direction as that of the thermoelectric current, it cools the junction, and warms it if passed in the other direction. In general terms, referring to thermo-electric couples, if passed through them it tends to cool the hot and heat the cool junction. The phenomenon does not occur in zinc-copper junctions.

Peltier's Cross. A bar of bismuth and a bar of antimony soldered centre to centre at right angles, being notched or halved there to receive or to set into each other. It is used to demonstrate the Peltier effect, q. v. To one pair of ends are connected the terminals of a battery circuit; to the other pair are connected the terminals of a galvanometer.

The galvanometer by its deflections in one and then in the other direction indicates that the junction is heated when the current passes from antimony to bismuth and vice versa. It thus illustrates the heating and cooling of a thermo-electric junction by a current of electricity. The current from the battery by the Peltier effect either heats or cools the junction, as the case may be. This heating or cooling them produces a thermo-electric current in the galvanometer circuit. The battery has no direct influence on the galvanometer.

Pendant Cord. A double conductor or pair of conductors, insulated from each other and covered with a worsted, silk, or cotton covering and used to suspend incandescent lamps and at the same time to conduct the current to them. It is also used for other similar service, such as acting as conductors for small motors. Often each conductor is composed of a number of thin wires laid together. This gives flexibility to the cord.

Synonym--Flexible Cord.

Pendulum, Electric. (a) A pendulum operated by the intermittent action of an electro-magnet, whose circuit is opened and closed by the pendulum itself. A point at the lower end of the pendulum swinging through a globule of mercury may close and open the circuit. Various other methods of accomplishing the same end are employed ..

(b) A pith ball suspended by a thread from an insulating stand. It is used to show the attraction exercised by a piece of sealing wax or other substance excited by rubbing.

406 STANDARD ELECTRICAL DICTIONARY.

Pen, Electric. A stylus for producing a series of perforations in paper, so that the paper may act as a stencil for the reproduction of a great number of copies of the original matter. Various kinds of electric pens have been invented. One kind, invented by Edison, consists of a handle carrying an electric motor actuating a needle, which is driven in and out of the other end of the handle with high rapidity. It is used by being held vertically on the paper with the needle end downward, and is moved so as to describe perforated letters or designs. The paper is then used as a stencil with an ink roller to reproduce the writing or design ad libitum. A simpler kind dispenses with the motor and depends on the perforations produced by the electric spark. As shown in the cut the stylus is one terminal of an induction coil circuit. The support on which the paper rests is the other terminal and must be a conductor. In use the induction coil is started, and the stylus is moved over the paper; a series of sparks pass through the paper from stylus to the supporting tablet, perforating the paper and producing a stencil to be used for reproduction.

Fig. 256. ELECTRIC PEN.

Pentane Standard, Harcourt's. A standard of illuminating power; in it the combustible substance is a gas made by mixing one cubic foot of air with three cubic inches of liquid pentane, measured at 60° F. or, if measured as gases, 20 volumes of air to 7 of pentane. It is burned at the rate of 0.5 cubic foot per hour from a cylindrical tube one inch in diameter, closed at the top by a disc 0.5 inch thick with a hole 0.25 inch in diameter, through which the gas issues. It gives a flame 2.5 inches high.

The pentane used is the distillate of petroleum which boils at 50° C. (122° F.) ; it has a specific gravity at 15° C. (60° F.) of from 0.628 to 0.631. It is almost pure pentane (C5H12).

As long as the rate of consumption is between 0.48 and 0.52 cubic foot per hour the flame gives practically the same light.

407 STANDARD ELECTRICAL DICTIONARY.

Perforator. An apparatus used in automatic high speed telegraphy for perforating strips of paper. These are then used by drawing between a roller and contact spring for making and breaking the telegraphic circuit for the production of a record, such as the Morse record, at the distant receiving station.

The perforated strip has different classes of holes punched in it to represent dots or dashes. It is fed by machinery very rapidly, so that the message is transmitted with the highest speed. Several operators may simultaneously prepare the paper strips, and thus in conjunction with its rapid feeding in the transmitter, far surpass the time of ordinary direct transmission.

Fig. 257. PERFORATOR FOR WHEATSTONE'S AUTOMATIC TELEGRAPH.

Perforators may be entirely mechanical but are sometimes pneumatic, compressed air being used to operate them. The holes they make are on different levels of the paper strip, as shown in the cut.

Period. The time required for the completion of one complete element of periodic motion. This may be a complete alternation (See Alternation, Complete) of an alternating current, or of an oscillatory discharge.

Periodicity. The rate of succession of alternations or of other fixed phases; the rate of recurrence of phenomena.

408 STANDARD ELECTRICAL DICTIONARY.

Permanency. In electric current conductors the property of possessing conductivity unaffected by lapse of time. Generally the permanency of conductors is very high. In some cases a slow annealing takes place which causes a gradual change with the lapse of time. Annealed German silver wire has been found to increase in conductivity at about .02 per cent. in a year. (Matthiessen.) Wire, whether annealed or not, is left in a strained condition after the drawing operations, and such a change is consonant with this fact. The figure only applies to the samples tested by Matthiessen.

Permanent State. In a telegraph line or other current conductor, the condition when a uniform current strength obtains over the whole line. When a current is started it advances through the line with a sort of wave front gradually increasing in strength. At the further end some time may elapse before it attains its full intensity. When its does the permanent state prevails. Until then the variable state, q. v., exists in the line.

Permeameter. An apparatus for determining the permeability of samples of iron. It consists of a large slotted block of iron. A coil is placed within the slot. A hole is drilled through one end, and a rod of the iron to be tested is passed through this hole and through the coil to the bottom of the slot. The lower end of the rod must be accurately faced off. The current is turned on, upon which the rod adheres to the bottom of the slot. The force required to detach it is determined with a spring balance. The permeation through its face is proportional to the square of the force required.

Fig. 258. PERMEAMETER.

Permeance. The multiplying or the conducting power for magnetic lines of force possessed by a given mass of material. It varies with the shape and size of the substance as well as with the inducing force. It is distinguished from permeability, as the latter is a specific quality proper to the material, and expressed as such; the permeance is the permeability as affected by size and shape of the object as well as by its material.

409 STANDARD ELECTRICAL DICTIONARY.

Pflüger's Law. A law of electro-therapeutics. It states that stimulation of a nerve is only produced by successive appearance of the kathelectrotonic state, and disappearance of the anelectrotonic state.

Phantom Wires. The extra transmission circuits obtained in multiplex telegraph systems. A single line arranged for four separate simultaneous transmissions by quadruplex apparatus is said to establish three phantom wires.

Phase. In wave motion, oscillating motion, simple harmonic motion, or similar periodic phenomena, the interval of time passed from the time the moving particle moved through the middle point of its course to the instant when the phase is to be stated.

Pherope. An apparatus for the electric transmission of pictures. (See Telephote.)

[Transcriber's note: Precursor of the contemporary Fax and scanner.]

Philosopher's Egg. An ellipsoidal vessel mounted with its long axis vertical and with two vertical electrodes, the upper one sliding, and arranged to be attached to an air pump. A discharge through it when the air is exhausted takes the general shape of an egg.

Phonautograph. An apparatus for registering the vibrations of a stylus, which is mounted on a diaphragm and is acted on by sound waves.

It is virtually a resonating chamber, over one of whose ends a parchment diaphragm is stretched. To the centre of the parchment a needle or stylus is attached. A cylinder covered with soot is rotated in contact with the point of the stylus. As the chamber is spoken into the diaphragm and stylus vibrate and the vibrations are marked on the cylinder. It is of some electric interest in connection with telephony.

Phone. Colloquial abbreviation for telephone.

Phonic Wheel. A form of small motor of very simple construction. It consists of a toothed wheel of soft iron. A bar electro-magnet is fixed with one pole facing the teeth of the wheel. By a tuning fork make and break a succession of impulses of rapid frequency and short duration are sent through the magnet. The teeth act as armatures and are successively attracted by the magnet. The regulated speed is one tooth for each impulse, but it may rotate at one-half the speed, giving two teeth for each impulse, or at certain other sub-multiples of its regular speed. It is the invention of Paul Lecour.

410 STANDARD ELECTRICAL DICTIONARY.

Phonograph. An apparatus for reproducing articulate speech. It is not electric, except as it may be driven by electricity.

It consists of a cylinder of wax-like material which is rotated and moved slowly, longitudinally, screw fashion, at an even speed. A glass diaphragm carrying a needle point is supported with the point barely touching the wax. If the diaphragm is agitated, as by being spoken against, the needle is driven back and forwards cutting a broken line or groove following the direction of the thread of a screw in the wax, the depth of which line or groove continually varies.

This imprints the message. If the needle is set back and the cylinder is rotated so as to carry the needle point over the line thus impressed, the varying depth throws the needle and diaphragm into motion and the sound is reproduced.

The cylinder is rotated often by an electric motor, with a centrifugal governor.

[Transcriber's note; Due to T. A. Edison, 1877, fifteen years before this book.]

Phonozenograph. An apparatus for indicating the direction of the point where a sound is produced. It operates by a microphone and telephone in conjunction with a Wheatstone bridge to determine the locality.

Phosphorescence. The emission of light rays by a substance not heated, but whose luminosity is due to the persistence of luminous vibration after light has fallen upon it.

A phosphorescent body, after exposure to light, is luminous itself. Phosphorescence may be induced by rubbing or friction, by heat, by molecular bombardment, as in Crookes' tubes, and by static discharge of electricity, as well as by simple exposure to light.

Another form of phosphorescence may be due to slow chemical combustion. This is the cause of the luminosity of phosphorous.

Phosphorous, Electrical Reduction of. Phosphorous is reduced from bone phosphate by the heat of the electric arc. The phosphate mixed with charcoal is exposed to the heat of the voltaic are, and reduction of the phosphorous with its volatilization at once ensues. The phosphorous as it volatilizes is condensed and collected.

Photo-electricity. The development of electrical properties by exposure to light. Crystals of fluor spar are electrified not only by heat (see Pyro-electricity) but also by exposure to sunlight or to the light of the voltaic arc.

[Transcribers note: Although first observed in 1839 by Becquerel, it was not explained until 1905 by Albert Einstein with the introduction of photons.]

Photo-electric Microscope. A projection, solar or magic-lantern microscope worked by the electric light.

Photo-electro-motive Force. Electro-motive force produced in a substance by the action of light.

411 STANDARD ELECTRICAL DICTIONARY.

Photometer. An apparatus for measuring the intensity of light emitted by a given lamp or other source of illuminating power. They may be classified into several types.

Calorimetric or Heat Photometers act by measuring relatively the heat produced by the ether waves (so-called radiant heat) emitted by the source. The accuracy of the instrument is increased by passing the rays through an alum solution. A thermopile, or an air thermometer, may be used to receive the rays.

Chemical Photometers. In these the light falls upon sensitized photographic paper. The depth of coloration is used as the index of illuminating power.

Direct Visual Photometers. These include Rumford's Shadow Photometer, Bunsen's Bar Photometer, and Wheatstone's Bead Photometer, in which the light is estimated by direct visual comparison of its effects.

Optical Photometers. These include Polarization Photometers, in which the light is polarized; Dispersion Photometers, in which a diverging lens is placed in the path of the rays of light so as to reduce the illuminating power in more rapid ratio than that of the square of the distance.

Selenium Photometers, in which the variations in resistance of selenium as light of varying intensity falls upon it is used as the indicator of the intensity of the light.

Jet Photometers, for gas only, in which the height of a flame under given conditions, or the conditions requisite to maintain a flame of given height, is used to indicate the illuminating power.

The subject of photometers has acquired more importance than ever in view of the extensive introduction of the electric light. (See Candle, Standard--Carcel--Violé's Standard--and Photometers of various kinds.)

Photometer, Actinic. A photometer whose registrations are produced by the action of the light being tested upon sensitized paper or plates, such as used in photography. Some efforts at self-registering photometers have been based on actinic registration of the height of a flame of the gas to be tested.

Photometer, Bar. A photometer in which the two lights to be compared are fixed at or opposite to the ends of a bar or scale of known length, generally 60 or 100 inches. The bar is divided by the rule of the inverse square of the distances, so that if a screen is placed on any part of the bar where it receives an equal amount of light from both sources, the figure on the bar will indicate the relative illuminating power of the larger lamp or light in terms of the smaller. The divisions of the bar are laid out on the principle that the illuminating power of the two sources of light will vary inversely with the square of their distance from the screen.

412 STANDARD ELECTRICAL DICTIONARY.

The screen used is sometimes the Bunsen disc. This is a disc of paper with a spot of paraffine wax in the centre melted thoroughly into the paper or with a ring of paraffine wax surrounding the untouched centre. When this disc is equally illuminated on both sides the spot is nearly invisible. Inequality of illumination brings it out more visibly. Sometimes a Leeson disc is used. This consists of three pieces of paper, two thin ones between which a thicker piece, out of which a star is cut, is laid. When equally illuminated on both sides the star appears equally bright on both sides.

The bar photometer is the standard form. A candle or pair of candles may be burned at one end and an incandescent lamp at the other, or a gas flame may first be rated by candles and used as a standard.

Synonyms--Bunsen's Photometer--Translucent Disc Photometer.

Fig. 259. BAR PHOTOMETER.

Photometer. Calorimetric. A photometer in which the radiant energy, so called radiant heat, is used as the measurer of the light.

In one type a differential air thermometer is used, one of whose bulbs is blackened. On exposing this bulb to a source of light it will become heated, and if lights of the same character are used the heating will be in proportion to their illuminating power quite closely. The heating is shown by the movements of the index. By careful calibration the instrument may be made quite reliable.

Photometer, Dispersion. A photometer in which the rays from one of the lights under comparison are made more divergent by a concave lens. In this way a strong light, such as all arc lamp can be photometered more readily than where only the natural divergence of the beam exists. The law of the variation of the intensity of light with the square of the distance is abrogated for a law of more rapid variation by the use of a concave lens.

The diagram, Fig. 260, illustrates the principle. E represents a powerful light, an arc light, to be tested. Its distance from the screen is e. Its light goes through the concave lens L and is dispersed as shown over an area A1, instead of the much smaller area A, which the same rays would otherwise cover. Calling l the distance of the lens from the screen, f its focus, and c the distance of the standard candle from the screen when the shadows are of equal intensity, we have the proportion.

Illuminating power of lamps: ditto of standard candle:: (l (e-l) + fe)2 : (c f)2

413 STANDARD ELECTRICAL DICTIONARY.

Fig. 260. DIAGRAM OF PRINCIPLE OF THE DISPERSION PHOTOMETER.

The cut, Fig. 261, gives a perspective view of Ayrton's Dispersion Photometer. C is the standard candle, L the concave lens, R the rod for producing the two shadows on the screen S.

Fig. 261. AYRTON'S DISPERSION PHOTOMETER.

The mirror M is fixed at an angle of 45° with the stem on which it rotates. The light of the arc lamp is received by the mirror and is reflected through the lens. The candle holder slides along a graduated bar C, and at D is an index plate to show the angle at which the spindle carrying the mirror is set.

414 STANDARD ELECTRICAL DICTIONARY.

Dr. J. Hopkinson in his dispersion photometer uses a double convex lens. This gives a focal image of the arc-lamp between the lens and screen, whence the rays diverge very rapidly, thus giving the desired dispersion effect.

It is principally for arc lamps that dispersion photometers are used.

Photometer, Shadow. A photometer in which the relative intensity of the two lights is estimated by the intensity or strength of shadows of the same object which they respectively cast.

Fig. 262. RUMFORD'S SHADOW PHOTOMETER.

Fig. 263. RUMFORD'S SHADOW PHOTOMETER ARRANGED FOR TESTING INCANDESCENT LAMPS.

415 STANDARD ELECTRICAL DICTIONARY.

A rod is supported in a vertical position. Back of it is a screen of white paper. The two lights to be compared are arranged in front of the rod and at a little distance from each other. They are shifted about until the two shadows appear of equal darkness. The relative intensity of the lights varies inversely with the square of their distances from the shadows cast respectively by them on the screen.

The cut, Fig. 262, shows the simplest type of the shadow photometer. In the cut, Fig. 263, a shadow photometer for testing incandescent lamps is shown. In it E is the lamp under trial supported by a clamp H. A is an ampere meter in circuit with the lamp, and V is a voltmeter. A candle C can be moved along a graduated scale G G. R is the vertical rod, and S is the screen on which the shadows fall.

Photophore. An instrument for medical examination of the cavities of the body. It includes an incandescent lamp mounted in a tube with a concave mirror and convex lens.

Photo-voltaic Effect. The change in resistance of some substances effected by light. Selenium, of all substances, is most susceptible to this effect. (See Selenium.)

Piano, Electric. A piano whose manual or key-board operates to close electric circuits, whereby electro-magnets are caused to operate to drive the hammers against the strings.

Pickle. An acid solution for cleaning metal surfaces before electro-plating, galvanizing or other deposition of metal upon them.

Picture, Electric. A picture produced by passing a strong discharge through a piece of gold leaf clamped or firmly pressed upon a sheet of paper. The gold leaf is cut out of the desired shape, or else a stencil of paper overlays it. The discharge dissipates the gold, and produces a purple colored reproduction of the design upon the paper. The design is due to the deposition of an exceedingly thin film of metallic gold.

Synonym--Electric Portrait.

Pile. A galvanic or voltaic battery. It is sometimes restricted to a number of voltaic couples connected. It should be only applied to batteries with superimposed plates and no containing vessel such as the Dry Pile, q. v., or Volta's Pile, q. v.

Pilot Transformer. In alternating current distribution a small transformer placed at any part of the system and connected to a voltmeter in the central station, to indicate the potential difference of the leads.

Pilot Wires. Wires brought from distant parts of electric light or power mains, and leading to voltmeters at the central station, so that the potential of distant parts of the system can be watched. The wires can be very small, as they have but little current to transmit.

416 STANDARD ELECTRICAL DICTIONARY.

Pistol, Electric. An experimental apparatus for exhibiting the power of electric incandescence or of the electric spark. A tube is mounted with a handle like a pistol. A plug is provided to screw in and out of its side. The plug carries two wires connected on its inner side by a fine platinum wire, or else disconnected but with their ends brought near together to act as terminals for the production of a spark. To use it the tube is filled with a mixture of air and gas, the latter either hydrogen, hydro-carbon or other combustible gas. The tube when full is corked. The wire is heated to incandescence by a current, or a spark is passed from a Leyden jar or other source of electrostatic excitation. The mixture, if properly proportioned, explodes and expels the cork violently.

Fig. 264. ELECTRIC PISTOL.

Pith. A light and soft cellular tissue forming the central core of exogenous trees and plants. In the older parts of the tree the woody tissue often encroaches in and partly obliterates it.

For electrical pith-balls, the pith of the elder, of corn, or, best of all, of sun-flower stems is used.

Pith-balls. Ball made of pith. They are used in the construction of electroscopes and for other experiments in static electricity.

They are cut out with a sharp knife and their shape may be improved by gentle rolling in the hand or between the fingers.

Pivot Suspension. Suspension poising or supporting of an object on a sharp pivot. This is used for the needle in the ordinary compass. A cavity or inverted cup, which may be made of agate, is attached to the middle of the needle which has a hole for its reception. The centre of gravity of the needle comes below the bottom of the cup.

Pivot suspension is not perfect, as it has considerable friction. There is no restitution force, as with torsion filaments.

417 STANDARD ELECTRICAL DICTIONARY.

Plant. The apparatus for commercial manufacturing or technical works. An electric lighting plant includes the boilers, engines and dynamos for producing the current, and the electric mains and subsidiary apparatus.

Plant Electricity. Electricity manifested by plant life. By means of a galvanometer potential differences are found to exist in different parts of trees or fruits. The roots and interior portions are negative, and the flowers, smaller branches and fruit are positive.

In some cases a contraction of the tissue of plants can be produced by an electric current. The sensitive plant and others exhibit this phenomenon, exactly analogous to the action of muscular tissue.

Plate, Arrester. In a lightning arrester the plate connected to the circuit. Sometimes both plates are designated arrester plates.

Plate Condenser. A static condenser having a flat plate of glass for dielectric. (See Epinus' Condenser.)

Plate Electrical Machine. A frictional electric machine, in which a circular plate of glass is excited by friction with the cushions. It is the most recent type of frictional machine and has superseded the old cylinder machines. In its turn it is superseded by influence machines, really plate machines, but not so termed in practice.

Plate, Ground. In a lightning arrester, the plate connected to the earth.

Plate, Negative. In a voltaic battery, either primary or secondary, the plate which is unattacked by the oxygen or negative radical or element of the fluid. It corresponds to the carbon plate in the ordinary voltaic battery, and is the one charged with positive electricity.

Plate, Positive. In a voltaic battery, either primary or secondary, the plate which is dissolved or attacked by the oxygen or negative radical or element of the fluid. It is the plate corresponding to the zinc plate in the ordinary voltaic battery, and is the one charged with negative electricity.

Plating Balance. A balance or scales to which articles in an electroplater's bath are suspended. A weight exceeding by a known amount that of the article as immersed overbalances the article. When the plating is being deposited as soon as it exceeds the excess of weight of the counterpoise the balance tips, the article descends a little, the electric circuit is broken and the plating ceases. Thus the plating is automatically stopped when a predetermined amount of metal is deposited.

418 STANDARD ELECTRICAL DICTIONARY.

Plating Bath. A vessel of solution for the deposition of metal by electrolysis as used in electro-plating.

Plating, Electro-. The deposition of metal by electrolysis so as to coat the conducting surface of objects therewith. The full details of the many processes are very lengthy and cannot be given here.

The general principle includes a battery or source of electric current. The object to be plated is connected to the negative terminal and is immersed in the solution. Thus with a battery the object is in electrical connection with the zinc plate. To the other terminal a metallic plate is connected. The object and the plate termed the anode being introduced into a suitable bath, the metal whose solution is in the bath is deposited upon the surface of the object.

The bath is a solution of the metal in some form that will lend itself to the electrolytic action. The anode is often a plate of the metal of the bath, so that it dissolves as fast as metal is deposited on the object, thus keeping up the strength of the solution.

The objects to be plated must be scrupulously clean, and great care must be taken to keep the bath uncontaminated.

When the object has a non-conducting surface, it is made conducting by being brushed over with plumbago q.v. In addition iron dust is sometimes dusted over it. This acts by precipitating the metal of the bath directly and thus giving a conducting basis for the metal to deposit on. To avoid getting iron in a bath the object may be dipped in copper sulphate solution. This precipitates copper in place of the iron and leaves the article in good shape for silver or other plating.

Electro-plating, if made thick enough, gives a reverse of the article when separated therefrom. A direct copy can be got by a second plating, on the first plating after separation, or a wax impression can be employed.

Under the different metals, formulae for the baths will be found. (See also Quicking-- Steeling--Plating Balance.)

Platinoid. An alloy of copper, nickel, zinc in the proportions of German silver with 1 or 2 per cent of tungsten. It is used for resistances. It has a specific resistance (or resistance per centimeter cube) of about 34 microhms. Its percentage variation in resistance per degree C. (1.8° F.) is only about .021 per cent., or less than half that of German silver. This is its most valuable feature.

