Hawkins Electrical Guide: Questions, Answers & Illustrations; a Progressive ...

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Preface

The word "guide " is defined as :

One who leads another in any path or direction; a person who shows or points out the way, especially by accompanying or going before; more particularly, one who shows strangers or tourists about; a conductor; leader, as €t letus follow our guide J

This book, or "Guide," is so called because it leads or points out the way to the acquirement of a theoretical and practical knowledge of Electricity.

There are several guides, each covering in detail a certain phase of the broad subject of Electricity and leading the reader progressively^ and in such a way, that he easily grasps, not only the simple fundamental facts, but the more complex problems, encountered in {he study of Electricity. This is accomplished by the aid of a very large number of illustrations, together with specific explanations, worded in concise and simple language.

The Guides are written partly in the question and answer form f as this style of presentation has met with hearty approval, not only from those of limited education, but also from the better informed.

Where recourse is had to the question and answer form, the special aim of the author has to^to uy^fort and direct answers, in such plain language as to preclude a misconception of the meaning. With this in view, the answer gives simply the information sought by the question.

The answer is limited to one paragraph so that the reader may concentrate upon the fact or facts demanded by the question.

Any enlargement of the answer or specific explanations of items contained therein, are presented in separate paragraphs printed in smaller type.

With this, plan of separating the answer, as it were, from items of secondary importance, and making it short and simple, its content is more forcibly impressed upon