419 STANDARD ELECTRICAL DICTIONARY.

Platinum. A metal; one of the elements; symbol, Pt; atomic weight, 197.4; equivalent, 49.35; valency, 4; specific gravity, 21.5. It is a conductor of electricity. The following data refer to the annealed metal at 0° C. (32° F.) Relative Resistance (Silver annealed = 1), 6.022 Specific Resistance, 9.057 microhms. Resistance of a wire, (a) 1 foot long, weighing 1 grain, 2.779 ohms. (b) 1 foot long, 1/1000 inch thick, 54.49 " (c) 1 meter long, weighing 1 gram, 1.938 " (d) 1 meter long, 1 millimeter thick, .1153 " Resistance of a 1 inch cube, 3.565 Electro-chemical equivalent (Hydrogen = .0105), 0.5181.

The coefficient of expansion by heat is almost the same as that of glass. It can be passed through holes in glass and the latter can be melted about it so as to hermetically seal its place of passage through the glass. It is used in incandescent lamps for leading-in wires and other similar uses.

Platinum Black. Finely divided platinum. It is made by boiling a solution of platinic chloride with excess of sodium carbonate and a quantity of sugar, until the precipitate is perfectly black and the supernatant liquid is colorless. It seems to possess a great power of occluding oxygen gas. When heated to redness it becomes spongy platinum. The negative plates of a Smee battery are coated with platinum black.

Platinum-silver Alloy. An alloy of 1 part platinum and 2 parts silver, used for resistance coils.

Relative Resistance (silver annealed = 1 ), 16.21 microhms. Specific Resistance at 0°C. (32° F.), 24.39 Resistance of a wire, (a) 1 foot long, weighing 1 grain, 4.197 ohms. (b) 1 foot long, 1/1000 inch diameter, 146.70 " (c) 1 meter long weighing 1 gram, 2.924 " (d) 1 meter long, 1 millimeter diameter, 0.3106 " Resistance of a 1 inch cube, 9.603 microhms. Percentage Variation per degree C. (1.8° F.) at about 20° C. (68° F.), 0.031 per cent.

Synonym--Platinum Alloy.

Platinum Sponge. Finely divided platinum obtained by igniting platinum black, q.v., and also by igniting salts of platinum. It has considerable power of condensing or occluding oxygen. It will, if in good condition, set fire to a jet of hydrogen impinging upon it.

Plow. Contact arms projecting downwards from the motors, trucks, or bodies of electric street cars, which enter the underground conduit through the slot and carry contact pieces or brushes, to take the current for driving the motors from the leads within the conduit.

420 STANDARD ELECTRICAL DICTIONARY.

Plücker Tubes. A special form of Geissler tube designed for the production of stratification and for observing the effects produced in the space surrounding the negative electrode.

Plug. (a) A piece of metal with a handle and a somewhat tapered end, used to make connections by insertions between two plates or blocks of metal slightly separated and with grooves to receive it.

(b) A plug or wedge with two metallic faces, insulated from each other with a separate wire connected to each one. It is used in spring-jacks q. v., to introduce a loop in a circuit.

Synonym--Wedge.

Plug. v. To connect by inserting a plug, as in a resistance box.

Fig. 265. PLUGS FOR RESISTANCE COIL BOX.

Fig. 266. PLUG SWITCH.

Plug, Double. A spring-jack plug or wedge with two pairs of insulated faces, one behind the other, so as to simultaneously introduce two loops into a circuit.

Plug, Grid. A piece or mass of lead oxide, inserted into the holes in the lead plates of storage batteries. The holes are often dovetailed or of uneven section to better retain the plugs.

Plug Infinity. In a box-bridge or resistance box, a plug whose removal from between two disconnected discs opens the circuit. All the other discs are connected by resistance coils of various resistance.

Plug Switch. A switch composed of two contact blocks, not touching each other and brought into electrical connection by the insertion of a metallic plug. The latter is usually provided with an insulating handle, and a seat is reamed out for it in the two faces of the contact blocks.

421 STANDARD ELECTRICAL DICTIONARY.

Plumbago. Soft lustrous graphite, a native form of carbon; sometimes chemically purified. It is used in electro-plating to give a conducting surface to non-conducting objects, such as wax moulds. The surface, after coating with plumbago, is sometimes dusted over with iron dust, which precipitates the metal of the bath and starts the plating. It is sometimes plated with copper, silver or gold, and is then termed coppered, silvered, or gilt plumbago. It is gilded by moistening with etherial solution of gold chloride and exposing to the air, and drying and igniting.

Plunger. A movable core which is used in connection with a so-called solenoid coil, to be drawn in when the coil is excited. (See Coil and Plunger.)

Fig. 267 COIL AND PLUNGER WITH SCALES TO SHOW ATTRACTION.

P. O. Abbreviation for Post Office, q.v.

Poggendorf's Solution. An acid depolarizing and exciting fluid for zinc-carbon batteries. The following is its formula: Water, 100 parts; potassium bichromate, 12 parts; concentrated sulphuric acid, 25 parts. All parts by weight. Use cold.

Point, Neutral. (a) On a commutator of a dynamo the points at the ends of the diameter of commutation, or where the brushes rest upon the surface of the commutator, are termed neutral points. At these points there is no generation of potential, they marking the union of currents of opposite direction flowing from the two sides of the armature into the brushes.

(b) In electro-therapeutics, a place in the intra-polar region of a nerve so situated with reference to the kathode and electrode as applied in treatment, that its condition is unaffected.

Synonym--Indifferent Point.

(c) In a magnet the point of no attraction, situated between the two poles, at about an equal distance from each, so as to mark the centre of a magnet of even distribution of polarity.

(d) In thermo-electricity the point of temperature where the thermo-electric powers of two metals are zero; in a diagram the point where the lines representing their thermo-electric relations cross each other; if the metals are arranged in a thermo-electric couple, one end at a temperature a given amount above, the other at a temperature the same amount below the neutral point, no current or potential difference will be produced.

422 STANDARD ELECTRICAL DICTIONARY.

Point, Null. A nodal point in electrical resonators; a point where in a system of waves or oscillations, there is rest, the zero of motion being the resultant of oppositely directed and equal forces. In electrical resonators it is to be sought for in a point symmetrically situated, with reference to the spark gap, or in a pair of points, which pair is symmetrically placed.

The null point in resonators is found by connecting a lead from one of the secondary terminals of an induction coil to different parts of the resonator. The null point is one where the connection does not give rise to any sparks between the micrometer knobs or spark gap, or where the sparks are of diminished size.

The whole is exactly comparable to loops and nodes in a vibrating string or in a Chladni plate as described in treatises on sound and acoustics. (See Resonance, Electrical--Resonator, Electrical.)

Synonym--Nodal Point.

Point Poles. Magnet poles that are virtually points, or of no magnitude. A long thin magnet with little leakage except close to the ends may be supposed to have point poles within itself a short distance back from the ends.

Points, Consequent. In a magnet with consequent poles, the points where such poles are situated.

Points, Corresponding. In bound electrostatic charges the points of equal charges of opposite potentials; the points at opposite extremities of electrostatic lines of force. This definition implies that the bound charges shall be on equal facing areas of conductors, as otherwise the spread or concentration of the lines of force would necessitate the use of areas of size proportionate to the spreading or concentrating of the lines of force. At the same time it may figuratively be applied to these cases, the penetration of the surface by a single line of force including the area fixed by its relation to the surrounding lines.

Points, Isoelectric. In electro-therapeutics, points of equal potential in a circuit.

423 STANDARD ELECTRICAL DICTIONARY.

Points of Derivation. The point where a single conductor branches into two or more conductors, operating or acting in parallel with each other.

Polar Angle. The angle subtended by one of the faces of the pole pieces of the field- magnet of a dynamo or motor. The centre of the circle of the angle lies in the axis of the armature.

Synonym--Angle of Polar Span.

Polar Extension. An addition made of iron to the poles of magnets. Various forms have been experimented with. The pole pieces of dynamo field magnets are polar extensions.

Synonyms--Pole Piece--Polar Tips.

Polarity, Diamagnetic. The induced polarity of diamagnetic substances; it is the reverse of paramagnetic polarity, or of the polarity of iron. A bar of diamagnetic material held parallel with the lines of force in a magnetic field has a like pole induced in the end nearest a given pole of the field magnet, and vice versa. This theory accounts for the repulsion by a magnet of a diamagnetic substance. The existence of this polarity is rather an assumption. It originated with Faraday.

Polarity, Paramagnetic. The induced polarity of paramagnetic substances, such as iron, nickel, or cobalt.

When such a substance is brought into a magnetic field the part nearest a specific pole of a magnet acquires polarity opposite to that of such pole and is thereby attracted.

Another way of expressing it, in which the existence of a pole in or near to the field is not implied, is founded on the conventional direction of lines of force. Where these enter the substance a south pole is formed and where they emerge a north pole is formed.

Such polarity tends always to be established in the direction of greatest length, if the body is free to rotate.

424 STANDARD ELECTRICAL DICTIONARY.

Polarization. (a) The depriving of a voltaic cell of its proper electro-motive force. Polarization may be due to various causes. The solution may become exhausted, as in a Smee battery, when the acid is saturated with zinc and thus a species of polarization follows. But the best definition of polarization restricts it to the development of counter-electro-motive force in the battery by the accumulation of hydrogen on the negative (carbon or copper) plate. To overcome this difficulty many methods are employed. Oxidizing solutions or solids are used, such as solution of chromic acid or powdered manganese dioxide, as in the Bunsen and Leclanché batteries respectively; a roughened surface of platinum black is used, as in the Smee battery; air is blown through the solution to carry off the hydrogen, or the plates themselves are moved about in the solution.

(b) Imparting magnetization to a bar of iron or steel, thus making a permanent magnet, is the polarization of the steel of which it is made. Polarization may be permanent, as in steel, or only temporary, as in soft iron.

(c) The strain upon a dielectric when it separates two oppositely charged surfaces. The secondary discharge of a Leyden jar, and its alteration in volume testify to the strain put upon it by charging.

(d) The alteration of arrangement of the molecules of an electrolyte by a decomposing current. All the molecules are supposed to be arranged with like ends pointing in the same direction, positive ends facing the positively-charged plate and negative ends the negatively-charged one.

(e) The production of counter-electro-motive force in a secondary battery, or in any combination capable of acting as the seat of such counter-electro-motive force. (See Battery, Secondary--Battery, Gas.) The same can be found often in organized cellular tissue such as that of muscles, nerves, or of plants. If a current is passed through this in one direction, it often establishes a polarization or potential difference that is susceptible of giving a return current in the opposite direction when the charging battery is replaced by a conductor.

Polarization Capacity. A voltaic cell in use becomes polarized by its negative plate accumulating hydrogen, or other cause. This gradually gives the plate a positive value, or goes to set up a counter-electro-motive force. The quantity of electricity required to produce the polarization of a battery is termed its Polarization Capacity or Capacity of Polarization.

Polarization of the Medium. The dielectric polarization, q. v., of a dielectric, implying the arrangement of its molecules in chains or filaments; a term due to Faraday. He illustrated it by placing filaments of silk in spirits of turpentine, and introduced into the liquid two conductors. On electrifying one and grounding (or connecting to earth) the other one, the silk filaments arranged themselves in a chain or string connecting the points of the conductors.

Polar Region. That part of the surface of a magnet whence the internal magnetic lines emerge into the air. (S. P. Thompson.) As such lines may emerge from virtually all parts of its surface, the polar regions are indefinite areas, and are properly restricted to the parts whence the lines emerge in greatest quantity.

Polar Span. A proportion of the circle which represents the transverse section of the armature space between the pole pieces of the field magnet in a dynamo or motor; it is the proportion which is filled by the faces of the pole pieces.

425 STANDARD ELECTRICAL DICTIONARY.

Pole, Analogous. The end of a crystal of a pyroelectric substance, such as tourmaline, which end when heated become positively electrified. On reduction of temperature the reverse effect obtains.

Pole, Antilogous. The end of a crystal of a pyroelectric substance, such as tourmaline, which end, while increasing in temperature, becomes negatively electrified. During reduction of its temperature the reverse effect obtains.

Pole Changer. (a) An automatic oscillating or vibrating switch or contact-breaker which in each movement reverses the direction of a current from a battery or other source of current of fixed direction, as such current goes through a conductor.

(b) A switch moved by hand which for each movement effects the above result.

Pole, Negative. (a) In a magnet the south pole; the pole into which the lines of force are assumed to enter from the air or outer circuit.

(b) In a current generator the pole or terminal into which the current is assumed to flow from the external circuit. It is the negatively charged terminal and in the ordinary voltaic battery is the terminal connected to the zinc or positive plate.

Pole Pieces. The terminations of the cores of field or other electro-magnets, or of permanent magnets. These terminations are variously shaped, sometimes being quite large compared to the core proper of the magnet.

They are calculated so as to produce a proper distribution of and direction of the lines of force from pole to pole. As a general rule the active field should be of uniform strength and the pole pieces may be of contour calculated to attain this end.

Pole, Positive. (a) In a magnet the north pole; the pole from which lines of force are assumed to emerge into the air.

(b) In a current generator the pole or terminal whence the current is assumed to issue into the outer circuit. It is the positively charged terminal, and in the ordinary voltaic battery is the terminal connected to the copper or carbon plate, termed the negative plate.

Poles. (a) The terminals of an open electric circuit, at which there necessarily exists a potential difference, produced by the generator or source of electro-motive force in the circuit.

(b) The terminals of an open magnetic circuit; the ends of a magnetized mass of steel, iron or other paramagnetic substance.

(c) The ends in general of any body or mass which show electric or magnetic properties more developed than those of the central sections of the body.

426 STANDARD ELECTRICAL DICTIONARY.

Pole, Salient. In dynamo and motor field magnets, salient poles are those projecting from the base or main body of the field magnet, as distinguished from consequent poles formed by coils wound on the main body itself.

Fig. 268. SALIENT POLES OF FIELD MAGNET.

Poles, Compensating. A device for avoiding the cross-magnetizing effect on the commutator core due to the lead of the brushes. It consists in maintaining a small bar electro-magnet perpendicularly between the pole pieces. This compensates the cross-magnetizing effect.

Poles of Intensity. The locus of highest magnetic force on the earth's surface. One such pole is in Siberia, another is about lat. 52° N., long. 92° W.

[Transcriber's note: 52° N., long. 92° W is about 250 miles Northeast of Winnipeg.]

Poles of Verticity. The magnetic poles of the earth. (See Magnetic Poles.)

Pole Tips. The extreme ends of the expanded poles of a field magnet. In some machines some of the pole tips are made of cast iron, to alter the distribution of the lines of force and resulting magnetic pull upon the armatures. This is done to take off the weight of the armature from its bearings.

Pole, Traveling. A term applied to the poles produced in the action of a rotatory field, whose poles constantly rotate around the circle of the field. (See Field, Rotatory.)

417 STANDARD ELECTRICAL DICTIONARY.

Porous Cup. A cup of pipe clay, unglazed earthenware or other equivalent material used in voltaic cells to keep two liquids separate and yet to permit electrolysis and electrolytic conduction.

They are necessarily only an expedient, as their porous nature permits considerable diffusion, and were they not porous electrolytic action would be impossible.

Synonym--Porous Cell.

Porret's Phenomenon. In electro-physiology, an increase in the diameter of a nerve produced by the positive pole of a voltaic circuit, when placed in contact with the tissue and near to the nerve in question, the other pole being connected to a more or less remote part of the body.

Portelectric Railroad. A railroad worked by solenoidal attraction, the car forming the core of the solenoids. It includes a series of solenoids or hollow coils of copper wire distributed all along the road and inclosing within themselves the track. On this a cylindrical car with pointed ends moves on wheels. Current is supplied to the solenoid in advance of the car, and attracts it. As it advances it breaks the contacts of the attracting solenoid and turns the current into the one next in advance. This operation is repeated as the car advances.

The solenoids are placed close together, each including in the trial track 630 turns of No. 14 copper wire. The car was of wrought iron, 12 feet long, 10 inches in diameter and weighing 500 lbs. It was proposed to employ the system for transportation of mail matter and similar uses.

Position Finder. An instrument for determining the position of objects which are to be fired at from forts. It is designed for use from forts situated on the water.

Fiske's position finder may be thus generally described. On a chart the channel is divided into squares, and the position finder determines the square in which a vessel lies. For each square the direction and elevation of the guns is calculated beforehand. The enemy can therefore be continuously located and fired at, although from smoke or other cause the object may be quite invisible to the gunner.

It comprises two telescopes situated at distant extremities of as long a base line as is obtainable. These telescopes are kept directed upon the object by two observers simultaneously. The observers are in constant telephonic communication. As each telescope moves, it carries a contact over an arc of conducting material. Below each telescope is an arm also moving over an arc of conducting material. These arcs enter into a Wheatstone bridge and are so connected that when the arm and the distant telescope are at the same angle or parallel a balance is obtained. Thus each observer has the power of establishing a balance. A chart is provided for each of them, and over it the arm connected with the distant telescope and an arm or indicator attached to the telescope at that station move so that as long as both telescopes point at the object and each observer maintains the electric balance, the intersection of the arms shows the position on the chart.

The Position Finder is a simplification and amplification of the Range Finder, q. v. In practice the observers may be placed far from the forts, and may telephone their observations thereto. It has been found accurate within one-third of one per cent.

428 STANDARD ELECTRICAL DICTIONARY.

Positive Direction. The direction which lines of force are assumed to take in the air or outer circuit from a positive to a negative region. It applies to electrostatic, to magnetic and to electro-magnetic lines of force.

Positive Electricity. The kind of electricity with which a piece of glass is charged when rubbed with silk; vitreous electricity.

In a galvanic cell the surface of the copper or carbon plate is charged with positive electricity. (See Electrostatic Series.)

According to the single fluid theory positive electrification consists in a surplus of electricity.

[Transcriber's note: "Positive electricity" is a deficiency of electrons.]

Post Office. adj. Many pieces of electric apparatus of English manufacture are thus qualified, indicating that they are of the pattern of the apparatus used by the British Post Office in its telegraph department.

Potential. Potential in general may be treated as an attribute of a point in space, and may express the potential energy which a unit mass would have if placed at that point.

This conception of potential is that of a property attributable to a point in space, such that if a unit mass were placed there the forces acting upon it would supply the force factor of energy, while the body would supply the mass factor. This property is expressible in units, which produce, if the supposed mass is a unit mass, units of work or energy, but potential itself is neither.

Thus taking gravitation, a pound mass on the surface of the earth (assuming it to be a sphere of 4,000 miles radius) would require the expenditure of 21,120,000 foot pounds to remove it to an infinite distance against gravity. The potential of a point in space upon the surface of the earth is therefore negative and is represented by -21,120,000*32.2 foot poundals (32.2 = acceleration of gravity). (See Poundal.) In practice and conventionally all points on the earth's surface are taken as of zero potential.

[Transcriber's note; 21,120,000 foot pounds is about 8 KWh.]

429 STANDARD ELECTRICAL DICTIONARY.

Potential, Absolute. The absolute electrical potential at a point possesses a numerical value and measures the tendency which the existing electric forces would have to drive an electrified particle away from or prevent its approach to the point, if such a particle, one unit in quantity, were brought up to or were situated at that point. It is numerically equal to the number of ergs of work which must be done to bring a positive unit of electricity from a region where there is absolutely no electric force up to the point in question. (Daniell.) Two suppositions are included in this. The region where there is an electric force has to be and only can be at an infinite distance from all electrified bodies. The moving of the particle must take place without any effect upon the distribution of electricity on other particles.

Potential, Constant. Unchanging potential or potential difference.

The ordinary system of incandescent lighting is a constant potential system, an unvarying potential difference being maintained between the two leads, and the current varying according to requirements.

Potential Difference, Electric. If of any two points the absolute potentials are determined, the difference between such two expresses the potential difference. Numerically it expresses the quantity of work which must be done to remove a unit of electricity from one to the other against electric repulsion, or the energy which would be accumulated in moving it the other way.

A positively charged particle is driven towards the point of lower potential. A negatively charged body is driven in the reverse direction.

Potential Difference, Electro-motive. A difference of potential in a circuit, or in part of a circuit, which difference produces or is capable of producing a current, or is due to the flow of such current.

It may be expressed as the fall in potential or the electro-motive force included between any two points on a circuit. The current in an active circuit is due to the total electro-motive force in the circuit. This is distributed through the circuit in proportion to the resistance of its parts. Owing to the distribution of electro-motive force throughout a circuit including the generator, the terminals of a generator on closed circuit may show a difference of potential far lower than the electro-motive force of the generator on closed circuit. Hence potential difference in such a case has been termed available electro-motive force.

Potential, Electric Absolute. The mathematical expression of a property of a point in space, measuring the tendency which existing electric forces would have to drive an electrified unit particle away from or prevent its approach to the point in question, according to whether the point was situated at or was at a distance from the point in question.

Potential is not the power of doing work, although, as it is expressed always with reference to a unit body, it is numerically equal to the number of ergs of work which must be done in order to bring a positive unit of electricity from a region where there is no electric force--which is a region at an infinite distance from all electrified bodies--up to the point in question. This includes the assumption that there is no alteration in the general distribution of electricity on neighboring bodies. (Daniell.)

In practice the earth is arbitrarily taken as of zero electric potential.

430 STANDARD ELECTRICAL DICTIONARY.

Potential, Fall of. The change in potential between any two points on an active circuit. The change in potential due to the maintenance of a current through a conductor.

The fall in potential multiplied by the current gives work or energy units.

The fall of potential in a circuit and its subsequent raising by the action of the generator is illustrated by the diagram of a helix. In it the potential fall in the outer circuit is shown by the descent of the helix. This represents at once the outer circuit and the fall of potential in it. The vertical axis represents the portion of the circuit within the battery or generator in which the potential by the action of the generator is again raised to its original height.

In a circuit of even resistance the potential falls evenly throughout it.

A mechanical illustration of the relation of fall of potential to current is shown in the cut Fig. 269. A vertical wire is supposed to be fixed at its upper end and a lever arm and cord at its lower end, with weight and pulley imparts a torsional strain to it. The dials and indexes show a uniform twisting corresponding to fall of potential. For each unit of length there is a definite loss of twisting, corresponding to fall of potential in a unit of length of a conductor of uniform resistance. The total twisting represents the total potential difference. The weight sustained by the twisting represents the current maintained by the potential difference. For a shorter wire less twisting would be needed to sustain the weight, as in a shorter piece of the conductor less potential difference would be needed to maintain the same current.

Fig. 269. MECHANICAL ILLUSTRATION OF FALL OF POTENTIAL AND CURRENT STRENGTH.

431 STANDARD ELECTRICAL DICTIONARY.

Fig. 270. ILLUSTRATION OF THE FALL AND REDEVELOPMENT OF POTENTIAL IN AN ELECTRIC CIRCUIT.

The fall of potential in a circuit in portions of it is proportional to the resistance of the portions in question. This is shown in the diagram. The narrow lines indicate high and the broad lines low resistance. The fall in different portions is shown as proportional to the resistance of each portion.

Fig. 271. DIAGRAM OF FALL OF POTENTIAL IN A CONDUCTOR OF UNEVEN RESISTANCE.

Potential, Magnetic. The magnetic potential at any point of a magnetic field expresses the work which would be done by the magnetic forces of the field on a positive unit of magnetism as it moves from that point to an infinite distance therefrom. The converse applies to a negative unit.

It is the exact analogue of absolute electric potential.

The potential at any point due to a positive pole m at a distance r is m/r;. that due to a negative pole - m at a distance r' is equal to -m/r';. that due to both is equal to m/r - m/r' or m(1/r - 1/r').

Like electric potential and potential in general, magnetic potential while numerically expressing work or energy is neither, although often defined as such.

432 STANDARD ELECTRICAL DICTIONARY.

Potential, Negative. The reverse of positive potential. (See Potential, Positive.)

Potential, Positive. In general the higher potential. Taking the assumed direction of lines of force, they are assumed to be directed or to move from regions of positive to regions of negative potential. The copper or carbon plate of a voltaic battery is at positive potential compared to the zinc plate.

Potential, Unit of Electric. The arbitrary or conventional potential--or briefly, the potential of a point in an electric field of force--is, numerically, the number of ergs of work necessary to bring a unit of electricity up to the point in question from a region of nominal zero potential--i. e., from the surface of the earth. (Daniell.) This would give the erg as the unit of potential.

Potential, Zero. The potential of the earth is arbitrarily taken as the zero of electric potential.

The theoretical zero is the potential of a point infinitely distant from all electrified bodies.

Fig. 272. DIAGRAM OF POTENTIOMETER CONNECTIONS.

Potentiometer. An arrangement somewhat similar to the Wheatstone Bridge for determining potential difference, or the electro-motive force of a battery. In general principle connection is made so that the cell under trial would send a current in one direction through the galvanometer. Another battery is connected, and in shunt with its circuit the battery under trial and its galvanometer are connected, but so that its current is in opposition. By a graduated wire, like that of a meter bridge, the potential of the main battery shunt can be varied until no current passes. This gives the outline of the method only.

433 STANDARD ELECTRICAL DICTIONARY.

In the cut A B is the graduated potentiometer wire through which a current is passed in the direction of the arrow. E is the battery under trial, placed in opposition to the other current, with a galvanometer next it. Under the conditions shown, if the galvanometer showed no deflection, the E. M. F. of the battery would be to the E. M. F. between the ends of the potentiometer wire, 1 . . . . .10, as 1.5 the distance between the points of connection, A and D of the battery circuit, is to 10, the full length of the potentiometer wire.

Poundal. The British unit of force; the force which acting on a mass of one pound for one second produces an acceleration of one foot.

[Transcriber's note: The force which acting on a mass of one pound produces an acceleration of ONE FOOT PER SECOND PER SECOND.]

Power. Activity; the rate of activity, of doing work, or of expending energy. The practical unit of electric power is the volt-ampere or watt, equal to 1E7 ergs per second. The kilowatt, one thousand watts or volt-amperes, is a frequently adopted unit.

Power, Electric. As energy is the capacity for doing work, electric energy is represented by electricity in motion against a resistance. This possesses a species of inertia, which gives it a species of kinetic energy. To produce such motion, electro- motive force is required. The product of E. M. F. by quantity is therefore electric energy. (See Energy, Electric.)

Generally the rate of energy or power is used. Its dimensions are ( ( (M^.5)*(L^.5) ) / T ) * ( ( (M^.5) *(L^1.5) )/( T^2) ) (intensity or current rate) * (electro-motive force or potential) = (M * (L^2) ) / (T^3), which are the dimensions of rate of work or activity. The practical unit of electric rate of energy or activity is the volt-ampere or watt. By Ohm's law, q. v., we have C = E/R (C = current; E = potential difference or electro-motive force; R = resistance.) The watt by definition = C*E. By substitution from Ohm's formula we deduce for it the following values: ((C^2) * R) and ((E^2) /R). From these three expressions the relations of electric energy to E.M.F., Resistance, and Current can be deduced.

Power of Periodic Current. The rate of energy in a circuit carrying a periodic current. In such a circuit the electro-motive force travels in advance of the current it produces on the circuit. Consequently at phases or intervals where, owing to the alternations of the current, the current is at zero, the electro-motive force may be quite high. At any time the energy rate is the product of the electro-motive force by the amperage. To obtain the power or average rate of energy, the product of the maximum electro-motive force and maximum current must be divided by two and multiplied by the cosine of the angle of lag, which is the angle expressing the difference of phase.

[Transcriber's note; The voltage phase will lead if the load is inductive. The current phase will lead if the load is capacitive. Capacitors or inductors may be introduced into power lines to correct the phase offset introduced by customer loads.]

434 STANDARD ELECTRICAL DICTIONARY.

Pressel. A press-button often contained in a pear-shaped handle, arranged for attachment to the end of a flexible conductor, so as to hang thereby. By pressing the button a bell may be rung, or a distant lamp may be lighted.

Pressure. Force or stress exerted directly against any surface. Its dimensions are force/area or ((M*L)/(T^2)) / (L^2) = M/(L* (T^2)).

Pressure, Electric. Electro-motive force or potential difference; voltage. An expression of metaphorical nature, as the term is not accurate.

Pressure, Electrification by. A crystal of Iceland spar (calcium carbonate) pressed between the fingers becomes positively electrified and remains so for some time. Other minerals act in a similar way. Dissimilar substances pressed together and suddenly separated carry off opposite charges. This is really contact action, not pressure action.

Primary. A term used to designate the inducing coil in an induction coil or transformer; it is probably an abbreviation for primary coil.

Primary Battery. A voltaic cell or battery generating electric energy by direct consumption of material, and not regenerated by an electrolytic process.

The ordinary voltaic cell or galvanic battery is a primary battery.

Prime. vb. To impart the first charge to one of the armatures of a Holtz or other influence machine.

Fig. 273. PRIME CONDUCTOR AND PROOF PLANE.

435 STANDARD ELECTRICAL DICTIONARY.

Prime Conductor. A metal or metal coated sphere or cylinder or other solid with rounded ends mounted on insulating supports and used to collect electricity as generated by a frictional electric machine.

According to whether the prime conductor or the cushions are grounded positive or negative electricity is taken from the ungrounded part. Generally the cushions are grounded, and the prime conductor yields positive electricity.

Probe, Electric. A surgeon's probe, designed to indicate by the closing of an electric circuit the presence of a bullet or metallic body in the body of a patient.

Two insulated wires are carried to the end where their ends are exposed, still insulated from each other. In probing a wound for a bullet if the two ends touch it the circuit is closed and a bell rings. If a bone is touched no such effect is produced. The wires are in circuit with an electric bell and battery.

Projecting Power of a Magnet. The power of projecting its lines of force straight out from the poles. This is really a matter of magnetic power, rather than of shape of the magnet. In electromagnets the custom was followed by making them long to get this effect. Such length was really useful in the regard of getting room for a sufficient number of ampere turns.

436 STANDARD ELECTRICAL DICTIONARY.

Fig. 274. PRONY BRAKE.

Prony Brake. A device for measuring the power applied to a rotating shaft. It consists of a clamping device to be applied more or less rigidly to the shaft or to a pulley upon it. To the clamp is attached a lever carrying a weight. The cut shows a simple arrangement, the shaft A carries a pulley B to which the clamp B1 B2 is applied. The nuts C1 C2 are used for adjustment.

A weight is placed in the pan E attached to the end of the lever D. The weight and clamp are so adjusted that the lever shall stand horizontally as shown by the index E. If we call r the radius of the pulley and F the friction between its surface and the clamp, it is evident that r F, the moment of resistance to the motion of the pulley, is equal to the weight multiplied by its lever arm or to W*R, where W indicates the weight and R the distance of its point of application from the centre of the pulley or r*F = R*W. The work represented by this friction is equal to the distance traveled by the surface of the wheel multiplied by the frictional resistance, or is 2*PI*r*n*F, in which n is the number of turns per minute. But this is equal to 2*PI*R*W. These data being known, the power is directly calculated therefrom in terms of weight and feet per minute.

Proof-plane. A small conductor, usually disc shaped, carried at the end of an insulating handle. It is used to collect electricity by contact, from objects electrostatically charged. The charge it has received is then measured (see Torsion Balance) or otherwise tested. (See Prime Conductor.)

Proof-sphere. A small sphere, coated with gold-leaf or other conductor, and mounted on an insulated handle. It is used instead of a proof-plane, for testing bodies whose curvature is small.

Fig. 275. BOX BRIDGE.

437 STANDARD ELECTRICAL DICTIONARY.

Proportionate Arms. In general terms the arms of a Wheatstone bridge whose proportion has to be known to complete the measurement. There is a different system of naming them. Some designate by this title the two arms in parallel with each other branching at and running from one end of the bridge to the two galvanometer connections. In the cut of the Box Bridge, A C and A B are the proportionate arms. The third arm is then termed the Rheostat arm. (Stewart & Gee.)

Others treat as proportionate arms the two side members of the bridge in parallel with the unknown resistance and third or rheostat arm.

Synonym--Ratio Arms.

Prostration, Electric. Too great exposure to the voltaic arc in its more powerful forms causes symptoms resembling those of sunstroke. The skin is sometimes affected to such a degree as to come off after a few days. The throat, forehead and face suffer pains and the eyes are irritated. These effects only follow exposure to very intense sources of light, or for very long times.

[Transcriber's note: Arcs emit ultraviolet rays.]

Protector, Comb. A lightning arrester, q. v., comprising two toothed plates nearly touching each other.

Protector, Electric. A protective device for guarding the human body against destructive or injurious electric shocks. In one system, Delany's, the wrists and ankles are encircled by conducting bands which by wires running along the arms, back and legs are connected. A discharge it is assumed received by the hands will thus be short circuited around the body and its vital organs. India rubber gloves and shoe soles have also been suggested; the gloves are still used to some extent.

Pull. A switch for closing a circuit when pulled. It is used instead of a push button, q.v., in exposed situations, as its contacts are better protected than those of the ordinary push button.

Pump, Geissler. A form of mercurial air pump. It is used for exhausting Geissler tubes, incandescent lamp bulbs and similar purposes.

Referring to the cut, A is a reservoir of mercury with flexible tube C connected to a tube at its bottom, and raised and lowered by a windlass b, the cord from which passes over a pulley a. When raised the mercury tends to enter the chamber B, through the tube T. An arrangement of stopcocks surmounts this chamber, which arrangement is shown on a larger scale in the three figures X, Y and Z. To fill the bulb B, the cocks are set in the position Z; n is a two way cock and while it permits the escape of air below, it cuts off the tube, rising vertically from it. This tube, d in the full figure connects with a vessel o, pressure gauge p, and tube c, the latter connecting with the object to be exhausted. The bulb B being filled, the cock m is closed, giving the position Y and the vessel A is lowered until it is over 30 inches below B.

438 STANDARD ELECTRICAL DICTIONARY.

This establishes a Torricellian vacuum in B. The cock n is now turned, giving the position X, when air is at once exhausted from the vessel connected to C. This process is repeated until full exhaustion is obtained. In practice the first exhaustion is often effected by a mechanical pump. By closing the cock on the outlet tube c but little air need ever find its way to the chambers o and B.

Fig. 276. GEISSLER AIR PUMP.

439 STANDARD ELECTRICAL DICTIONARY.

Pumping. In incandescent lamps a periodical recurring change in intensity due to bad running of the dynamos, or in arc lamps to bad feeding of the carbons.

Fig. 277. SPRENGEL AIR PUMP.

Pump, Sprengel. A form of mercurial air pump. A simple form is shown in the cut. Mercury is caused to flow from the funnel A, through c d to a vessel B. A side connection x leads to the vessel R to be exhausted. As the mercury passes x it breaks into short columns, and carries air down between them, in this way exhausting the vessel R. In practice it is more complicated. It is said to give a better vacuum than the Sprengel pump, but to be slower in action.

440 STANDARD ELECTRICAL DICTIONARY.

Pump, Swinburne. A form of mechanical air pump for exhausting incandescent lamp bulbs. Referring to the cut, A is a bulb on the upper part of a tube G; above A are two other bulbs C and D. From the upper end a tube runs to the bulb E. Through the cock L, and tube F connection is made with a mechanical air pump. The tube H leads to a drying chamber I, and by the tube J connects with the lamp bulbs or other objects to be exhausted. The tube G enters the bottle B through an airtight stopper, through which a second tube with stopcock K passes. In use a vacuum is produced by the mechanical pumps, exhausting the lamp bulbs to a half inch and drawing up the mercury in G. The bent neck in the bulb E, acts with the bulb as a trap to exclude mercury from F. When the mechanical pumps have produced a vacuum equal to one half inch of mercury, the cock L is closed and K is opened, and air at high pressure enters. This forces the mercury up to the vessel D, half filling it. The high pressure is now removed and the mercury descends. The valve in D closes it as the mercury falls to the level G. Further air from the lamps enters A, and by repetition of the ascent of the mercury, is expelled, through D. The mercury is again lowered, producing a further exhaustion, and the process is repeated as often as necessary.

Fig. 278. SWINBURNE'S AIR PUMP.

Push-Button. A switch for closing a circuit by means of pressure applied to a button. The button is provided with a spring, so that when pushed in and released it springs back. Thus the circuit is closed only as long as the button is pressed. The electric connection may be made by pressing together two flat springs, each connected to one of the wires, or by the stem of the button going between two springs, not in contact, forcing them a little apart to secure good contact, and thereby bridging over the space between them.

441 STANDARD ELECTRICAL DICTIONARY.

Pyro-electricity. A phenomenon by which certain minerals when warmed acquire electrical properties. (Ganot.) The mineral tourmaline exhibits it strongly. It was originally observed in this mineral which was found to first attract and then to repel hot ashes.

The phenomenon lasts while any change of temperature within certain limits is taking place. In the case of tourmaline the range is from about 10º C. (50º F.) to 150º C. (302º F.) Above or below this range it shows no electrification.

The effect of a changing of temperature is to develop poles, one positive and the other negative. As the temperature rises one end is positive and the other negative; as the temperature becomes constant the polarity disappears; as the temperature falls the poles are reversed.

If a piece of tourmaline excited by pyro-electricity is broken, its broken ends develop new poles exactly like a magnet when broken.

The following minerals are pyro-electric: Boracite, topaz, prehnite, zinc silicate, scolezite, axenite. The following compound substances are also so: Cane sugar, sodium- ammonium racemate and potassium tartrate.

The list might be greatly extended.

The phenomenon can be illustrated by sifting through a cotton sieve upon the excited crystal, a mixture of red lead and flowers of sulphur. By the friction of the sifting these become oppositely electrified; the sulphur adheres to the positively electrified end, and the red lead to the negatively electrified end. (See Analogous Pole-Antilogous Pole.)

Pyromagnetic Motor. A motor driven by the alternation of attraction and release of an armature or other moving part, as such part or a section of it is rendered more or less paramagnetic by heat.

Thus imagine a cylinder of nickel at the end of a suspension rod, so mounted that it can swing like a pendulum. A magnet pole is placed to one side to which it is attracted. A flame is placed so as to heat it when in contact with the magnet pole. This destroys its paramagnetism and it swings away from the magnet and out of the flame. It cools, becomes paramagnetic, and as it swings back is reattracted, to be again released as it gets hot enough. This constitutes a simple motor.

A rotary motor may be made on the same lines. Nickel is particularly available as losing its paramagnetic property easily.

442 STANDARD ELECTRICAL DICTIONARY.

Various motors have been constructed on this principle, but none have attained any practical importance. Owing to the low temperature at which it loses its paramagnetic properties nickel is the best metal for paramagnetic motors.

In Edison's motor, between the pole pieces of an electro-magnet a cylinder made up of a bundle of nickel tubes is mounted, so as to be free to rotate. A screen is placed so as to close or obstruct the tubes farthest from the poles. On passing hot air or products of combustion of a fire or gas flame through the tubes, the unscreened ones are heated most and lose their paramagnetism. The screened tubes are then attracted and the armature rotates, bringing other tubes under the screen, which is stationary. Then the attracted tubes are heated while the others cool, and a continuous rotation is the result.

Fig. 279. EDISON'S PYROMAGNETIC MOTOR.

Pyromagnetic Generator. A current generator producing electric energy directly from thermal energy by pyromagnetism.

Edison's pyromagnetic generator has eight electro-magnets, lying on eight radii of a circle, their poles facing inward and their yokes vertical. Only two are shown in the cut. On a horizontal iron disc are mounted eight vertical rolls of corrugated nickel representing armatures. On each armature a coil of wire, insulated from the nickel by asbestus is wound. The coils are all in series, and have eight connections with a commutator as in a drum armature. There are two main divisions to the commutator. Each connects with an insulated collecting ring, and the commutator and collecting rings are mounted on a spindle rotated by power. Below the circle of vertical coils is a horizontal screen, mounted on the spindle and rotating with it.

A source of heat, or a coal stove is directly below the machine and its hot products of combustion pass up through the coils, some of which are screened by the rotating screen. The effect is that the coils are subjecting to induction owing to the change in permeability of the nickel cores, according as they are heated, or as they cool when the screen is interposed. The two commutator segments are in constant relation to the screen, and current is collected therefrom and by the collecting rings is taken to the outside circuit.

443 STANDARD ELECTRICAL DICTIONARY.

Pyromagnetism. The development of new magnetic properties or alteration of magnetic sensibility in a body by heat. Nickel and iron are much affected as regards their paramagnetic power by rise of temperature.

Fig. 280. PYROMAGNETIC GENERATOR.

Pyrometer, Siemens' Electric. An instrument for measuring high temperatures by the variations in electric resistance in a platinum wire exposed to the heat which is to be measured.

Q. Symbol for electric quantity.

Quad. (a) A contraction for quadrant, used as the unit of inductance; the henry.

(b) A contraction for quadruplex in telegraphy.

[Transcriber's note: A modern use of "quad" is a unit of energy equal to 1E15 (one quadrillion) BTU, or 1.055E18 joules. Global energy production in 2004 was 446 quad.]

Quadrant. A length equal to an approximate earth quadrant, equal to 1E9 centimeters. It has been used as the name for the unit of inductance, the henry, q. v.

Synonym--Standard Quadrant.

444 STANDARD ELECTRICAL DICTIONARY.

Quadrant, Legal. The accepted length of the quadrant of the earth, 9.978E8 instead of 1E9 centimeters; or to 9,978 kilometers instead of 10,000 kilometers.

Quadrature. Waves or periodic motions the angle of lag of one of which, with reference to one in advance of it, is 90°, are said to be in quadrature with each other.

[Transcriber's note: If the voltage and current of a power line are in quadrature, the power factor is zero (cos(90°) = 0) and no real power is delivered to the load.]

Qualitative. Involving the determination only of the presence or absence of a substance or condition, without regard to quantity. Thus a compass held near a wire might determine qualitatively whether a current was passing through the wire, but would not be sufficient to determine its quantity. (See Quantitative.)

Quality of Sound. The distinguishing characteristic of a sound other than its pitch; the timbre.

It is due to the presence with the main or fundamental sound of other minor sounds called overtones, the fundamental note prevailing and the other ones being superimposed upon it. The human voice is very rich in overtones; the telephone reproduces these, thus giving the personal peculiarities of every voice.

Synonym--Timbre.

Quantitative. Involving the determination of quantities. Thus a simple test would indicate that a current was passing through a wire. This would be a qualitative test. If by proper apparatus the exact intensity of the current was determined, it would be a quantitative determination. (See Qualitative.)

Quantity. This term is used to express arrangements of electrical connections for giving the largest quantity of current, as a quantity armature, meaning one wound for low resistance.

A battery is connected in quantity when the cells are all in parallel. It is the arrangement giving the largest current through a very small external resistance.

The term is now virtually obsolete (Daniell); "in surface," "in parallel," or "in multiple arc" is used.

Quantity, Electric. Electricity may be measured as if it were a compressible gas, by determining the potential it produces when stored in a defined recipient. In this way the conception of a species of quantity is reached. It is also measured as the quantity of current passed by a conductor.

Thus a body whose surface is more or less highly charged with electricity, is said to hold a greater or less quantity of electricity.

It may be defined in electrostatic or electro-magnetic terms. (See Quantity, Electrostatic--Quantity, Electro-magnetic.)

445 STANDARD ELECTRICAL DICTIONARY.

Quantity. Electro-magnetic. Quantity is determined electro-magnetically by the measurement of current intensity for a second of time: its dimensions are therefore given by multiplying intensity or current strength by time. The dimensions of intensity are ( (M^.5) * (L^.5) ) / T therefore the dimensions of electro-magnetic quantity are ( ( (M^.5) * (L^.5) ) / T ) * T = ( (M^.5) * (L^.5) )

Quantity, Electro-magnetic, Practical Unit of. The quantity of electricity passed by a unit current in unit time; the quantity passed by one ampere in one second; the coulomb.

It is equal to 3E9 electrostatic absolute units of quantity and to 0.1 of the electro- magnetic absolute unit of quantity.

One coulomb is represented by the deposit of .00111815 gram, or .017253 grain of silver, .00032959 gram, or .005804 grain of copper, .0003392 gram, or .005232 grain of zinc.

If water is decomposed by a current each coulomb is represented by the cubic centimeters of the mixed gases (hydrogen and oxygen) given by the following formula. ( 0.1738 * 76 * (273 + Cº ) ) / ( h * 273 ) in which Cº is the temperature of the mixed gases in degree centigrade and h is the pressure in centimeters of mercury column; or by ( 0.01058 * 30 (491 + Fº - 32) ) / (h * 491 ) for degrees Fahrenheit and inches of barometer.

[Transcriber's note: 6.24150962915265E18 electrons is one coulomb.]

Quantity, Electrostatic. Quantity is determined electro-statically by the repulsion a charge of given quantity exercises upon an identical charge at a known distance. The force evidently varies with the product of the two quantities, and by the law of radiant forces also inversely with the square of the distance. The dimensions given by these considerations is Q * Q/(L*L). This is the force of repulsion. The dimensions of a force are (M * L) /(T^2). Equating these two expressions we have: (Q^2)/(L^2) = (M*L)/(T^2) or Q = ((M^.5)*(L^1.5)) / T which are the dimensions of electrostatic quantity.

Quantity, Meter. An electric meter for determining the quantity of electricity which passes through it, expressible in coulombs or ampere hours. All commercial meters are quantity meters.

446 STANDARD ELECTRICAL DICTIONARY.

Quartz. A mineral, silica, SiO2. It has recently been used by C. V. Boys and since by others in the making of filaments for torsion suspensions. The mineral is melted, while attached to an arrow or other projectile. It is touched to another piece of quartz or some substance to which it adheres and the arrow is fired off from the bow. A very fine filament of surpassingly good qualities for galvanometer suspension filaments is produced.

As a dielectric it is remarkable in possessing but one-ninth the residual capacity of glass.

Quicking. The amalgamating of a surface of a metallic object before silver plating. It secures better adhesion of the deposit. It is executed by dipping the article into a solution of a salt of mercury. A solution of mercuric nitrate 1 part, in water 100 parts, both by weight, is used.

R. (a) Abbreviation and symbol for Reamur, as 10º R., meaning 10º by the Reamur thermometer. (See Reamur Scale.)

(b) Symbol for resistance, as in the expression of Ohm's Law C=E/R. (rho, Greek r) Symbol for specific resistance.

Racing of Motors. The rapid acceleration of speed of a motor when the load upon it is removed. It is quickly checked by counter-electro-motive force. (See Motor, Electric.)

Radian. The angle whose arc is equal in length to the radius; the unit angle.

Radiant Energy. Energy, generally existing in the luminiferous ether, kinetic and exercised in wave transmission, and rendered sensible by conversion of its energy into some other form of energy, such as thermal energy.

If the ether waves are sufficiently short and not too short, they directly affect the optic nerve and are known as light waves; they may be so short as to be inappreciable by the eye, yet possess the power of determining chemical change, when they are known as actinic waves; they may be also so long as to be inappreciable by the eye, when they may be heat-producing waves, or obscure waves.

Other forms of energy may be radiant, as sound energy dispersed by the air, and gravitational energy, whose connection with the ether has not yet been demonstrated.

Radiation. The traveling or motion of ether waves through space.

[Transcriber's note: The modern term corresponding to this definition is photons. The modern concept of radiation also includes particles-- neutrons, protons, alpha (helium) and beta (electrons) rays and other exotic items.]

Radicals. A portion of a molecule, possessing a free bond and hence free to combine directly. A radical never can exist alone, but is only hypothetical. An atom is a simple radical, an unsaturated group of atoms is a compound radical.

447 STANDARD ELECTRICAL DICTIONARY.

Radiometer. An instrument consisting of four vanes poised on an axis so as to be free to rotate, and contained in a sealed glass vessel almost perfectly exhausted. The vanes of mica are blackened on one side.

On exposure to light or a source of heat (ether waves) the vanes rotate. The rotation is due to the beating back and forth of air molecules from the surface of the vanes to the inner surface of the glass globe.

Radiometer, Electric. A radiometer in which the motion of the molecules of air necessary for rotation of the vane is produced by electrification and not by heating.

Radio-micrometer. An instrument for detecting radiant energy of heat or light form. It consists of a minute thermopile with its terminals connected by a wire, the whole suspended between the poles of a magnet. A minute quantity of heat produces a current in the thermopile circuit, which, reacted on by the field, produces a deflection. A convex mirror reflecting light is attached so as to move with the thermopile. The instrument is of extraordinary sensitiveness. It responds to .5E-6 of a degree Centigrade or about 1E-6 degree Fahrenheit.

Radiophony. The production of sound by intermittent action of a beam of light upon a body. With possibly a few exceptions all matter may produce sound by radiophouy.

Range Finder. An apparatus for use on shipboard to determine the distance of another ship or object. It is designed for ships of war, to give the range of fire, so as to set the guns at the proper elevation. The general principle involved is the use of the length of the ship if possible, if not of its width, as a base line. Two telescopes are trained upon the object and kept trained continuously thereon. The following describes the Fiske range finder.

The range finder comprises two fairly powerful telescopes, each mounted on a standard, which can be rotated round a vertical axis, corresponding with the center of the large disc shown in the engraving. One-half of the edge of this disc is graduated to 900 on either side of a zero point, and below the graduation is fixed a length of platinum silver wire. This wire only extends to a distance of 81.10 on either side of zero, and is intended to form two arms of a Wheatstone bridge. The sliding contact is carried by the same arm as the telescope standards, so that it moves with the telescope. The two instruments are mounted at a known distance apart on the ship, as shown diagrammatically in the cut. Here A and B are the centers of the two discs, C and D the arms carrying the telescopes, and E and F the platinum silver wires. Suppose the object is at T, such that A B T is a right angle, then AT=AB/sin(ATB).

448 STANDARD ELECTRICAL DICTIONARY.

If the two sectors are coupled up as shown, with a battery, h, and a galvanometer, by the wires, a b and c d, then since the arm, e, on being aligned on the object takes the position c1 while d remains at zero, the Wheatstone bridge formed by these segments and their connections will be out of balance, and a current will flow through the galvanometer, which may be so graduated as to give the range by direct reading, since the current through it will increase with the angle A T B.

Fig. 281. RANGE FINDER.

In general, however, the angle A B T will not be a right angle, but some other angle. In this case AT = AB / sin(A T B) * sin( A B T), and hence it will only be necessary to multiply the range reading on the galvanometer by the sine of the angle A B T, which can be read directly by the observer at B. This multiplication is not difficult, but by suitably arranging his electrical appliances Lieutenant Fiske has succeeded in getting rid of it, so that the reading of the galvanometer always gives the range by direct reading, no matter what the angle at B may be. To explain this, consider the two telescopes shown in the cut in the positions C and D; the whole current then has a certain resistance.

449 STANDARD ELECTRICAL DICTIONARY.

Next suppose them, still remaining parallel, in the positions C1 and D1. The total resistance of the circuit is now less than before, and hence if C1, one of the telescopes, is moved out of parallel to the other, through a certain angle, the current through the galvanometer will be greater than if it were moved through an equal angle out of a parallel when the telescopes were in the positions C and D. The range indicated is, therefore, decreased, and by properly proportioning the various parts it is found that the range can always be read direct from the galvanometer, or in other words the multiplication of A B/sin( A T B ) by sin( A B T ) is to all intents and purposes performed automatically. There is, it is true, a slight theoretical error; but by using a small storage battery and making the contents carefully it is said to be inappreciable. Each telescope is fitted with a telephone receiver and transmitter, so that both observers can without difficulty decide on what point to align their telescopes. It will be seen that it is necessary that the lines of sight of two telescopes should be parallel when the galvanometer indicates no current. It has been proposed to accomplish this by sighting both telescopes on a star near the horizon, which being practically an infinite distance away insures the parallelism of the lines of sight.

Rate Governor. An apparatus for securing a fixed rate of vibration of a vibrating reed. It is applied in simultaneous telegraphy and telephoning over one wire. The principle is that of the regular make and break mechanism, with the feature that the contact is maintained during exactly one-half of the swing of the reed. The contact exists during the farthest half of the swing of the reed away from the attracting pole.

Fig. 282. LANGDON DAVIRS' RATE GOVERNOR.

In the left hand figure of the cut, K is the key for closing the circuit. A is the base for attachment of the reed. V is the contact-spring limited in its play to the right by the screw S. C is the actuating magnet. By tracing the movements of the reed, shown on an exaggerated scale in the three right hand figures, it will be seen that the reed is in electric contact with the spring during about one-half its movement. The time of this connection is adjustable by the screw S.

Synonym--Langdon Davies' Rate Governor or Phonophone.

450 STANDARD ELECTRICAL DICTIONARY.

Ray, Electric. Raia torpedo. The torpedo, a fish having the same power of giving electric shocks as that possessed by the electric eel, q. v. (See also Animal Electricity.)

Fig. 283. TORPEDO OR ELECTRIC RAY

Reaction of Dynamo, Field and Armature. A principle of the dynamo current generator, discovered by Soren Hjorth of Denmark.

When the armature is first rotated it moves in a field due to the residual magnetism of the field magnet core. This field is very weak, and a slight current only is produced. This passing in part or in whole through the field magnet cores slightly strengthens the field, whose increased strength reacts on the armature increasing its current, which again strengthens the field. In this way the current very soon reaches its full strength as due to its speed of rotation.

The operation is sometimes termed building up.

Sometimes, when there is but a trace of residual magnetism, it is very hard to start a dynamo.

Reading Telescope. A telescope for reading the deflections of a reflecting galvanometer.

A long horizontal scale is mounted at a distance from the galvanometer and directly below or above the centre of the scale a telescope is mounted. The telescope is so directed that the mirror of the galvanometer is in its field of view, and the relative positions of mirror, scale and telescope are such that the image of the scale in the galvanometer mirror is seen by the observer looking through the telescope.

Under these conditions it is obvious that the graduation of the scale reflected by the mirror corresponds to the deflection of the galvanometer needle.

The scale may be straight or curved, with the galvanometer in the latter case, at its centre of curvature.

Reamur Scale. A thermometer scale in use in some countries of Continental Europe. The temperature of melting ice is 0°; the temperature of condensing steam is 80°; the degrees are all equal in length. For conversion to centigrade degrees multiply degrees Reamur by 5/4. For conversion to Fahrenheit degrees multiply by 9/4 and add 32 if above 0° R., and if below subtract 32. Its symbol is R., as 10° R.

451 STANDARD ELECTRICAL DICTIONARY.

Recalescence. A phenomenon occurring during the cooling of a mass of steel, when it suddenly emits heat and grows more luminous for an instant. It is a phase of latent heat, and marks apparently the transition from a non-magnetizable to a magnetiz able condition.

Receiver. In telephony and telegraphy, an instrument for receiving a message as distinguished from one used for sending or transmitting one.

Thus the Bell telephone applied to the ear is a receiver, while the microphone which is spoken into or against is the transmitter.

Receiver, Harmonic. A receiver including an electro-magnet whose armature is an elastic steel reed, vibrating to a particular note. Such a reed responds to a series of impulses succeeding each other with the exact frequency of its own natural vibrations, and does not respond to any other rapid series of impulses. (See Telegraph Harmonic.)

Reciprocal. The reciprocal of a number is the quotient obtained by dividing one by the number. Thus the reciprocal of 8 is 1/8.

Applied to fractions the above operation is carried out by simply inverting the fraction. Thus the reciprocal of 3/4 is 4/3 or 1-1/3.

Record, Telephone. Attempts have been made to produce a record from the vibrations of a telephone disc, which could be interpreted by phonograph or otherwise.

Fig. 284. MORSE RECORDER OR EMBOSSER.

452 STANDARD ELECTRICAL DICTIONARY.

Recorder, Morse. A telegraphic receiving apparatus for recording on a strip of paper the dots and lines forming Morse characters as received over a telegraph line. Its general features are as follows:

A riband or strip of paper is drawn over a roller which is slightly indented around its centre. A stylus or blunt point carried by a vibrating arm nearly touches the paper. The arm normally is motionless and makes no mark on the paper. An armature is carried by the arm and an electro-magnet faces the armature. When a current is passed through the magnet the armature is attracted and the stylus is forced against the paper, depressing it into the groove, thus producing a mark. When the current ceases the stylus is drawn back by a spring.

Fig. 285. INKING ROLLER MECHANISM OF MORSE RECORDER.

In some instruments a small inking roller takes the place of the stylus, and the roller is smooth. The cut, Fig. 285, shows the plan view of the ink-roller mechanism. J is the roller, L is the ink well, Cl is the arm by which it is raised or lowered by the electro-magnet, as in the embosser. S S is the frame of the instrument, and B the arbor to which the arm carrying the armature is secured, projecting to the right. A spring is arranged to rub against the edge of the inking roller and remove the ink from it.

The paper is fed through the apparatus by clockwork. At the present day sound reading has almost entirely replaced the sight reading of the recorder.

Recorder, Siphon. A recording apparatus in which the inked marks are made on a strip of paper, the ink being supplied by a siphon terminating in a capillary orifice.

In the cut N S represents the poles of a powerful electro-magnet. A rectangular coil bb of wire is suspended between the coils. A stationary iron core a intensifies the field. The suspension wire f f 1 has its tension adjusted at h. This wire acts as conductor for the current.

453 STANDARD ELECTRICAL DICTIONARY.

The current is sent in one or the other direction or is cut off in practice to produce the desired oscillations of the coil b b. A glass siphon n l works upon a vertical axis l. One end l is immersed in an ink well m. Its longer end n touches a riband of paper o o. The thread k attached to one side of the coil pulls the siphon back and forth according to the direction of current going through the electro-magnet cores. A spiral spring adjusted by a hand-screw controls the siphon. In operation the siphon is drawn back and forth producing a zigzag line. The upward marks represent dots, the downward ones dashes. Thus the Telegraphic Code can be transmitted on it. To cause the ink to issue properly, electrification by a static machine has been used, when the stylus does not actually touch the paper, but the ink is ejected in a series of dots.

Fig. 286. SIPHON RECORDER.

Reducteur for Ammeter. A resistance arranged as a shunt to diminish the total current passing through an ammeter. It is analogous to a galvanometer shunt. (See Multiplying Power of Shunt.)

Reducteur for Voltmeter. A resistance coil connected in series with a Voltmeter to diminish the current passing through it. Its resistance being known in terms of the resistance of the voltmeter it increases the range of the instrument so that its readings may cover double or more than double their normal range.

Reduction of Ores, Electric. Treatment of ores by the electric furnace (see Furnace, Electric.) The ore mixed with carbon and flux is melted by the combined arc and incandescent effects of the current and the metal separates. In another type the metal is brought into a fusible compound which is electrolyzed while fused in a crucible. Finally processes in which a solution of a salt of the metal is obtained, from which the metal is obtained by electrolysis, may be included. Aluminum is the metal to whose extraction the first described processes are applied.

454 STANDARD ELECTRICAL DICTIONARY.

Refraction, Electric Double. Double refraction induced in some materials by the action of either an electrostatic, magnetic or an electro-magnetic field.

The intensity or degree of refracting power is proportional to the square of the strength of field.

Refreshing Action. In electro-therapeutics the restoration of strength or of nerve force by the use of voltaic alternatives, q. v.

Region, Extra-polar. In electro-therapeutics the area or region of the body remote from the therapeutic electrode.

Region, Polar. In electro-therapeutics the area or region of the body near the therapeutic electrode.

Register, Electric. There are various kinds of electric registers, for registering the movements of watchmen and other service. Contact or press buttons may be distributed through a factory. Each one is connected so that when the circuit is closed thereby a mark is produced by the depression of a pencil upon a sheet or disc of paper by electro-magnetic mechanism. The paper is moved by clockwork, and is graduated into hours. For each push-button a special mark may be made on the paper. The watchman is required to press the button at specified times. This indicates his movements on the paper, and acts as a time detector to show whether he has been attending to his duty.

Register, Telegraphic. A term often applied to telegraph recorders, instruments for producing on paper the characters of the Morse or other alphabet.

Regulation, Constant Current. The regulation of a dynamo so that it shall give a constant current against any resistance in the outer circuits, within practical limits. It is carried out in direct current machines generally by independent regulators embodying a controlling coil with plunger or some equivalent electro-magnetic device inserted in the main circuit and necessarily of low resistance. In some regulators the work of moving the regulator is executed mechanically, but under electrical control; in others the entire work is done by the current.

A typical regulator or governor (Golden's) of the first class comprises two driven friction wheels between which is a driving friction wheel, which can engage with one driven wheel only at once. It is brought into engagement with one or the other by a solenoid and plunger.

455 STANDARD ELECTRICAL DICTIONARY.

As it touches one wheel it turns it in one direction. This moves a sliding contact in one direction so as to increase a resistance. This corresponds to a motion of the plunger in one direction. As the driving wheel moves in the opposite direction by a reverse action it diminishes the resistance. Thus the increase and decrease of resistance correspond to opposite movements of the solenoid plunger, and consequently to opposite variations in the current. The whole is so adjusted that the variations in resistance maintain a constant amperage. The resistance is in the exciting circuit of the dynamo.

In Brush's regulator, which is purely mechanical, a series dynamo is made to give a constant current by introducing across the field magnets a shunt of variable resistance, whose resistance is changed by an electro-magnet, whose coils are in circuit with the main current. Carbon resistance discs are used which the electro-magnet by its attraction for its armature, presses with varying intensity. This alters the resistance, decreasing it as the current increases and the reverse. As the connection is in shunt this action goes to maintain a constant current.

Regulation, Constant Potential. The regulation of constant potential dynamos is executed on the same lines as that of constant current dynamos. If done by a controlling coil, it must for constant potential regulation be wound with fine wire and connected as a shunt for some part of the machine.

Regulation of Dynamos. The regulation of dynamos so that they shall maintain a constant potential difference in the leads of their circuit for multiple arc systems or shall deliver a constant current in series systems. Hence two different systems of regulation are required, (a) constant potential regulation--(b) constant current regulation. The first named is by far the more important, as it concerns multiple arc lighting, which is the system universally used for incandescent lighting.

S. P. Thompson thus summarizes the methods of governing or regulating dynamos. Premising that alteration of the magnetic flux is the almost universal way of control, it can be done in two ways; first, by varying the excitation or ampere turns of the field, and second by varying the reluctance of the magnetic circuit. The excitation or magnetic flux may be varied

(a) by hand, with the aid of rheostats and commutators in the exciting circuit;

(b) automatically, by governors, taking the place of the hand;

(c) by compound windings. The magnetic circuit may have its reluctance caused to vary in several ways;

(d) by moving the pole pieces nearer to or further from the armature;

(e) by opening or closing some gap in the magnetic circuit (field-magnet core);

(f) by drawing the armature endways from between the pole pieces;

(g) by shunting some of the magnetic lines away from the armature by a magnetic shunt.

The latter magnetic circuit methods d, e, f, and g, have never met with much success except on small machines or motors. Method e is adopted in the Edison motor, the yoke being withdrawn or brought nearer the cores of the coils. (See Regulation, Constant Current-Regulation, constant Potential.)

456 STANDARD ELECTRICAL DICTIONARY.

Reguline. adj. Having the characteristics of a piece of metal, being flexible, adherent, continuous, and coherent. Applied to electrolytic deposits.

Relative. Indicating the relation between two or more things without reference to absolute value of any one of them. Thus one lamp may be of relatively double resistance compared to another, but this states nothing of the resistance in ohms of either lamp.

Relay. A receiving instrument which moves in accordance with impulses of currents received, and in so moving opens and closes a local circuit, which circuit may include as powerful a battery as required or desirable, while the relay may be on the other hand so delicate as to work with a very weak current.

Fig. 287. RELAY.

The typical relay includes an electro-magnet and armature. To the latter an arm is attached and the lower end of the arm works in pivots. As the armature is attracted the arm swings towards the magnet. When the current is cut off, the armature and arm are drawn back by a spring. When the arm swings towards the magnet its upper end touching a contact screw closes the local circuit. When it swings back it comes in contact with a second screw, with insulated point, and opens the circuit as it leaves the first named screw.

One terminal connects with the arm through the pivots and frame. The other connects with the contact screw through the frame carrying it.

Synonym--Relay Magnet.

457 STANDARD ELECTRICAL DICTIONARY.

Relay Bells. Bells connected by relay connection to a main line for acoustic telegraphy. A stroke on one bell indicates a dot and on the other a dash. The system is now nearly extinct.

Relay, Box-sounding. A relay which is surrounded by or mounted on a resonator or wooden box of such proportions and size as to reinforce the sound. This enables a relay to act as a sounder, its weak sounds being virtually magnified so as to be audible.

Relay Connection. A connection used in telegraphy, including a local battery, with a short circuit normally open, but closed by a switch and a sounder or other appliance. The latter is made very sensitive so as to be worked by a feeble current, and is connected to the main line. A very slight current closes the switch and the local battery comes into operation to work a sounder, etc. When the current ceases on the main line the switch opens and throws the local battery out of action. The switch is termed a relay, q. v. A long main line may thus produce strong effects at distant stations, the intensity of action depending on the local battery.

Fig. 288. RELAY OR LOCAL CIRCUIT.

Relay, Differential. A relay containing two coils wound differentially, and of the same number of turns and resistance. If two equal currents pass through the coils they counteract each other and no action takes place. If there is a difference in the currents the relay acts as one coil preponderates. The coils may be wound for uneven currents with different resistance and number of turns.

Relay, Microphone. A relay connection applied to a telephone circuit. It consists of a microphone mounted in front of the diaphragm of a telephone receiver. In circuit with the microphone is a battery and second telephone receiver. The microphone is supposed to intensify the sounds of the first telephone.

458 STANDARD ELECTRICAL DICTIONARY.

Relay, Polarized. A relay whose armature is of steel, and polarized or permanently magnetized, or in which a permanent magnet is used as the basis for the electro-magnets. In the relay shown in the cut the coils shown are mounted on cores carried on the end of a powerful bent permanent magnet. Thus when no current passes their upper poles are both of the same sign, and the horizontally vibrating tongue is held by the magnetic attraction against one or the other pole piece. If a current is sent through the electro-magnet it gives opposite polarity to the two polar extensions. As the end of the vibrating tongue is of polarity determined by the permanent magnet it is attracted to one pole and repelled from the other. On cessation of current it remains attached by the permanent magnetism. If now a current is sent in the opposite direction the two poles again acquire opposite polarity, the reverse of the former, and the tongue flies across to the opposite side. On cessation of current it remains attached as before by the permanent magnetism.

In its movements to and fro the relay tongue opens and closes a contact, so as to work a sounder or other apparatus. The polarized relay is of high sensibility, and requires little or no change of adjustment.

Fig. 288. POLARIZED RELAY

Reluctance. In a magnetic circuit or portion thereof, the resistance offered to the flow of lines of force. The magnetic circuit as has already been stated is treated like an electric circuit, and in it reluctance occupies the place of resistance in the electric circuit. It is the reciprocal of permeance. S. P. Thompson expresses the law thus:

Total number of magnetic lines = (magneto-motive force) / (magnetic reluctance)

Synonyms--Magnetic Reluctance-Magnetic Resistance.

Reluctance, Unit of. The reluctance of a circuit through which unit magnetizing power (magneto-motive force) can produce a unit of induction or one line of force. This value is very high; the reluctance of ordinary magnetic circuits ranges from 1E-5 to 1E-8 unit of reluctance.

Reluctivity. Specific reluctance; the reluctance of a cube of material whose edge measures one centimeter in length. It is a quality bearing the same relation to reluctance that permeability does to permeance.

It is defined as the reciprocal of magnetic permeability. (Kenelly.) If plotted as a curve for different values of the magnetizing force it is found to be nearly a straight line, a linear function of the magnetizing force, H with the equation a + b H. Reluctivity is the property of a substance; reluctance is the property of a circuit.

459 STANDARD ELECTRICAL DICTIONARY.

Remanence. The residual magnetism left after magnetic induction, expressed in lines of force per square centimeter.

Repeater. In telegraphy an instrument for repeating the signals through a second line. It is virtually a relay which is operated by the sender, and which in turn operates the rest of the main line, being situated itself at about the middle point of the distance covered. In the simpler forms of repeater two relays are used, one for transmission in one direction the other for transmission in the other. An attendant switches one or the other in as required.

Thus a common relay is virtually a repeater for its local circuit. If such a relay is placed half way down a line, and if the line beyond it is connected as its local, it becomes a repeater.

Some forms of repeaters are automatic, and repeat both ways without the need of an attendant.

It is the practice to somewhat prolong the signals sent through a repeater.

Replenisher, Sir William Thomson's. A static accumulating influence machine contained in Thomson's quadrant electrometer and used to change the quadrants. The cut shows the horizontal section and construction of the apparatus.

It contains two gilt brass inductors A B, and two eccentric sectors or carriers, C, D, which are mounted on an ebonite spindle, which is spun around by the fingers. The springs s s1 connect each with its inductor; the springs S S1 connect only each other, and touch the sectors as they turn around.

One of the inductors may be always assumed to be of slightly higher potential than that of the other one. When the carriers are in contact with the springs S S1 they are each charged by induction with electricity opposite in sign to that of the nearest quadrant. As they leave the springs S S1 in their rotation, they next touch the springs s s1, but of the recently opposite inductor. They share each a portion of its charge with the inductors building up their charges. The action is repeated over and over again as they rotate.

Fig. 290. THOMSON'S REPLENISHER.

460 STANDARD ELECTRICAL DICTIONARY.

Reservoir, Common. A term applied to the earth, because all electrified bodies discharge into it if connected thereto.

Fig. 289. DIAGRAM OF THOMSON'S REPLENISHER.

Residual Atmosphere. The air left in a receiver after exhaustion by an air pump. The quantity, where good air pumps are used, is very minute.

Residue, Electric. The residual charge of a condenser. (See Charge, Residual.)

Resin. (a) The product obtained by non-destructive distillation of the juice of the pitch pine. It is the solid residue left after the turpentine has been evaporated or distilled. It is a mixture of abietic acid C44 H64 O5 and pinic acid C20 H30 O2. It is an insulator; its specific inductive capacity is 2.55. (Baltzmann.)

Synonyms--Colophony--Rosin.

(b) The name is also generally applied to similar substances obtained from the sap of other trees; thus shellac is a resin. The resins are a family of vegetable products; the solid portions of the sap of certain trees. Common resin, lac, dragons blood, are examples. They are all dielectrics and sources of resinous or negative electricity when rubbed with cotton, flannel, or silk. (See Electrostatic Series.)

461 STANDARD ELECTRICAL DICTIONARY.

Resinous Electricity. Negative electricity; the electricity produced upon the surface of a resinous body by rubbing it; such a body is shellac or sealing wax; flannel and other substances may be used as the rubbing material. (See Electrostatic Series.)

Resistance. (a) The quality of an electric conductor, in virtue of which it opposes the passage of an electric current, causing the disappearance of electro-motive force if a current passes through it, and converting electric energy into heat energy in the passage of a current through it. If a current passes through a conductor of uniform resistance there is a uniform fall of potential all along its length. If of uneven resistance the fall in potential varies with the resistance. (See Potential, Fall of.)

The fall of potential is thus expressed by Daniell. "In a conductor, say a wire, along which a current is steadily and uniformly passing, there is no internal accumulation of electricity, no density of internal distribution; there is, on the other hand, an unequally distributed charge of electricity on the surface of the wire, which results in a potential diminishing within the wire from one end of the wire to the other."

Resistance varies inversely with the cross section of a cylindrical or prismatic conductor, in general with the average cross-section of any conductor, and in the same sense directly with its true or average or virtual length. It varies for different substances, and for different conditions as of temperature and pressure for the same substance. A rise of temperature in metals increases the resistance, in some bad conductors a rise of temperature decreases the resistance.

462 STANDARD ELECTRICAL DICTIONARY.

Approximately, with the exception of iron and mercury, the resistance of a metallic conductor varies with the absolute temperature. This is very roughly approximate.

Except for resistance energy would not be expended in maintaining a current through a circuit. The resistance of a conductor may be supposed to have its seat and cause in the jumps from molecule to molecule, which the current has to take in going through it. If so a current confined to a molecule would, if once started, persist because there would be no resistance in a molecule. Hence on this theory the Ampérian currents (see Magnetism, Ampere's Theory of) would require no energy for their maintenance and Ampére's theory would become a possible truth.

When metals melt their resistance suddenly increases.

Light rays falling on some substances, notably selenium, q. v., vary the resistance.

Longitudinal stretching of a conductor decreases it, it increases with longitudinal compression, and increases in iron and diminishes in tin and zinc when a transverse stress tends to widen the conductor.

(b) The term resistance is used to express any object or conductor used in circuit to develop resistance.

[Transcriber's note: At room temperatures, the thermal motion of ions in the conductor's crystal lattice scatters the electrons of the current. Imperfections of the lattice contribute slightly. At low temperatures superconductivity (zero resistance) can occur because an energy gap between the electrons and the crystal lattice prevents any interaction. At the time of this book, none of this was known. "Jumps from molecule to molecule" is a good guess.]

Resistance, Apparent. Impedance; the virtual resistance of a circuit including the spurious resistance due to counter-electromotive force. It may be made up of true resistance and partly of an inductive reaction, as it represents the net factor, the entire obstruction to the passage of a current, and not merely a superadded resistance or counter-electro-motive force.

Synonym--Impedance.

[Transcriber's note: Impedance can also have a component due to capacitance.]

Resistance, Asymmetrical. Resistance which varies in amount in different directions through a conductor. It implies a compound or composite conductor such as the human system. The presence of counter-electro-motive force in different parts of a conductor may bring about asymmetrical resistance.

Resistance, B. A. Unit of. The British Association Ohm. (See Ohm, B. A.)

463 STANDARD ELECTRICAL DICTIONARY.

Resistance Box. A box filled with resistance coils. The coils are connected in series so that a circuit including any given number has their aggregate resistance added to its own. The terminals of consecutive coils are connected to short blocks of brass which are secured to the top of the box, lying flatwise upon it, nearly but not quite in contact with each other. Plugs of brass are supplied which can go in between pairs of blocks, which have a pair of grooves reamed out to receive them. Such plugs short circuit the coil below them when in position. The cut shows how such coils are connected and the use of plugs to short circuit them. The diagram shows the top of a Wheatstone bridge, q. v., resistance box with connections for determining resistances.

Fig. 291. RESISTANCE BOX.

Resistance Box, Sliding. A resistance box whose coils are set in a circle. Two metal arms with handles are pivoted at the centre of the circle and by moving them around they make and break contacts so as to throw the coils in and out of circuit. The object is to permit an operator to adjust resistance without looking at the box--an essential in duplex telegraphy.

Resistance, Breguet Unit of. The same in origin as the Digney Unit. (See Resistance, Digney Unit of.)

It is equal to 9.652 Legal Ohms.

Resistance, Carbon. A resistance, a substitute for a resistance coil; it is made of carbon, and is of various construction. In the Brush dynamo regulator a set of four vertical piles of plates of retort carbon, q. v., is used as a resistance, whose resistance is made to vary by changing the pressure. This pressure automatically increases as the current strength increases, thus reducing the resistance.

464 STANDARD ELECTRICAL DICTIONARY.

Resistance Coil, Standard. A standard or resistance issued by the Electric Standard Committee of Great Britain. The cut shows the standard ohm. It is formed either of German silver, or of an alloy of silver, 66.6 per cent. and platinum, 33.4 per cent. The wire is insulated and doubled before winding as described before. (See Coil, Resistance.) The two ends of the wire are soldered, each one to a heavy copper wire or rod r. The whole coil is enclosed in a brass case, and is enclosed with paraffine melted in at A. A place for a thermometer is provided at t. By immersing the lower part of the case B in water of different degrees of heat any desired temperature can be attained.

Fig. 292. STANDARD OHM COIL.

Resistance, Combined. The actual resistance of several parallel conductors starting from the same point and ending at the same point. If the individual resistance be a b c d .. and the combined resistance be x then we have x = 1 / (( 1/a) + (1/b) + (1/c) + (1/d) + …)

Synonym--Joint Resistance.

Resistance, Critical. In a series wound dynamo the resistance of the outer circuit above which the machine will refuse to excite itself.

Resistance, Dielectric. The mechanical resistance of a dielectric to the tendency to perforation or to the strains due to electrification. This is a phase of mechanical resistance, and is distinct from the electrical or ohmic resistance of the same substance.

Resistance, Digney Unit of. The resistance of an iron wire, 1 kilometer long, 4 millimeters diameter, temperature unknown.

It is equal to 9.163 legal ohms.

Resistance, Electrolytic. The resistance of an electrolyte to the passage of a current decomposing it. It is almost entirely due to electrolysis and is added to by counter- electro-motive force, yet it is not treated specifically as such, but as an actual resistance. When a current of a circuit of too low voltage to decompose an electrolyte is caused by way of immersed terminals to pass through an electrolyte the resistance appears very high and sometimes almost infinite. If the voltage is increased until the electrolyte is decomposed the resistance suddenly drops, and what should be termed electrolytic resistance, far lower than the true resistance, appears.

465 STANDARD ELECTRICAL DICTIONARY.

Resistance, English Absolute or Foot-Second Unit of. A unit based on the foot and second. It is equal to (( foot / second ) * 1E7) , being based on these dimensions.

It is equal to 0.30140 legal ohm.

Resistance, Equivalent. A resistance equivalent to other resistances, which may include counter-electro-motive force.

Resistance, Essential. The resistance of the generator in an electric circuit; the same as internal resistance.

Resistance, External. In an electric circuit the resistance of the circuit outside of the generator, or battery.

Synonym--Non-essential Resistance.

Fig. 293. RESISTANCE FRAME.

Resistance Frame. An open frame filled with resistance coils of iron, or German silver wire. It is used as a resistance for dynamos and the larger or working class of plant. The coils are sometimes connected so that by a switch moving over a row of studs one or more can be thrown into series according to the stud the switch is in contact with.

Resistance, German Mile Unit of. The resistance of 8,238 yards of iron wire 1/6 inch in diameter. It is equal to 56.81 legal ohms.

466 STANDARD ELECTRICAL DICTIONARY.

Resistance, Hittorf's. A high resistance, often a megohm, composed of Hittorf's solution, q. v. It is contained in a vertical glass tube near whose upper and lower ends are electrodes of metallic cadmium attached to platinum wires. The cadmium is melted in glass tubes, the platinum wire is inserted into the melted metal and the tube is broken after all is solid. The resistance should show no polarization current.

Fig. 294. HITTORF'S RESISTANCE

Resistance, Inductive. A resistance in which self-induction is present; such as a coil of insulated wire wound around an iron core.

Resistance, Insulation. The resistance of the insulation of an insulated conductor. It is stated in ohms per mile. It is determined by immersing a section of the line in water and measuring the resistance between its conductor and the water. The section must be of known length, and its ends must both be above the liquid.

Resistance, Internal. The resistance of a battery, or generator in an electric circuit as distinguished from the resistance of the rest of the circuit, or the external resistance.

Synonym--Essential Resistance.

Resistance, Jacobi's Unit of. The resistance of a certain copper wire 25 feet long and weighing 345 grains.

It is equal to 0.6296 legal ohm.

Resistance, Matthiessen's Meter-gram Standard. The resistance of a pure hard drawn copper wire of such diameter that one meter of it weighs one gram. It is equal to .1434 Legal Ohms at 0º C. (32º F.)

Resistance, Matthiessen's Unit of. The resistance of a standard mile of pure annealed copper wire 1/16 inch diameter, at a temperature of 15.5º C. (60º F.).

It is equal to 13.44 legal ohms.

467 STANDARD ELECTRICAL DICTIONARY.

Resistance, Meter-millimeter Unit of. The resistance of a wire of copper one meter long and one square millimeter in section. It is equal to .02057 ohms at 0º C. (32º F.) The term may also be applied to the resistance of similar sized wire of other metals.

Resistance, Mil-foot Unit of. The resistance of a foot of copper wire one-thousandth of an inch in diameter. It is equal to 9.831 ohms at 0º C. (32º F.) The term may also be applied to the resistance of similar sized wire of other metals.

Resistance, Non-essential. The resistance of the portion of an electric circuit not within the generator; the same as external resistance.

Synonym--External Resistance.

Resistance, Non-inductive. A resistance with comparatively little or negligible self-induction.

Resistance of Human Body. The resistance of the human body is largely a matter of perfection of the contacts between its surface and the electrodes. It has been asserted that it is affected by disease. From 350 to 8,000 ohms have been determined as resistances, but so much depends on the contacts that little value attaches to the results.

Resistance, Ohmic. True resistance measured in ohms as distinguished from counter-electro-motive force, q. v. The latter is called often spurious resistance.

Synonym--True Resistance.

[Transcriber's note: "True" vs. "spurious" are interesting terms, considering that today we define impedance as a combination of "real" resistance and "imaginary" capacitive and inductive reactance.]

Resistance, Reduced. The resistance of a conductor reduced to ohms, or to equivalent lengths of a column of mercury, 1 square millimeter in cross area.

Resistance, Siemen's Unit of. The resistance of a column of mercury 1 meter long and 1 square millimeter cross-sectional area at 0º C. (32º F.)

It is equal to .9431 legal ohm.

Resistance, Specific. The relative resistance of a substance. It is expressed as the actual resistance of a cube of the substance which is one centimeter on each edge. For metals it is usually expressed in microhms, for liquids in ohms.

The resistances of a specified length of wire of specified diameter of different substances is often given, and is really a particular way of stating specific resistances.

Synonym--Specific Conduction Resistance.

Resistance, Spurious. The counter-electro-motive force, q. v., operating to prevent a current being produced of what should be its full strength were the true resistance and actuating electro-motive force only concerned. Such counter-electro-motive force may be treated as a spurious resistance and such a value in ohms assigned to it as would correspond to its proper effect.

468 STANDARD ELECTRICAL DICTIONARY.

In its effect on opposing a current and in resisting its formation it differs from true resistance. The latter in diminishing current strength absorbs energy and develops heat; spurious resistance opposes and diminishes a current without absorption of energy or production of heat.

[Transcriber's note: "Spurious resistance" is now called reactance, consisting of capacitive reactance and inductive reactance. The combination of reactance and (Ohmic/true) resistance is called impedance. The calculation of impedance requires complex algebra, not just real values used in DC circuit analysis.]

Resistance, Steadying. When arc lamps are connected in parallel or multiple arc a small resistance coil is sometimes placed in series with each lamp for steadying purposes. It reduces the percentage of variation of resistance in each lamp, which may be caused by a change in the position of the carbons.

Resistance, Swiss Unit of. A unit constructed by the "Administration Suisse," based on the same data as the Breguet and the Digney Units. (See Resistance, Digney Unit of)

It is equal to 10.30 legal ohms.

Resistance, Thomson's Unit of. A unit of resistance based on the foot and second.

It is equal to 0.3166 legal ohm.

Resistance, Unit. Unit resistance is that of a conductor in which unit current is produced by unit electro-motive force.

Resistance, Varley's Unit of. The resistance of a standard mile of a special copper wire 1/16 inch diameter.

It is equal to 25.33 ohms.

Resistance, Weber's Absolute Unit. A metric system unit; (meter / second) * 1E7

It is equal to 0.9089 legal ohm.

Resonance, Electric. A set of phenomena known as the Hertz experiments are grouped under this title, which phenomena are incidents of and depend on the propagation of electric waves through wires or current conductors, as well as through the ether. Ordinarily a wire is only a seat of current, and is in its nature inconsistent with wave propagation through its mass. Such waves are virtually confined to the exterior of the wire. The point is that the current-producing force is supposed to enter the wire at all points from without, the current not being produced by an end-push. Hence in rapidly recurring waves which are produced by a rapidly pulsatory or alternating current, no time is afforded for the current-producing force, in this case the wave-producing force, to penetrate into the substance of the wire. In one of his experiments Dr. Hertz surrounded a wire by a glass tube chemically silvered. The coating was so thin as to be translucent. Through this metallic layer a current could be induced in the wire in its interior. Any mechanical layer of metal took up the induction itself, and protected the central wire. This gave a clue to the thickness of metal penetrated by the rapid induced waves used by Dr. Hertz.

469 STANDARD ELECTRICAL DICTIONARY.

Fig. 295. ELECTRICAL RESONANCE EXCITER.

The method used for the production of rapid oscillations is the following. To the terminals of an induction coil two metal spheres AA1 are connected as shown. This apparatus is termed the exciter; in its discharge a series of isochronous discharges takes place, alternating in direction. The period of duration T of a single one is given by the formula T= 2* PI * squareRoot( LC ), in which C is the capacity and L is the self-induction. The spheres may be 30 centimeters (11.8 inches) in diameter, connected each to conductors 0.5 centimeter (.2 inch) in diameter and 40 centimeters (15.7 inches) long each. For the length of an undulation the formula gives for this apparatus 4.8 meters (15.75 feet) as the length of a wave, assuming for them the velocity of propagation equal to that of light. The exciter may have 10,000 times the rate of oscillation possessed by the plain induction coil.

When this apparatus is worked it produces induced waves in every neighboring conductor. The resonance effects appear in the size of the spark induced. Thus a wire bent into a circle with its ends nearly touching will give a spark, but if made of proper electrostatic capacity, corresponding with the particular waves employed, the spark will be very much larger. The ring, with its spark gap is termed a resonator. It is used as an explorer to trace the waves.

Waves thus produced are transmitted by stone walls and nonconductors in general. A plate of zinc reflects part and transmits part. The reflected waves can be traced by the resonator, their angle of reflection being equal to their angle of incidence. They can be received by one parabolic reflector, reflected to another and brought to a focus. They can be reflected so as to produce interference or loops and nodes, and the loops and nodes can be traced by the resonator. By a prism of asphalt they are refracted exactly like light.

From all this it is concluded that an additional proof is furnished of the identity of light and electro-magnetic waves, and a very strong experimental proof of Maxwell's theory of light is furnished.

Synonym--Hertz's Experiments.

470 STANDARD ELECTRICAL DICTIONARY.

Fig. 296. ELECTRICAL RESONATOR.

Resonator, Electric. A small open electric circuit, with ends nearly touching. When exposed to electric resonance, or to a sympathetic electric oscillatory discharge, a spark passes from across the gap. The production of this spark is altogether a matter of the inductance of the resonator. The simplest form is a circle of copper wire with its ends nearly touching. The length of the gap is adjustable by bending. A screw adjustment may also be provided. Another form is shown in the cut, Fig. 296. Here sheets of tinfoil are used to regulate the electrostatic capacity, while at m is shown the finger piece for regulating the size of the spark gap a.

Synonym--Spark Micrometer.

Resultant. The line indicating the result of the application of two or more forces to a point. Its direction and length give the elements of direction and intensity. (See Forces, Resolution of Forces, Composition of Components.)

Resultant Polarity. The magnetic polarity imparted to a mass of iron acted on by two or more separate inducing forces or currents. It appears in dynamos and motors. The final polarity is the resultant of the inducing effect of the field magnet poles and of the windings.

Retardation. In telegraphy a retardation of the rate of transmission of signals. It is due to several causes.

(a) The self-induction of the circuit, especially if it includes many electro-magnets, produces extra currents (see Currents, Extra.) These are opposed to the main current on closing it and hence retard the action. They are in the same direction on opening it and hence again retard the action.

(b) Every line has a certain static capacity. This is affected by the proximity of the lines to the earth. For each signal electricity has to be charged upon the line until the line is charged to its end with a certain proportion of the initial density. This charging takes time and hence introduces retardation.

(c) The cores of the electro-magnets of the relays or sounders are not instantly magnetized and demagnetized. This magnetic lag, q. v., introduces retardation.

471 STANDARD ELECTRICAL DICTIONARY.

Retardation of Phase. The fractional lagging behind of waves or alternating currents; by lagging behind a portion of a wave length the corresponding phases, as of full amplitude, are kept back or retarded. The phase of current intensity may be retarded with reference to the electro-motive force by the introduction of transformers of high capacity with high resistance on open secondary circuits.

[Transcriber's note: Capacitors are used to correct current phase lag.]

Retentivity. Coercitive or coercive force; by virtue of which steel retains its magnetism. It is the more modern name, "coercive force" as a term being rejected by many.

Synonyms--Coercive Force--Coercitive Force.

Retort Carbon. Carbon deposited in coal gas retorts from decomposition of the hydrocarbons. It is a very hard, pure form, and is of graphitic modification. Owing to its great hardness it is little used for electrical purposes, the molded carbons being easier to make. The deposition occurs in the regular gas-making process, and is a disadvantage to the working.

Return. A line or conductor which is supposed to carry current back to its starting point, after it has traversed a line. It may be a wire or the grounding of the ends of a line [or] may make the earth act as a return, termed ground- or earth-return. The best distinction of a return is to so term the portion of a circuit on which no apparatus is placed.

Reversibility. The principal in virtue of which a device for producing a given form of energy can absorb the same and do work. The reversibility of the dynamo is its quality in virtue of which it can act as a current generator, thereby converting mechanical energy into electric energy, or if a current is passed through it, it rotates, doing work, and thereby converting electric energy into mechanical energy. The knowledge of this principle can be traced back to Jacobi in 1850.

Reversible Bridge. A form of Wheatstone's Bridge adapted for reversal of the positions or interchange of the proportionate arms, v., so that the accuracy of the coils can be tested.

Rheochord. An apparatus by means of which variable quantities of wire are thrown into the circuit; a rheostat using wire. (See Rheostat, Wheatstone's.)

Rheometer. A galvanometer. (Obsolete.)

472 STANDARD ELECTRICAL DICTIONARY.

Rheomotor. A source of current; a current generator; a producer of potential difference. (Obsolete.)

Rheophore. The portion of an active circuit capable of deflecting a magnetic needle. This properly includes all of the metallic conductor of a circuit. (Obsolete.)

Rheoscope. A galvanoscope; an instrument for qualitatively detecting potential difference, fall or rise. (See Galvanoscope.)

Rheostat. An adjustable resistance; an apparatus for changing the resistance without opening the circuit. Its action may depend on the introduction of variable lengths of mercury column, of some other liquid, or of wire into a circuit. (See Rheostat, Wheatstone's.)

Rheostat Arm. The third arm of known resistance in a Wheatstone bridge. (See Proportionate Arms.)

Rheostatic Machine. An apparatus for increasing potential difference. It consists of a number of static condensers. They are charged in multiple arc or in parallel, and are discharged in series. Secondary batteries may be used for the charging; thus a static effect is produced from a galvanic battery.

Rheostat, Wheatstone's. This apparatus consists of two cylinders, one, A, made of brass, the other, B, of wood, with a spiral groove. At its end is a copper ring a. A fine brass wire has one end attached to this ring. Its other end is fastened at e, and it is wound as shown; n and o are binding screws connected, one with the cylinder-ring a, the other with the brass cylinder, A. The current entering at o, traverses the wire on B, as there the windings are insulated by the grooves, thence it passes to m and by A, whose metal short circuits all the wire on it, to the binding-post n. The handle, d, is turned one way or the other to regulate the length of the wire through which the current must pass. On each cylinder there is a square head, one of which is shown at c, so that the handle can be shifted from one to the other as required; to A if the wire is to be wound on that cylinder, to B if the reverse is desired.

Fig. 297. WHEATSTONE'S RHEOSTAT.

473 STANDARD ELECTRICAL DICTIONARY.

Rheotome. An automatic circuit breaker, one which rapidly opens and closes a circuit, as in the case of the primary of an induction coil an interrupter. (Obsolete.)

Rheotrope. A pole changer, current reverser, or commutator, g., such as the commutator of an induction coil. (Obsolete.)

Rhigolene. A petroleum product; a hydrocarbon of low boiling point. Its vapor is used in flashing (q. v.) carbon filaments for incandescent lamps.

Rhumbs. In a mariners' compass, the thirty-two points, designated, north, north by east, north north east, etc. (See Compass Mariner's-Compass, Points of the.)

Rhumkorff Coil. The induction coil, q. v.

Rigidity, Molecular. The tendency of molecules to resist rotation or change of position; the assumed cause of magnetic coercive force, or retentivity.

Ring Contact. A contact formed by a terminal clip in the shape of a ring, split or cut at one point so that its ends tend to spring together. The other terminal is a bar which passes into the cut and is tightly pressed by the elastic ring.

Fig. 298. SWITCH WITH RING CONTACTS.

474 STANDARD ELECTRICAL DICTIONARY.

Ring, Faraday. A closed ring of iron used as the core of a transformer or induction coil. The term is derived from Faraday's classic experiment with such an apparatus when he produced a spark by induction in a secondary circuit.

Roaring. A term applied to the noise sometimes produced in a voltaic arc, when the electrodes are close together and a heavy current is passing.

Rocker. In a dynamo the movable piece, mounted concentrically with the commutator, and carrying the rocker-arms and brush-holders. By moving it the brushes are adjusted for proper lead.

Rocker Arms. The arms projecting from a rocker and each carrying one of the brush-holders.

Roget's Spiral. An experimental apparatus for illustrating the mutual attraction of currents going in like direction. A cylindrical helix or spiral of wire is suspended by one end. Its lower end just dips into a mercury cup. An active circuit is connected, one terminal to the upper end, the other terminal to the mercury cup, bringing the apparatus in series into the circuit. The current as it passes causes the coil to shorten, each spiral attracting its neighbors. This breaks the circuit by drawing the lower end out of the mercury cup. The current being cut off the coils cease to attract each other, and the end dips into the mercury cup again. This closes the circuit, the coils again attract each other and the same sequence follows and is repeated over and over again. A bright spark is produced at each break of the mercury contact.

Rotation of Liquids, Electro-dynamic. By passing a current through a liquid, such as dilute sulphuric acid, it rotates if exposed to the induction of a current flowing at right angles to it. The condition resolves itself into a liquid traversed by horizontal currents from centre to circumference or vice versa, rotated by a current passing through a circular conductor below it.

475 STANDARD ELECTRICAL DICTIONARY.

Rotation of Liquids, Electro-magnetic. The rotation produced in a liquid carrying centripetal or centrifugal currents by an electromagnet. It is practically an intensification of electro-dynamic rotation. (See Rotation of Liquids, Electro-dynamic.)

Rubber. In a frictional electric machine the cushion of leather which is pressed against the plate as it rotates.

S. (a) Symbol for second.

(b) Symbol for space, or length; L is preferable.

(c) Symbol for south-seeking pole of a magnet.

Saddle Bracket. A bracket carried on the top of telegraph poles, carrying an insulator for the upper wire.

Safety Device. (a) A device to prevent overheating of any portion of a circuit by excess of current. It generally consists of a slip of fusible metal which if the current attains too much strength melts and opens the circuit. To ensure its breaking a weight is sometimes suspended from the strip. In one form an insulated German silver wire is wrapped around the end of the fusible strip a number of times and its end is connected to it. The other end of the German silver wire connects with the main lead, so that all the current goes through both in series. If the German silver wire becomes heated from excess of current the coil wrapped tightly around the end of the fusible strip melts it and opens the circuit.

(b) Lightning arresters, q. v., may be cited under this heading.

Synonyms--Automatic Cut Out--Safety Fuse, Plug, or Strip.

Fig. 299. COCKBURN SAFETY FUSE.

Safety Fuse. A strip of metal inserted so as to form part of a circuit and of such size that a smaller current [than] would heat the regular wire of the circuit dangerously, so as to cause a conflagration for instance, would melt the fuse and open the circuit. As it sometimes happens that a safety fuse melts without parting a weight is sometimes hung upon it, so as to break it as it softens.

Salt. A salt is a chemical compound containing two atoms of two radicals,. which saturate each other. One atom or radical is electro-positive referred to the other, which is electro-negative. By electrolysis salts are decomposed, the atoms or radicals separating and uniting to form new molecules.

476 STANDARD ELECTRICAL DICTIONARY.

Saturated. adj. A liquid is saturated with a substance when it has dissolved all that it can, while an excess is present in the liquid. It is possible, by dissolving some salts in hot water and allowing the solution to cool without access of air, to obtain a supersaturated solution. On introduction of a crystal of the salt, or often on mere access of air, the solution forms crystals and the liquid left is saturated.

Saw, Electric. A platinum coated steel wire mounted and connected to be raised to incandescence for cutting purposes.

Schweigger's Multiplier. An old term for the galvanometer as invented by Schweigger soon after Oerstedt's discovery.

Scratch Brushes. Brushes for cleaning the surface of articles to be electroplated to give a good metallic surface suitable for deposition. They have often wire instead of bristles.

477 STANDARD ELECTRICAL DICTIONARY.

Fig. 300. WIRE GAUZE ELECTRIC SCREEN.

Screen, Electric. A large plate or a hollow case or cage of conducting material connected with the earth, and used to protect any body placed within it from electrostatic influences.

If within a hollow conducting sphere an electrified body is placed, the inner surface of the sphere will be charged with electricity of opposite kind to that of the sphere, and the outer surface with the same kind as that of the sphere. Thus the sum of the electricities called into action by induction is zero. The two inner charges are bound to each other. The induced charge on the outer surface of the sphere is all that has any effect on objects in the outer air.

If the outer surface is connected to the earth it becomes discharged, and however highly electrified the body introduced into the sphere and the inner surface of such sphere may be, they produce no external effects, as they are bound one to the other.

If the sphere is connected to the earth and an unelectrified object is placed within it, such object will be perfectly shielded from the effects of an outer electrostatic field. Perforated tinfoil or wire gauze has just as good a result. A large plate of metal connected to the earth has the same effect. The screen whether plane or hollow simply retains a bound charge due to the field of force, thereby neutralizing it, and the electricity of the opposite sign escapes to the earth. Thus a true shielding or screening effect is produced.

In the cut an experiment is shown in which an electric screen is carried by a Leyden jar. Pith balls are suspended outside and inside of it. By the approach of an electrified body the outer pith balls will diverge, while no effect is produced upon the inner ones.

Secondary Actions. In electrolysis the direct products of the electrical decomposition are not always obtained at the electrodes, but products due to their reaction on the water and other chemicals may appear. These constitute secondary actions. Thus if a solution of copper sulphate is electrolyzed with platinum electrodes, metallic copper appears at one pole and sulphuric acid and oxygen gas at the other. But the products of electrolysis by the current are copper (Cu) and sulphion (SO4). The latter reacting on water sets free oxygen gas and forms sulphuric acid. The latter is a secondary action.

Secondary Generator. (a) An alternating current converter generating a so-called secondary current.

(b) A secondary battery, q. v., may be thus termed.

Secondary, Movable. The term movable secondaries has been applied to rings, spheres and discs of conducting material, such as copper, whose behavior when near the pole of an electro-magnet traversed by an alternating current, have been studied by Elihu Thomson. Such masses are subjected to very peculiar movements and mutual reactions. As the phenomena are due to induced currents the above term has been applied to the masses in which the currents are induced.

478 STANDARD ELECTRICAL DICTIONARY.

Secondary Plates, Colors of. In a secondary battery of the lead plate type, the color of the plates is a good indication of the condition of the battery. The negative plate should be brown or deep-reddish, the other should be slate-colored.

Secondary Poles. Poles sometimes found in magnets existing in positions intermediate between the end or true poles.

Synonym--Consequent Poles.

Seebeck Effect. The production of a current by heating the junction of two different metals forming part of a circuit, or the thermo-electric production of current, is stated as the Seebeck effect, having been discovered by that investigator.

Selenium. A non-metallic element. It is interesting electrically on account of the changes its electric resistance undergoes when it is subjected to light.

In one set of experiments it was found that diffused light caused the resistance to fall in the ratio of 11 to 9. Full sunlight reduced it to one-half. Of the spectrum colors red was most powerful and the ultra red region still more strongly affected its resistance.

The effect produced by exposure to light is instantaneous, but on removal to the dark only slowly disappears.

A vessel of hot water was found to have no effect, showing that short ether waves are essential to the effect.

Selenium Cell. A selenium resistance box. Vitreous selenium is made by keeping ordinary selenium for some hours at a temperature of about 220º C. (428º F.) after fusing. It is placed in an electric circuit as part of the conductor.

Its resistance can then be determined. It decreases in sunlight to about one-half its resistance in the dark.

The selenium cell is used in the Photophone, q. v. Otherwise it is little more than a subject of experiment.

Selenium Eye. A model eye in which selenium in circuit with a battery and galvanometer takes the place of the retina of the human eye.

Self-repulsion. When a body is electrified each molecule repels its neighbor and the condition in question is thus designated. An electrified soap-bubble expands in virtue of self-repulsion.

Semi-conductors. Substances which conduct static electricity poorly, but quite appreciably and beyond the extent of leakage. The following are examples: Alcohol and ether, powdered glass, flowers of sulphur, dry wood, paper, ice at 0º C. (32º F.)

479 STANDARD ELECTRICAL DICTIONARY.

Sensibility. The measure of the effect of a current upon a galvanometer, or any similar case.

Sensitiveness, Angle of Maximum. Every galvanometer has its angle of maximum sensitiveness, which is the angle of deflection at which a small increment of current will produce the greatest deflection. For every tangent galvanometer 45° is the angle in question. In using a galvanometer for direct reading methods it is an object to have it work at its angle of maximum sensitiveness.

Separately Excited Dynamo. A dynamo-electric machine whose field magnet is excited from an outside source, which may be another dynamo or a battery. Alternating current dynamos are often of this description.

Separate Touch. In magnetism a method of inducing magnetism in a steel bar. The opposite poles of two magnets are applied at the center of the bar to be magnetized, but without touching each other, and are drawn apart to its ends. They are returned through the air and the process is repeated a number of times and on both sides of the bar if necessary.

Separation of Electricities. Under the double fluid theory of electricity the action of electrification in accumulating positive electricity in one conductor and negative on the other of the excited surfaces of two conductors.

Separator. India rubber bands or other forms used in batteries to keep the plates from touching in the cell; especially applied to secondary batteries, where the plates are so near together as to require separators to prevent short circuiting.

Fig. 301. SERIES CONNECTION.

Series. (a) Arranged in succession as opposed to parallel. Thus if a set of battery jars are arranged with the zinc of one connected to the carbon of the next one for the entire number, it is said to be arranged in series. When incandescent lamps are arranged in succession so that the current goes through one after the other they are arranged in series.

The opposite of parallel, q. v., or multiple arc, q. v.; it may be used as a noun or as an adjective.

(b) See Electro-Chemical Series;

(c) Thermo-Electric Series

(d) Electrostatic Series;

(e) Electro-motive Series.

Synonym--Cascade Connection (but little used.)

480 STANDARD ELECTRICAL DICTIONARY.

Series-multiple. Arrangement of electric apparatus, in which the parts are grouped in sets in parallel and these sets are connected in series. It is used as a noun, as "arranged in series-multiple," or as an adjective, as "a series-multiple circuit or system."

Fig. 302. SERIES-MULTIPLE CONNECTION.

Service Conductors. In electric distribution the equivalents of service pipes in the distribution of gas; wires leading from the street mains to the houses, where current is to be supplied.

Serving. The wrapping or winding of a cable composed of small size wire, laid closely and smoothly with a tool called a serving mallet, or serving block, or by machinery. It serves to protect the cable from wear.

Shackle. In telegraph lines a swinging insulator bracket for use where wires make an angle with the pole. A journal box is attached to the pole, like half of a gate hinge. To this a short iron arm is pivoted so as to be free to swing through a considerable angle. At its end an insulator is carried to which the wire is attached. The shackle swings into line with the wire, or takes a position for two wires corresponding to the resultant of their directions of pull.

Fig. 303. DOUBLE SHACKLE

Shadow. Electric. A term applied to a phenomenon of high vacua. If an electric discharge is maintained in a Crookes' tube the glass opposite the negative electrode tends to phosphoresce. A plate of aluminum, used also as the positive electrode, protects the glass directly behind it so as to produce the effect of a shadow.

Synonym--Molecular Shadow.

[Transcriber's note: The effect is due to the "shadowing" of the electrons streaming past the plate.]

481 STANDARD ELECTRICAL DICTIONARY.

Sheath for Magnet Coils. In 1867 C. E. Varley proposed the use of a copper sheath surrounding a magnet core to diminish self-induction. It has since been used by Brush and others. Sometimes metallic foil is laid between the successive coils of wire.

Synonym--Mutual Induction Protector.

Sheath for Transformers. A protective sheath of copper, interposed between the primary and secondary circuits of an alternating current transformer. It is connected to the earth. If the primary coil loses its insulation before it can leak to the secondary it is grounded. This protects the secondary circuit from the high electro-motive force of the primary circuit.

Shellac. A resin; produced as an exudation upon the branches of certain Asiatic trees, such as the banyan (Ficus religiosa). It is due to punctures in the bark of the trees in question, which punctures are made by the female of the insect coccus ficus or c. lacca.

Commercial shellac contains about 90 per cent. of resinous material, the rest is made up of wax, gluten, coloring matter and other substances.

Shellac is soluble in alcohol, and in aqueous solutions of ammonium chloride, of borax and in strong ammonia solution. Long standing is required in the case of the last named solvent. Dilute hydrochloric and acetic acids dissolve it readily; nitric acid slowly; strong sulphuric acid is without action on it. Alkalies dissolve it.

In electric work it is used as an insulator and dielectric. Its alcoholic solution is used to varnish glass plates of influence machines, for the coils of induction coils and similar purposes.

Resistance in ohms per centimeter cube at 28° C. (82.4 F.)--(Ayrton), 9.0E15

Specific Inductive Capacity (Wüllner), 2.95 to 3.73

The same substance in less pure forms occurs in commerce, as stick lac, lump lac, seed lac, button lac.

Shellac Varnish. Solution of shellac in alcohol; methylic alcohol (wood alcohol or wood naphtha) is often used as solvent.

Dr. Muirhead recommends button lac, dissolved in absolute alcohol, and the top layers decanted. For highest insulation he dissolves the lac in ordinary alcohol, precipitates by dropping into water, collects the precipitate, dries and dissolves in absolute alcohol.

Shielded. adj. An electric measuring instrument of the galvanometer type is shielded when it is so constructed that its indications are not seriously affected by the presence of neighboring magnets or by fields of force. Shielding can be effected by using a very strong permanent magnet to produce a field within which the magnetic needle moves and which reacts upon it, or by enclosing the instrument in a thick iron box.

482 STANDARD ELECTRICAL DICTIONARY.

S. H. M. Symbol or abbreviation for "simple harmonic motion."

Shock, Break. A term in electro-therapeutics; the shock received when an electric circuit, including the patient in series, is broken or opened.

Synonym--Opening Shock.

Shock, Electric. The effect upon the animal system of the discharge through it of electricity with high potential difference. Pain, nervous shock, violent muscular contortions accompany it. Of currents, an alternating current is reputed worse than a direct current; intermediate is the pulsatory current.

The voltage is the main element of shock, amperage has also some direct influence.

Shock, Static. A term in electro-therapeutics. The application of static discharges from small condensers or Leyden jars to a patient who is insulated from the ground with one electrode applied to the conducting surface on which he rests, while the other, a spherical electrode, is brought near the body so as to produce a disruptive or spark discharge.

Short Circuit. A connection between two parts of a circuit, which connection is of low resistance compared to the intercepted portion. The term is used also as a verb, as "to short circuit a lamp."

Fig. 304. DIAGRAM ILLUSTRATING SHORT CIRCUIT WORKING.

Short Circuit Working. A method of working intermittently an electro-magnet so as to avoid sparking. It consists in providing a short circuit in parallel with the magnetic coils. This short circuit is of very low resistance. To throw the magnet into action the short circuit is opened; to throw it out of action the short circuit is closed. The shunt or short circuit must be of negligibly small resistance and inductance.

483 STANDARD ELECTRICAL DICTIONARY.

Shovel Electrodes. Large plate electrodes used in a medical bipolar bath. (See Bath, Bipolar.)

Shunt. In a current circuit a connection in parallel with a portion of the circuit. Thus in a dynamo a special winding for the field may have its ends connected to the bushes, from which the regular external circuit also starts. The field is then wound in shunt with the armature. In the case of a galvanometer a resistance coil may be put in parallel with it to prevent too much current going through the galvanometer; this connection is a shunt.

The word is used as a noun, as "a shunt," or "a connection or apparatus in shunt with another," and as an adjective, as "a shunt connection," or as a verb, as "to shunt a battery."

Shunt Box. A resistance box designed for use as a galvanometer shunt. (See Shunt, Galvanometer.) The box contains a series of resistance coils which can be plugged in or out as required.

Shunt, Electro-magnetic. In telegraphy a shunt for the receiving relay consisting of the coils of an electro-magnet. It is placed in parallel with the relay. Its poles are permanently connected by an armature. Thus it has high self-induction.

On opening and closing the circuit by the sending key, extra currents are produced in the shunt. The connections are so arranged that on making the circuit the extra current goes through the relay in the same direction as the principal current, while on breaking the circuit the induced current goes in the opposite direction.

Thus the extra currents accelerate the production and also the cessation of signalling currents, tending to facilitate the operations of sending despatches.

Shunt, Galvanometer. A resistance placed in parallel with a galvanometer, so as to short circuit its coils and prevent enough current passing through it to injure it. By knowing the resistance of the shunt and of the galvanometer coils, the proportion of current affecting the galvanometer is known. This gives the requisite factor for calculation. (See Multiplying Power of Shunt.)

Shunt Ratio. The coefficient expressing the ratio existing between the current in a shunt and in the apparatus or conductor in parallel with it. (See Multiplying Power of/ Shunt.)

Shunt Winding. A dynamo or motor is shunt-wound when the field magnet winding is in shunt or in parallel with the winding of the armature.

Shuttle Current. A current alternating in direction; an alternating current.

484 STANDARD ELECTRICAL DICTIONARY.

Side-Flash. A bright flashing lateral discharge from a conductor conveying a current due to a static discharge.

Sighted Position. In an absolute electrometer (see Electrometer, Absolute) the position of the balanced arm carrying the movable disc or plate, when the disc and guard plate are in one plane. The cross-hair on the lever-end is then seen midway between two stops, or some other equivalent position is reached which is discerned by sighting through a magnifying glass or telescope.

Silver. A metal; one of the elements; symbol Ag.; atomic weight, 108; valency, 1; equivalent, 108; specific gravity, 10.5. It is a conductor of electricity. Relative resistance, annealed, 1.0 Specific Resistance, annealed, at 0° C. (32° F.) 1.504 microhms. Resistance of a wire at 0° C. (32° F.), Annealed. Hard Drawn. (a) 1 foot long, weighing 1 grain, .2190 ohms .2389 ohms. (b) 1 foot long, 1/1000 inch thick, 9.048 " 9.826 " (c) 1 meter long, weighing 1 gram, .1527 " .1662 " (d) 1 meter long, 1 millimeter thick, .01916 " .02080 "

Resistance annealed of a 1-inch cube, at 0° C. (32°F.) .5921 microhms.

Percentage increase in resistance per degree C. (1.8 F.) at about 20° C. (68° F.), annealed, 0.377 per cent.

Electro-chemical equivalent, (Hydrogen = .0105) .1134 mgs.

Silver Bath. A solution of a salt of silver for deposition in the electroplating process.

The following is a typical formula: Water, 10.0 parts by weight. Potassium Cyanide, 5 " " Metallic Silver, 2.5 " "

The silver is first dissolved as nitrate and converted into cyanide and added in that form, or for 2.5 parts metallic silver we may read: Silver cyanide, 3 parts by weight.

While many other formulas have been published the above is representative of the majority. Other solvents for the silver than potassium cyanide have been suggested, such as sodium hyposulphite, but the cyanide solution remains the standard.

Silver Stripping Bath. Various baths are used to remove silver from old electroplated articles. Their composition depends upon the base on which the metal is deposited. Silvered iron articles are placed as anodes in a solution of 1 part potassium cyanide in 20 parts of water. As kathode a silver anode or a copper one lightly oiled may be used. From the latter the silver easily rubs off. For copper articles a mixture of fuming sulphuric acid and nitric acid (40º Beaumé) may be used. The presence of any water in this mixture will bring about the solution of the copper. Or fuming sulphuric acid may be heated to between 300º and 400º F., some pinches of dry pulverized potassium nitrate may be thrown in and the articles at once dipped. These methods effect the solution of the silver, leaving the copper unattacked.

485 STANDARD ELECTRICAL DICTIONARY.

Simple Substitution. A method of obtaining a resistance equal to that of a standard. The standard is put in circuit with a galvanometer and the deflection is noted. For the standard another wire is substituted and its length altered until the same deflection is produced. The two resistances are then evidently identical. The standard can be again substituted to confirm the result.

Sine Curve. If we imagine a point moved back and forth synchronously with a pendulum, and if such point made a mark upon paper, it would trace the same line over and over again. If now the paper were drawn steadily along at right angles to the line of motion of the point, then the point would trace upon it a line like the profile of a wave. Such line is a sine curve. It derives its name from the following construction. Let a straight line be drawn, and laid off in fractions, such as degrees, of the perimeter of a circle of given diameter. Then on each division of the line let a perpendicular be erected equal in height to the sine of the angle of the circle corresponding to that division; then if the extremities of such lines be united by a curve such curve will be a sine curve.

In such a curve the abscissas are proportional to the times, while the ordinates are proportional to the sines of angles, which angles are themselves proportional to the times. The ordinates pass through positive and negative values alternately, while the abscissas are always positive.

Any number of sine curves can be constructed by varying the diameter of the original circle, or by giving to the abscissas a value which is a multiple of the true length of the divisions of circle. If the pendulum method of construction were used this would be attained by giving a greater or less velocity to the paper as drawn under the pendulum.

A species of equation for the curve is given as follows: y = sin( x )

In this x really indicates the arc whose length is x, and reference should be made to the value of the radius of the circle from which the curve is described. It will also be noticed that the equation only covers the case in which the true divisions of the circle are laid off on the line. If a multiple of such divisions are used, say n times, or 1-n times, then the equation should read y = n sin( x ) or y = sin( x ) / n

Synonyms--Curve of Sines--Sinusoidal Curve--Harmonic Curve.

486 STANDARD ELECTRICAL DICTIONARY.

Sine Law. The force acting on a body is directly proportional to the sine of the angle of deflection when--

I. The controlling force is constant in magnitude and direction; and

II. The deflecting force, although variable in its direction in space, is fixed in direction relatively to the deflecting body.

Single Fluid Theory. A theory of electricity. Electricity, as has been said, being conveniently treated as a fluid or fluids, the single fluid theory attributes electrical phenomena to the presence or absence of a single fluid. The fluid repels itself but attracts matter; an excess creates positive, a deficiency, negative electrification; friction, contact action or other generating cause altering the distribution creates potential difference or electrification. The assumed direction (see Direction) of the current and of lines of force are based on the single fluid theory. Like the double fluid theory, q. v., it is merely a convenience and not the expression of a truth. (See Fluid, Electric, and Double Fluid Theory.)

Synonym--Franklin's Theory.

Single Fluid Voltaic Cell. A galvanic couple using only a single fluid, such as the Smee or Volta cell.

Simple Harmonic Motion. Motion of a point or body back and forth along a line; the motion of a pendulum, as regards its successive swings back and forth, is an example of harmonic motion.

Sinistrotorsal. adj. The reverse of dextrotorsal, q. v. A helix with left-handed winding, the reverse of an ordinary screw, such as a wood-screw or corkscrew.

Skin Effect. A current of very brief duration does not penetrate the mass of a conductor. Alternating currents for this reason are mainly conducted by the outer layers of a conductor. The above is sometimes called the skin effect.

Sled. A contact for electric cars of the conduit system. It is identical with the plow, q.v., but is drawn after the cars instead of being pushed along with them.

Slide Meter Bridge. A name for a Slide Bridge one meter long. There are also slide half meter and slide quarter meter bridges and others. (See Meter Bridge.)

S. N. Code. Abbreviation for single needle code, the telegraphic alphabet used with the single needle system.

Soaking-in-and-out. A term for the phenomena of the residual electrostatic charge; the gradual acquirement or loss by a condenser of a portion of its electrostatic charge.

487 STANDARD ELECTRICAL DICTIONARY.

Soldering, Electric. (a) Soldering in which the solder is melted by means of electricity; either current incandescence or the voltaic arc may be used. It is identical in general with electric welding. (See Welding, Electric.)

(b) The deposition by electric plating of a metal over the ends of two conductors held in contact. This secures them as if by soldering. It is used in connecting the carbon filament of an incandescent lamp with the platinum wires that pass through the glass. Copper is the metal usually deposited.

Solenoid. The ideal solenoid is a system of circular currents of uniform direction, equal, parallel, of equal diameter of circle, and with their centers lying on the same straight line, which line is perpendicular to their planes.

Fig. 305. EXPERIMENTAL SOLENOID.

The simple solenoid as constructed of wire, is a helical coil, of uniform diameter, so as to represent a cylinder. After completing the coil one end of the wire is bent back and carried through the centre of the coil, bringing thus both ends out at the same end. The object of doing this is to cause this straight return member to neutralize the longitudinal component of the helical turns. This it does approximately so as to cause the solenoid for its practical action to correspond with the ideal solenoid.

Instead of carrying one end of the wire through the centre of the coil as just described, both ends may be bent back and brought together at the centre.

A solenoid should always have this neutralization of the longitudinal component of the helices provided for; otherwise it is not a true solenoid.

Solenoids are used in experiments to represent magnets and to study and illustrate their laws. When a current goes through them they acquire polarity, attract iron, develop lines of force and act in general like magnets.

A solenoid is also defined as a coil of insulated wire whose length is not small as compared with its diameter.

488 STANDARD ELECTRICAL DICTIONARY.

Sonometer, Hughes'. A sound measurer; a modification of a portion of Hughes' induction balance, used for testing the delicacy of the ear or for determining the relative intensity of sounds. (See Hughes' Induction Balance.) It is the arrangement of three coils, two mounted one at each of the ends of a graduated bar, and the third one between them and free to slide back and forth thereon.

Sonorescence. The property of producing sounds under the influence of momentary light radiations rapidly succeeding each other. It is the property utilized in the photophone, q. v.

Fig. 306. MORSE SOUNDER.

Sounder. In telegraphy an instrument consisting of an electromagnet with armature attached to an oscillating bar, the range of whose movements is restricted by adjusting screws. The armature is drawn away from the magnet by a spring. When a current is sent through the magnet the armature is drawn towards the poles and produces a sound as the bar strikes a striking piece or second adjusting screw. When the current ceases the bar and armature are drawn back, striking the first mentioned screw with a distinct sound, the back stroke.

The sounder is used to receive Morse and analogous character messages. The forward strokes correspond to the beginnings of the dots or dashes of the code, the back strokes to beginnings of the intervals. The distinction between dots and dashes is made by observing the interval between forward and back stroke.

Various devices are used to increase the sound. Sometimes a resonance box is used on which the sounder is mounted.

In practice sounders are generally placed on local circuits and are actuated by relays.

489 STANDARD ELECTRICAL DICTIONARY.

Sound Reading. The art or method of receiving telegraph messages by ear. It is now universally used by all expert Morse operators. It can only be applied to telegraph systems producing audible sounds; in some cases, as in needle telegraphy, it may be quite inapplicable.

Space, Clearance. The space between faces of the pole pieces and the surface of the armature in a dynamo. It is really the air gap, but in calculating dynamo dimensions the thickness of the insulated copper wire windings of the commutator are counted in as part of the air gap, because copper is almost the same as air in impermeability. Clearance space is a mechanical factor; the air gap is an electric or magnetic factor.

Synonym--Inter-air Space.

Space, Crookes' Dark. In an exhausted tube, through which an electric discharge is caused to pass, the space surrounding the negative electrode of the tube. This space is free from any luminous effect, and by contrast with the light of the discharge appears dark. The vacuum may be made so high that the dark space fills the whole space between the electrodes. It is less for a less vacuum and varies for other factors, such as the temperature of the negative electrode from which it originates, the kind of residual gas present, and the quality of the spark.

Space, Faraday's Dark. The space in an exhausted tube between the luminous glows about the two electrodes.

Space, Interferric. A term for the air-gap in a magnetic circuit. It is etymologically more correct than air-gap, for the latter is often two-thirds or more filled with the insulating material and copper wire of the armature windings. (See Space, Clearance.)

Spark Arrester. A screen of wire netting fitting around the carbons of an arc lamp above the globe to prevent the escape of sparks from the carbons.

Spark Coil. A coil for producing a spark from a source of comparatively low electro-motive force. It consists of insulated wire wound round a core of soft iron, best a bundle of short pieces of wire. Such a coil may be eight inches long and three inches thick, and made of No. 18-20 copper wire, with a core one inch in diameter. On connecting a battery therewith and opening or closing the circuit, a spark is produced by self-induction, q. v. It is used for lighting gas.

490 STANDARD ELECTRICAL DICTIONARY.

Spark, Duration of Electric. Wheatstone determined the duration of the spark given by a Leyden jar as 1/24000 second. Feddersen by interposing a tube of water 9 millimeters (.36 inch) long in its path found that it lasted 14/10000 second, and with one 180 millimeters (7.2 inches) long, 188/10000 second. Lucas and Cazin for a 5 millimeter (.2 inch) spark, with different numbers of Leyden jars, found the following: Number of jars. Duration of Spark. 2 .000026 second 4 .000041 " 6 .000045 " 8 .000047 "

The duration increases with the striking distance, and is independent of the diameter of the balls between which it is produced.

Spark Gap. The space left between the ends of an electric resonator (see Resonator, Electric) across which the spark springs. Its size may be adjustable by a screw, something like the arrangement of screw calipers.

Sparking. In dynamo-electric machines, the production of sparks at the commutator between the brushes and commutator sections. The sparks are often true voltaic arcs, and in all cases are injurious if in any quantity, wearing out the commutator and brushes.

Sparking, Line or Points of Least. In a dynamo or electric motor the diameter of the commutator determining, or the points on the commutator marking the position of the brushes where the sparking is a minimum. Field magnets powerful in proportion to the armature are a preventative cause. The direction of the line fixes the angle of lead to be given to the brushes.

Sparking, Resistance to. The resistance to disruptive discharge through its substance offered by a dielectric or insulator. It does not depend on its insulating qualities, but on its rigidity and strength.

Spark, Length of. The length of the spark accompanying the disruptive discharge is counted as the distance from one electrode to the other in a straight line. It is longer for an increased potential difference between the two electrodes. If the gas or air between the electrodes is exhausted the length increases, until the vacuum becomes too high, when the length begins to decrease, and for a perfect vacuum no spark however small can be produced. The shape of the conductor which is discharged, the material of the electrodes, and the direction of the current are all factors affecting the length of spark producible.

491 STANDARD ELECTRICAL DICTIONARY.

Spark Tube. A tube used as a gauge or test to determine when the exhaustion of the vacuum chamber or bulb of an incandescent lamp is sufficiently high.

The interior of the tube is connected with the interior of the bulb or chamber of the lamps in process of exhaustion, and hence shares their degree of exhaustion. From time to time connections with an induction coil are made. When the exhaustion is carried far enough no discharge will take place through the vacuum. As long as the tube acts like a Geissler tube the exhaustion is not considered perfect.

Specific Heat of Electricity. The heat absorbed or given out by a fluid in passing from one temperature to another depends on its specific heat. In the Peltier and the Thomson effects. q. v., the electric current acts as the producer of a change of temperature, either an increase or decrease as the case may be. This suggests an absorption of and giving out of heat which amount of heat corresponding to a current of known amount is determinable, and may be referred to any unit of quantity such as the coulomb. This or some equivalent definite quantity of heat it has been proposed (Sir William Thomson) to term the Specific Heat of Electricity.

Spent Acid. Acid which has become exhausted. In a battery the acid becomes spent from combination with zinc. It also loses its depolarizing power, if it is a chromic acid solution or of that type, and then may be said to be spent.

Spent Liquor. The liquor of a plating bath which has become exhausted from use, the metal it contained being all or partly deposited.

Sphygmograph, Electric. An electric apparatus for recording the beat of the pulse, both as regards its rate and strength.

Sphygmophone. An apparatus for examination of the pulse by the microphone and telephone.

Spiders. Core-discs of a dynamo or motor armature are sometimes perforated with a large central aperture, are fastened together with insulated bolts, and the whole mass is secured to the shaft by three- or four-armed spiders. These are like rimless wheels, the ends of their arms being secured to the hollow cylinder constituting the armature core, and a central aperture in their hub receiving the shaft.

492 STANDARD ELECTRICAL DICTIONARY.

Spiral. This term is sometimes used instead of coil, as the primary spiral or secondary spiral of an induction coil or transformer.

Spiral Winding. The winding used on ring armatures. This may diagrammatically be represented by a spiral carried around the ring shaped core. With two field poles it gives two collecting points, positive and negative, with four field poles it gives four collecting points, alternately positive and negative.

Splice Box. A box in which the splices in underground cables and electric lines are contained. The splicing is generally done in the boxes with the cables in place. They may be two-way for straight lines, or be four-way for two side or lateral connections.

Spluttering. A term applied to a sound sometimes produced in a voltaic arc, perhaps caused by impure or insufficiently baked electrodes. (Elihu Thomson.)

Spring Control. Control of or giving the restitutive force to the needle of a galvanometer, core of a solenoid ammeter or moving part of any similar instrument by a spring. As an example see Ammeter, Ayrton's.

Fig. 307. SPRING JACKS.

Spring Jack. An arrangement for effecting, at one insertion of a species of plug, the opening or breaking of a circuit and for the simultaneous connection to the terminals formed by the breaking of two terminals of another system or loop. Thus let a line include in its circuit two springs pressing against each other, thereby completing the circuit. If a plug or wedge of insulating material were inserted between the springs so as to press them apart it would break the circuit and the whole would constitute a spring jack cut-out. If each side of the plug had a strip of brass or copper attached to it, and if the ends of another circuit were connected to these strips, then the insertion of the plug would throw the new line into the circuit of the other line.

493 STANDARD ELECTRICAL DICTIONARY.

Spring Jack Cut-out. A cut-out, of the general construction of a spring jack, q. v., except that a simple insulating plug or wedge is used in place of the metal-faced wedge with its connections of the regular spring jack. The insertion of an insulating wedge opens the circuit, which on its removal is closed. The regular spring jack wedge will operate in the same way, if its connections are kept open.

Spurious Voltage. The voltage in excess of that developed by a secondary battery which is required in the charging process. It is about .25 volt.

Square Wire. Wire whose cross-section is a square. It has been used of iron for building up the cores of armatures for dynamos or motors, for which it is peculiarly suitable, and also of copper as a winding for armatures.

Staggering. adj. When the brushes of a dynamo are set, one a little in advance of the other on the surface of the commutator, they are said to be set staggering. It is used to get over a break in the armature circuit.

State, Electrotonic. A term expressing an abandoned theory. Faraday at one time proposed the theory that a wire had to be in the electrotonic state to produce electro-motive force by movement through an electric field. Any such idea was ultimately abandoned by Faraday.

Static Breeze. The electric breeze obtained by the silent discharge of high tension electricity.

Static Electricity. Electricity at rest or not in the current form ordinarily speaking. The term is not very definite and at any rate only expresses a difference in degree, not in kind. The recognition of the difference in degree has now to a great extent also disappeared.

Station, Central. The building or place in which are placed electrical apparatus, steam engines and plant supplying a district with electric energy.

Station, Distant. The place at the further end of a telegraph line, as referred to the home station.

Station, Home. The end of a telegraph line where the operators using the expression are working.

494 STANDARD ELECTRICAL DICTIONARY.

Station, Transforming. In alternating current distribution, a building or place where a number of transformers are worked, so that low potential or secondary circuits are distributed therefrom.

Steel. A compound of iron with carbon. The carbon may range from a few hundredths of one per cent. up to two per cent. For magnets, tool steel drawn to a straw color or a little lower is good. All shaping and filing should be done before magnetization.

Steeling. The deposition of iron on copper plates by electrolysis. In electrotyping a thin deposit of iron is thus given the relief plates before printing from them. The deposit is very hard and exceedingly thin, so that it does not interfere with the perfection of the impression in the printing process. As the iron becomes worn it can be dissolved off with hydrochloric acid, which does not dissolve the copper, and a new deposit can be given it. Thus the plate may last for an indefinite number of impressions.

The iron bath may be prepared by immersing in a solution of ammonium chloride, two plates of iron, connected as anode and kathode in a circuit. One plate dissolves while hydrogen is given off from the other. The solution thus produced is used for a bath.

The hardness of the deposit, which is really pure iron, gives the name of "steeling."

Synonym--Acierage.

St. Elmo's Fire. Luminous static discharge effects sometimes seen on objects elevated in the air. They are especially noticed on ships' masts. The sailors term them corpusants (holy bodies). They resemble tongues or globes of fire.

Step-by-step Telegraphy. A system of telegraphy in which in the receiving instrument a hand is made to move step-by-step, with an escape movement around a dial. For each step there is a letter and the hand is made to stop at one or the other letter until the message is spelled out. (See Dial Telegraph.)

Step-down. adj. A qualification applied to a converter or transformer in the alternating current distribution, indicating that it lowers potential difference and increases current from the secondary.

Step-up. adj. The reverse of step-down; a qualification of a transformer or converter indicating that it raises the potential and decreases the current in the secondary.

Sticking. The adherence, after the current is cut off, of the armature to the poles of a magnet. In telegraphy it is a cause of annoyance and obstructs the working. It may, in telegraphy, be due to too weak a spring for drawing back the armature, or to imperfect breaking of the contact by the despatcher's key or by the receiver's relay.

495 STANDARD ELECTRICAL DICTIONARY.

Stopping Off. In electroplating the prevention of deposition of the plating metal on any desired portions of the object. It is effected by varnishing the places where no coating is desired. An article can be plated with silver, stopped off in any desired design, and the unvarnished portions may then be plated with gold in another bath. Various effects can be produced by such means.

Storage Capacity. A term for the ampere-hours of electricity, which can be taken in current form from a storage battery.

Storage of Electricity. Properly speaking electricity can only be stored statically or in static condensers, such as Leyden jars. The term has been popularly applied to the charging of secondary or storage batteries, in which there is really no such thing as a storage of electricity, but only a decomposition and opposite combination brought about, which leave the battery in a condition to give a current.

Storms, Electric. Wide-spread magnetic and electric disturbances, involving the disturbance of the magnetic elements and other similar phenomena. (See Magnetic Storms.)

Strain. The condition of a body when subjected to a stress. Various consequences may ensue from strain in the way of disturbance of electric and other qualities of the body strained.

Stratification Tube. A Geissler tube, q. v., for showing the stratification of the electric discharge through a high vacuum.

The stratifications are greatly intensified by the presence of a little vapor of turpentine, alcohol, bisulphide of carbon and other substances.

Stray Field. In a dynamo or motor the portion of the field whose lines of force are not cut by the armature windings.

Stray Power. The proportion of the energy wasted in driving a dynamo, lost through friction and other hurtful resistances.

Streamlets, Current. A conception bearing the same relation to an electric current that lines of force do to a field of force; elementary currents. If evenly distributed the current is of uniform density; if unevenly distributed, as in alternating currents, the current density varies in different parts of the cross section of the conductor. This evenness or unevenness may be referred to the number of streamlets per unit of area of cross-section.

[Transcriber's note: Streamlets per unit of area is redundant with current density.]

Stress. Force exercised upon a solid tending to distort it, or to produce a strain.

496 STANDARD ELECTRICAL DICTIONARY.

Stress, Dielectric. The condition of a dielectric when maintaining a charge; its two extremities are in opposite states of polarity, or are under permanent potential difference. As the two opposite polarities tend to unite a condition of stress is implied in the medium which separates them.

Stress, Electro-magnetic. The stress produced upon transparent substances in an electro-magnetic field of force. It is shown in the modified optical properties of glass and similar substances placed between the poles of a strong electro-magnet.

Stress, Electrostatic. The stress produced upon substances in an electrostatic field of force; the exact analogue of electro-magnetic stress, and affecting transparent substances in the same general way.

Striae, Electric. In Geissler tubes the light produced by the electric discharge is filled with striae, bright bands alternating with dark spaces; these may be termed electric striae.

Striking Distance. The distance that separates two conductors charged with electricity of different potential, when a spark starts between them.

Striking Solution. In silver-plating a bath composed of a weak solution of silver cyanide-with a large proportion of free potassium cyanide. It is used with a strong current and a large silver anode. This gives an instantaneous deposition of metallic silver over the surface of the article which goes to insure a perfect coating in the silver bath proper. After a few seconds in the striking solution, the article is at once removed to the plating bath.

Stripping. The removal of electroplating from an object. It may be effected in several ways. An object whose plating is to be removed is placed in a plating bath of the solution of the metal with which it is coated. It is connected as the anode to the positive plate of the battery or corresponding terminal of the generator. A kathode connected to the other terminal being placed in the bath, the coating is dissolved by electrolytic action. Sometimes simple treatment with acid is employed. Different stripping baths are described under the heads of the different metals.

S. U. Symbol or abbreviation for Siemens' Unit of Resistance. (See Resistance, Siemens' Unit of.)

Sub-branch. A branch or lead of wire taken from a branch lead: a term used in electric distribution.

Sub-main. In electric distribution a conductor connected directly to a main; a branch.

497 STANDARD ELECTRICAL DICTIONARY.

Subway, Electric. A subterranean system of conduits for electric cables. As generally constructed in this country it includes manholes, q. v., at the street corners connected by ducts or pipes. These pipes are large enough to hold a cable. To introduce a cable into a duct, which latter may be two or three inches in diameter, and from two hundred to six or seven hundred feet long, a wire or rope is first passed through the duct. This is done by a set of short wooden rods with screws at the end so as to be screwed together. Each rod must be shorter than the diameter of the manhole. A rod is thrust in, another is screwed to it and thrust in, and thus a set of rods is made to extend as far as desired. In pulling them out a rope is attached and drawn through. This rope or a larger one is used in drawing the cable through the duct. A windlass is employed to draw the rope with cable attached through the ducts.

Sulphating. In storage battery cells, the formation of a hard white basic lead sulphate, Pb2 S05. Its formation is due to over-exhaustion of the cells. As long as the voltage is not allowed to fall below 1.90 volts per cell little of it forms. As it accumulates it is apt to drop off the plate and fall to the bottom, thus weakening the plate possibly, and depriving it of active material, and clogging up the cell. If it carries a film of metallic lead with it, there is danger of short circuiting the cell.

The presence of some sodium sulphate in the solution is said to tend to prevent sulphating, or to diminish it.

Sulphur Dioxide. A compound gas, S O2; composed of Sulphur, 32 Oxygen, 32 Molecular weight, 64 Specific gravity, 2.21.

It is a dielectric of about the same resistance as air. Its specific inductive capacity at atmospheric pressure is: 1.0037 (Ayrton).

Synonyms--Sulphurous Acid--Sulphurous Acid Gas.

Sunstroke, Electric. Exposure to the arc light sometimes produces the effects observed in cases of sunstroke. It is said that, in the case of workmen at electric furnaces, these effects are very noticeable. (See Prostration, Electric.)

[Transcriber's note: Effects are due to ultraviolet light.]

Supersaturated. adj. A liquid is supersaturated when it has dissolved a substance at a temperature favorable to its solubility and its temperature has been allowed to change, the liquid being kept free from agitation or access of air, provided crystallization or precipitation has not taken place. It expresses the state of a liquid when it holds in solution more than the normal quantity of any substance soluble in it.

Surface. A galvanic battery is arranged in surface when all the positive plates are connected together and all the negative plates are also connected. This makes it equivalent to one large cell, the surface of whose plates would be equal to the aggregate surface of the plates of the battery. It is also used as an adjective, as "a surface arrangement of battery."

498 STANDARD ELECTRICAL DICTIONARY.

Surface Density. The relative quantity of an electric charge upon a surface.

Surface, Equipotential. A surface over all of which the potential is the same. In a general sense equipotential surfaces are given by planes or surfaces which cut lines of force at right angles thereto, or which are normal to lines of force. The conception applies to electrostatic and electro-magnetic fields of force, and for current conductors the planes normal to the direction of the current are equipotential surfaces.

The contour of an equipotential surface of a field of force which is drawn or represented by delineations of its lines of force can be obtained by drawing a line normal thereto. This line will ordinarily be more or less curved, and will be a locus of identical potentials.

An electric equipotential surface may be described as electro-static, electro- magnetic, or magnetic; or may be an equipotential surface of a current conductor. Besides these there are mechanical and physical equipotential surfaces, such as those of gravitation.

Surface Leakage. Leakage of current from one part of an insulating material to another by the film of moisture or dirt on the surface.

Suspension. This term is applied to methods of supporting galvanometer needles, balance beams, magnetic compass needles and similar objects which must be free to rotate. (See Suspension, Bifilar--Fibre and Spring Suspension--Fibre Suspension--Knife Edge Suspension--Pivot Suspension--Suspension, Torsion.)

308. DIAGRAM OF BIFILAR SUSPENSION.

Suspension, Bifilar. Suspension by two vertical parallel fibres, as of a galvanometer needle. The restitution force is gravity, the torsion being comparatively slight and negligible. Leaving torsion out of account the restitution force is (a) proportional to the distance between the threads;. (b) inversely proportional to their length; (c) proportional to weight of the needle or other object suspended; (d) proportional to the angle of displacement.

499 STANDARD ELECTRICAL DICTIONARY.

Assume two masses A and B at the end of a weightless rod, suspended by the parallel cords a A, b B. Let the rod be rotated through an angle theta. Consider the cord a A. Its lower end is swung through the angle theta, as referred to the center O; the cord is deflected from the vertical by an angle psi, such that a A tang(psi)= O A 2 sin (theta/2). The component of gravitation tending to restore A to A, acting towards A is equal to m g tan(psi). Its moment around O is equal to (m g tan(psi)) * (O A cos(theta/2). The whole moment of the couple is 2 m g tan(psi). 0 A. cos(theta/2) = 2 m g (O A2/ a A) 2 sin(theta/2). Cos(theta/2) = 2mgl(OA2/aA) sin(theta). The moment of the restoring force is thus proportional to the sine of the angle of deflection, and the oscillations of such a system are approximately simple harmonic. (Daniell.)

If the twisting is carried so far as to cause the threads to cross and come in contact with each other the suspension ceases to be a bifilar suspension, but assumes the nature of a torsional suspension.

[Transcriber's note: This is the image of the first paragraph.]

Swaging, Electric. Mechanical swaging in which the objects to be swaged are heated by an electric current as in electric welding.

S. W. G. Abbreviation for Standard Wire Gauge.

Fig. 309. SIMPLE SWITCH.

Switch. A device for opening and closing an electric circuit.

A simple type is the ordinary telegrapher's switch. A bar of metal is mounted horizontally by a pivot at one end, so as to be free to rotate through an arc of a circle. In one position its free end rests upon a stud of metal. One terminal of a circuit is attached to its journal, the other to the stud. Resting on the stud it closes the circuit, in other positions it opens the circuit.

500 STANDARD ELECTRICAL DICTIONARY.

Switch, Automatic. A switch opened and closed by the electric current. It is used for lighting distant incandescent lamps. It includes one or two electro-magnets operated by two push buttons. In the usual arrangement one button is black and the other white, for extinguishing and lighting respectively. When the white button is pushed it causes a current to pass through one of the electro-magnets. This attracts its armature, thereby making a contact and throwing the lamps into the lighting circuit. Then they remain lighted until the black button is pressed. This excites the other magnet, which attracts its armature, breaks the contact and extinguishes the lights.

The object of the automatic switch is to enable distant lamps to be lighted without the necessity of carrying the electric leads or wires to the place whence the lighting is to be done. A very small wire will carry enough current to operate the magnets, and open circuit batteries, such as Leclanché batteries, may be used as the source of current for the switch, but generally the lighting current is used for the purpose.

A single magnet may do the work. When the lighting button is pressed the magnet is excited, attracts its armature and holds it attracted, until by pressing the black button the current is turned off from it. In this case the lighting current is used to excite the magnet.

Switch Board. A board or tablet to which wires are led connecting with cross bars or other switching devices, so as to enable connections among themselves or with other circuits to be made.

Switch, Circuit Changing. A switch whose arm in its swing breaks one contact and swinging over makes another. It is employed to change the connections of circuits from one dynamo to another.

Synonyms--Changing Switch--Changing Over Switch.

Switch, Double Break. A form of switch in which double contact pieces are provided to give a better contact. One form consists of a hinged bar whose end swings down between two pairs of springs. Both pairs are connected to one terminal, and the bar to the other terminal of a circuit.

Switch, Double Pole. A heavy switch for central station work, that connects and disconnects two leads simultaneously.

Switch, Feeder. A heavy switch, often of double contact type, for connecting and disconnecting feeders from bus bars in central stations.

501 STANDARD ELECTRICAL DICTIONARY.

Switch, Knife. A switch whose movable arm is a narrow, deep bar of copper or brass, and which in making contact is forced in edgeways between two springs connected to one terminal. The bar is connected to the other terminal.

Synonyms--Knife Break Switch--Knife Edge Switch.

Switch, Multiple. A switch which in the swing of its bar connects one by one with a number of contacts so that ultimately the end of its bar is in contact with all at once. It is used to throw lights in and out in succession, and it can, if the multiple contacts connect with resistances, make them operate as a rheostat.

Switch, Pole Changing. A switch for changing the direction of the current in a circuit.

Switch, Reversing. A switch, often of the plug type (see Plug Switch) for changing the direction of current passing through a galvanometer.

Switch, Snap. A switch constructed to give a quick, sharp break. It has a spiral spring interposed between the handle and arm. As the handle is drawn back to open it the spring is first extended, the bar being held by the friction of the contacts, until the spring suddenly jerks it up, thus breaking the contact.

Switch, Storage Battery Changing. A switch for changing storage battery connections from series to multiple and back again.

Switch, Three Way. A switch, so constructed that by turning its handle connection can be made from one lead to either of two other leads, and also so that connection can be completely cut off.

Sympathetic Vibration. The establishment of periodic movement in one body by impulses of the same period communicated to it from another body in motion. Thus if two tuning forks are of the same pitch and one is sounded the other will begin to sound by sympathy, the sound waves communicating the necessary periodic impulses to it.

Sympathetic vibrations are utilized in harmonic telegraphy. (See Harmonic Receiver--Telegraph, Harmonic.)

T. Symbol of time.

Tailings. (a) In high speed transmission of telegraph signals by the automatic system, the definiteness of the signal marks is sometimes interfered with by retardation. Wrong marks are thus produced called tailings.

(b) The prolongation of the current at the distant receiving station of a telegraph line due to the discharge of the line and to self-induction.

Synonyms--Tailing--Tailing Current.

502 STANDARD ELECTRICAL DICTIONARY.

Tamidine. Reduced nitro-cellulose. Nitro-cellulose is dissolved in a proper solvent and is obtained by evaporation as a translucent solid mass. By ammonium sulphide or other reagent it is reduced so as to be virtually cellulose. It is cut into shape for filaments of incandescent lamps, which shapes are carbonized and flashed.

Tangent Law. In a galvanometer the tangents of the angles of deflection of the needle are proportional to the deflecting force--

I. When the controlling force is unaltered in absolute magnitude and direction by the motion of the needle.

II. When the deflecting force acts at right angles always to the controlling force.

These conditions are usually secured by having the actuating coil through which the current passes flat and of large diameter compared to the length of the needle; by using the uniform field of the earth as the control; by having a short needle; by placing the coil with its plane in the magnetic meridian.

For best proportions of tangent galvanometer coils see Bobbins.

Fig. 310. GRAPHIC CONSTRUCTION OF TANGENT SCALE.

Tangent Scale. An arc of a circle in which the number of graduations in any arc starting from zero are proportional to the tangent of the angle subtended by such arc. The system is for use with tangent galvanometers. Thus if for 45° a value of 100 is taken and marked on the scale then for the arc 26° 33' + a value of 50 should be marked on the scale because such are the relative values of the tangents.

Thus the scale instead of being divided into degrees is divided into arcs of varying length, growing shorter as they are more distant from the zero point, of such length that the first division being subtended by a tangent of length 1, the first and second divisions added or taken together as one arc are subtended by a tangent of length 2, and so on.

In the cut a simple method of graphically laying out a tangent scale is shown. In it C is the centre of the arc, and H the radius running to the zero of the instrument. From C a circle is described and on H a vertical line tangent to the arc is erected. Taking any part of the tangent, as the length shown ending at D, it is divided into any number of equal parts. Radii of the circle are now drawn whose prolongations pass through the divisions on the tangent. These radii, where they intersect the arc of the circle, determine equal divisions of the tangent scale, which, as is evident from the construction, are unequal angular divisions of the arc.

503 STANDARD ELECTRICAL DICTIONARY.

Tanning, Electric. The tanning of hides in the manufacture of leather by the aid of electrolysis. A current of electricity is maintained through the tanning vats in which regular tanning liquor is contained. Very extraordinary claims are made for the saving of time in the tanning process. What is ordinarily a process of several months, and sometimes of a year, is said to be reduced to one occupying a few days only. The action of electrolysis is the one relied on to explain the results.

Tapper. The key used in single needle telegraph transmitters. It comprises two flat springs L, E, each with a handle, normally pressed upward against one contact bar Z, and when pressed down by the operator making contact against a lower bar C when messages are to be transmitted. A double tapper, such as shown, is used for each instrument.

Synonyms--Double Tapper Key--Pedal Key.

Fig. 311. TAPPER.

Target, Electric. A target registering or indicating electrically upon an annunciator the point of impact of each bullet.

Taste, Galvanic. The effect produced upon the gustatory nerves by the passage of an electric current, or by the maintenance of potential difference between two portions of the tongue. It is very simply produced by placing a silver coin above, and a piece of zinc below the tongue, or the reverse, and touching their edges. A sour, peculiar taste is at once perceived. It cannot be due to any measurable quantity of current or of electrolytic decomposition, because the couple can do little more than establish a potential difference. With a strong current the taste becomes too strong for comfort, and if on a telegraph line the extra currents produced by the signaling make the operation of tasting the current a very unpleasant one. It is said that messages have been received in this way, the receiver placing one terminal of the line on his tongue, and a terminal attached to a grounded wire below it, and then receiving the Morse characters by taste.

504 STANDARD ELECTRICAL DICTIONARY.

Teazer. Originally a fine wire coil wound on the field magnets of a dynamo in shunt with the regular winding to maintain the magnetism. It was originally used in electroplating machines to prevent inversion of the magnetism, but has since developed into a component part of the winding of the compound dynamo. (See Dynamo, Compound.)

Tee, Lead. A lead pipe of T shape used for connecting branches to electric cables. The tee is soldered by wiped joints to the lead sheathings of the cable and branches after the wires have been connected, and the junctions coated with insulating tape or cement, or both.

It is sometimes made in two halves, and is known as a split tee.

Tel-autograph. A telegraph for reproducing the hand-writing of the sender at the receiving end of the line. To save time a special spelling is sometimes used.

Teleautograph. The special spelling used with the Tel-Autograph telegraph.

Tele-barometer, Electric. A barometer with electric attachment for indicating or recording at a distance the barometric readings.

Telegraph, ABC. This term is applied to alphabet telegraphs indicating the message by the movements of a pointer on a dial marked with the characters to be sent. In England the Wheatstone ABC system is much employed.

Telegraph, Automatic. A telegraph system based on the operation of the transmitting instrument by a perforated strip of paper drawn through it. The perforations made by an apparatus termed a perforator, are so arranged as to give telegraphic characters of the Morse or International Code in the transmitting instrument. (See Perforator.) Bain in the year 1846 was the originator of the system. He punched a fillet of paper with dots and dashes, and drew it between two terminals of the line, thus sending over the line a corresponding series of short and long currents which were received by his chemical receiver. (See Chemical Receiver.) The method was not successful. Its modern development, the Wheatstone Automatic Telegraph, is highly so. The perforated paper by its perforations controls the reciprocating movement of two rods, which pass through each hole in two rows, corresponding to the two rods respectively as the holes come opposite to the ends of the rods. The rods are kept constantly moving up and down. If unperforated paper is above them their upward motion is limited. This gives three positions for the rods, (a) both down, (b) one up and the other down, (c) both up. These positions of the rods work a pole changing key by which dots, spaces, and dashes are transmitted to the receiving instrument, which is an exceedingly delicate ink-printer. The latter can have its speed adjusted to receive from 200 to 450 words per minute.

505 STANDARD ELECTRICAL DICTIONARY.

Telegraph, Dial. A telegraph in which as receiver a dial instrument is used. A pointer or index hand moves around a dial. The dial is marked with letters of the alphabet. The movements of the pointer are controlled by the transmitting operator at a distant station. He by the same actions moves a pointer on a duplicate instrument before him and the two are synchronized to give identical indications. Thus a message is spelled out letter by letter on both dials simultaneously. The motions of the index are generally produced by what is virtually a recoil escapement. The scape wheel is carried by the axle of the index, and a pallet or anchor is vibrated by an electro-magnet whose armature is attached to the stem of the pallet. As the pallet is vibrated it turns the wheel and index one tooth for each single movement. There are as many teeth in the wheel as there are characters on the dial. The two instruments being in duplicate and synchronized, the pallets move exactly in unison, so that identical readings of the dials are given. The pallets may be moved by any kind of make and break mechanism, such as an ordinary telegraph key. The index moves by steps or jerks, so that the system is sometimes called step-by-step telegraphy.

Fig. 312. DIAL TELEGRAPH.

In the cut the make and break transmitter is shown at v v, with its handle and contacts g and t. This mechanism sends impulses of current by F and Z to the receiving magnet l. This attracts and releases its armature K from contact into the position indicated by the dotted lines. This works the rocker n on the pin o, and actuates the double or anchor pawl s r, which turns the pallet or scrape wheel m.

The system is dropping into disuse, being supplanted by the telephone.

Synonym--Step-by-step Telegraph.

506 STANDARD ELECTRICAL DICTIONARY.

Telegraph, Double Needle. A telegraph system in which the message is read by the motions of two vertical needles on the face of the instrument in front of the receiving operator. An identical instrument faces the transmitting operator. By two handles, one for each hand, the needles are caused by electric impulses to swing to right and to left so as to give a telegraphic code. It has been generally superseded by the single needle telegraph.

Telegraph, Duplex. A telegraph capable of transmitting simultaneously two messages over one wire. The methods of effecting it are distinct from those of multiplex telegraphy. This term is used as a distinction from diode multiplex telegraphy, in which the work is done on other principles. There are two systems of duplex telegraphy, the differential and the bridge systems.

Telegraph, Duplex Bridge. A system of duplex telegraphy employing the principle of the Wheatstone bridge. The other or differential system depends on equality or difference of currents; the bridge method on equality or difference of potentials. The cut shows the system known as Steam's Plan.

At the ends of the line wire are two cross connections like duplicate galvanometer connections in a Wheatstone bridge, each including a receiving relay. The rest of the connections are self-explanatory.

When A depresses his key the current splits at the point indicating the beginning of the bridge. One portion goes through the line to B and to earth, the other goes to earth at A through the rheostats indicated by the corrugated lines.

On reaching B's end the current divides at the cross-connection and part goes through the receiving relay shown in the center of that cross-connection.

Thus if A sends to B or B to A it is without effect on the home receiving instrument. Now suppose that both simultaneously are sending in opposite directions. If the connections be studied it will be seen that every movement of the transmitting key will affect the balance of the distant or receiving end of the bridge and so its instrument will record the signals as they are sent.

As shown in the cut the sending keys are on local circuits, and work what are known as duplex transmitters. These are instruments which send line signals without breaking the connection.

Fig. 313. STEARN'S PLAN OF DUPLEX BRIDGE TELEGRAPHY.

In Stearn's plan condensers are introduced as shown. By this plan different receiving instruments can be used. The inventor once worked a Morse instrument at one end of the line, and a Hughes' instrument at the other end.

507 STANDARD ELECTRICAL DICTIONARY.

Telegraph, Duplex, Differential. A system of duplex telegraphy employing the differential action of two exciting or magnetizing coils. The general principles are the following. Suppose that at each of two stations, there is a magnet working as a sounder or relay. Each magnet is differentially wound, with two coils of opposite direction, of identical number of turns.

When the sending key at a station A is depressed two exactly equal currents go through the magnet in opposite directions. One called the compensation current goes to the earth at the stations. The other called the line current goes through the line, through the line coil of the distant station E, thereby actuating the relay or sounder armature.

The instrument of the sender A is unaffected because he is sending opposite and equal currents through its two coils. A special resistance is provided on the compensation circuit for keeping the currents exactly equal in effect. Nothing the sender at A does affects his own instrument.

Now suppose E desires to telegraph back at the same time that A is telegraphing to his station. He works his key. This does not affect his own instrument except by sending the equal and opposite currents through its coils. When his key is depressed and A's key is untouched, he works A's receiving instrument.

508 STANDARD ELECTRICAL DICTIONARY.

When A's key is depressed simultaneously with B's key, the two line currents are in opposition and neutralize each other. This throws out the balance in the instruments and both armatures are attracted by the compensation currents left free to act by the neutralization of the line currents.

Fig. 314. DUPLEX TELEGRAPH, DIFFERENTIAL SYSTEM

Suppose that B is sending a dash, and it begins while A's key is raised. The line and compensation currents in B's receiving instrument neutralize each other and no effect is produced, while A's receiving instrument begins to register or indicate a dash. Now suppose A starts to send a dash while B's is half over. He depresses his key. This sends the two opposite currents through his magnet. His line current neutralizes B's working current so that the compensation currents in both receiving instruments hold the armatures attracted for the two dashes. Meanwhile A's dash ends and he releases his key. At once his line current ceases to neutralize B's line current, his receiving instrument is actuated now by B's line current, while B's receiving instrument ceases to be actuated by the compensation current.

Two assumptions are made in the above description. The line currents are assumed to be equal in strength and opposite in direction at each station. Neither of these is necessary. The line current received at a station is always weaker than the outgoing line current, and it is the preponderance of the compensation current over the partly neutralized line current that does the work. As this preponderance is very nearly equal to the line current received from the distant station, the signals are actuated by almost the same current, whether it is compensation or line current.

509 STANDARD ELECTRICAL DICTIONARY.

Both line currents may coincide in direction. Then when the two keys are depressed, a line current of double strength goes through both receiving instruments and both work by preponderance of the double line current over the compensation current. In other respects the operation is the same as before described.

Fig. 315. DUPLEX TELEGRAPH, DIFFERENTIAL SYSTEM.

Fig. 316. DIFFERENTIAL DUPLEX TELEGRAPH CONNECTIONS.

The cut shows a diagram of the operation of one end of the line. R and R are resistances, E and E are earth contacts, and the two circles show the magnet of the receiving instrument wound with two coils in opposition. The battery and key are also shown. It also illustrates what happens if the key of the receiver is in the intermediate position breaking contact at both 1 and 2. The sender's line current then goes through both coils of the receiving instrument magnet, but this time in series, and in coincident direction. This actuates the instrument as before. Owing to the resistance only half the normal current passes, but this half goes through twice as many coils or turns as if the receiver's key was in either of the other two positions.

In actual practice there are many refinements. To compensate for the varying resistance of the line a rheostat or resistance with sliding connection arm is connected in the compensation circuit so that the resistance can be instantly changed. As the electro-static capacity of the line varies sectional condensers are also connected in the compensation circuits.

510 STANDARD ELECTRICAL DICTIONARY.

Telegraph, Facsimile. A telegraph for transmitting facsimiles of drawing or writing. The methods employed involve the synchronous rotation of two metallic cylinders, one at the transmitting end, the other at the receiving end.

On the transmitter the design is drawn with non-conducting ink. A tracer presses upon the surface of each cylinder and a circuit is completed through the two contacts. In operation a sheet of chemically prepared paper is placed over the surface of the receiving cylinder. The two cylinders are rotated in exact synchronism and the tracers are traversed longitudinally as the cylinders rotate. Thus a number of makes and breaks are produced by the transmitting cylinder, and on the receiving cylinder the chemicals in the paper are decomposed, producing marks on the paper exactly corresponding to those on the transmitting cylinder.

Synonyms--Autographic Telegraph--Pantelegraphy.

Telegraph, Harmonic Multiplex. A telegraph utilizing sympathetic vibration for the transmission of several messages at once over the same line. It is the invention of Elisha Gray. The transmitting instrument comprises a series of vibrating reeds or tuning-forks, each one of a different note, kept in vibration each by its own electro-magnet. Each fork is in its own circuit, and all unite with the main line so as to send over it a make and break current containing as many notes superimposed as there are tuning forks. At the other end of the line there are corresponding tuning forks, each with its own magnet. Each fork at this end picks up its own note from the makes and breaks on the main line, by the principle of sympathetic vibration.

To each pair of operators a pair of forks of identical notes are assigned. As many messages can be transmitted simultaneously as there are pairs of forks or reeds.

The movements of a telegraph key in circuit with one of the transmitting reeds sends signals of the Morse alphabet, which are picked out by the tuning fork of identical note at the other end of the line.

511 STANDARD ELECTRICAL DICTIONARY.

Telegraph, Hughes'. A printing telegraph in very extensive use in continental Europe. Its general features are as follows:

The instruments at each end of the line are identical. Each includes a keyboard like a piano manual, with a key for each letter or character. On each machine is a type wheel, which has the characters engraved in relief upon its face. With the wheel a "chariot" as it is termed also rotates. The type wheels at both stations are synchronized. When a key is depressed, a pin is thrown up which arrests the chariot, and sends a current to the distant station. This current causes a riband of paper to be pressed up against the face of both type wheels so as to receive the imprint of the character corresponding to the key. The faces of the wheels are inked by an inking roller.

Fig. 317. ELECTRO-MAGNET OF HUGHES' PRINTING TELEGRAPH.

The most characteristic feature is the fact that the current sent by depressing a key does not attract an armature, but releases one, which is then pulled back by a spring. The armature is restored to its position by the mechanical operation of the instrument. The magnet used is a polarized electro-magnet. Coils are carried on the ends of a strong powerful magnet. The coils are so connected that a current sent through them by depressing a key is in opposition to the magnetism of the permanent magnet so that it tends to release the armature, and in practice does so. This release permits the printing mechanism to act. The latter is driven by a descending weight, so that very slight electric currents can actuate the instruments.

Synonym--Hughes' Type Printer.

Telegraphic Code. (a) The telegraphic alphabet, as of the Morse System. (See Alphabet, Telegraphic.)

(b) A code for use in transmitting messages either secretly, or comprising several words or short sentences in one word, in order to economize in transmission. Such codes are extensively used in commercial cable messages.

512 STANDARD ELECTRICAL DICTIONARY.

Telegraph, Magneto-electric. A telegraph in which the current is produced by magneto-electric generators. It has been applied to a considerable extent in England. The Wheatstone ABC or dial telegraph is operated by a magneto-generator turned by hand.

In this country the magneto-electric generator by which the calling bell of a telephone is rung is an example. The magneto-electric key (See Key, Magneto-electric) is for use in one kind of magneto-electric telegraphing.

Telegraph, Morse. A telegraph, characterized by the use of a relay, working a local circuit, which circuit contains a sounder, or recorder for giving dot and dash signals constituting the Morse alphabet. The signals are sent by a telegraph key, which when depressed closes the circuit, and when released opens it. The two underlying conceptions of the Morse Telegraph system are the use of the dot and dash alphabet, and the use of the local circuit, which circuit includes a receiving instrument, and is worked by a relay, actuating a local battery. It would be difficult to indicate any invention in telegraphy which has had such far-reaching consequences as the one known as the Morse telegraph.

In other places the principal apparatus of the system will be found described. The cut Fig. 318, repeated here gives the general disposition of a Morse system. (See Circuit, Local.)

Fig. 318. DIAGRAM OF MORSE SYSTEM.

513 STANDARD ELECTRICAL DICTIONARY.

The key by which the messages are transmitted is shown in Fig. 319. M is a base plate of brass. A is a brass lever, mounted on an arbor G carried between adjustable set screws D. C is the anvil where contact is made by depressing the key by the finger piece B of ebonite. E, Fl are adjusting screws for regulating the vertical play of the lever. H is the switch for opening or closing the circuit. It is opened for transmission, and closed for receiving. By screws, L L, with wing nuts, K K, the whole is screwed down to a table.

Fig. 319. MORSE TELEGRAPH KEY.

In the United States the simplest disposition of apparatus is generally used. The main line is kept on closed circuit. In it may be included a large number of relays at stations all along the line, each with its own local circuit. There may be fifty of such stations. Battery is generally placed at each end of the line. Very generally gravity batteries are used, although dynamos now tend to supplant them in important stations.

As relays the ordinary relay is used. Its local circuit includes a sounder and local battery. The latter is very generally of the gravity type, but oxide of copper batteries (See Battery, Oxide of Copper) are now being introduced. At main or central offices, the terminals of the lines reach switch boards, where by spring-jacks and plugs, any desired circuits can be looped into the main circuit in series therewith.

In European practise the main line is kept on open circuit. Polarized relays are used to work the local circuits. The currents for these have to be alternating in direction. When the line is not in use its ends are connected to earth at both ends, leaving the battery out of circuit. Each intermediate station has its own main, or line battery for use when it desires to send a message. In the American system as first described, it will be seen that the main batteries are at most two in number.

For the details of the different apparatus, the following definitions may be consulted: Embosser, Telegraphic--Recorder, Morse--Relay--Relay Connection--Sounder.

514 STANDARD ELECTRICAL DICTIONARY.

Telegraph, Multiplex. A system of telegraphy by which a number of messages can be transmitted in both directions over a single wire. The principles underlying the systems are the following:

Suppose that at the two extremities of a telegraph line two arms are kept in absolute synchronous rotation. Let the arms in their rotation, press upon as many conducting segments as there are to be transmissions over the line. A transmitting and receiving set of instruments may be connected to one segment at one end of the line, and another set to the corresponding segment at the distant station. For each pair of segments two sets can be thus connected. Then if the arm rotates so rapidly that the contacts succeed each other rapidly enough each pair of sets of instruments can be worked independently of the others. In practice this rapid succession is effected by having a number of contacts made for each pair during a single rotation of the arm or equivalent.

The multiplex system has been perfected by the use of La Cour's phonic wheel (see Phonic Wheel), and brought into a practical success by Patrick B. Delany, of New York.

Two phonic wheels rotate at each end of the line. They are kept in synchronous motion by two vibrating steel reeds of exactly the same fundamental note, and the axle of each wheel carries an arm whose end trails over the contacts or distributor segments already spoken of. The reeds are adjusted to vibrate at such speed that the trailer is in contact with each segment about 1/500 second. The number of groups of segments required for each working is determined by the retardation of the signals owing to the static capacity of the line. To convert the rapidly recurring impulses of current into practically a single current, condensers are connected across the coils of the relay. One battery serves for all the arms.

Multiplex telegraphy can effect from two to six simultaneous transmissions over one wire. For two or four transmissions the method only distinguishes it from duplex or quadruplex telegraphy. The terms diode, triode, tetrode, pentode and hexode working are used to indicate respectively the simultaneous transmission of two, three, four, five, or six messages over one wire.

It will be seen that the multiplex process really assigns to each transmission separate times, but divides these times into such short and quickly recurring intervals that the work is executed as if there was continuous contact. In no case is there the popular conception of the sending of several messages actually simultaneously over one wire. Each signal in reality has its own time assigned it, divided into short periods of high frequency, and only utilizes the line when it is free.

515 STANDARD ELECTRICAL DICTIONARY.

Telegraph, Over-house. An English term for telegraph lines led over houses and supported on standards on the roofs.

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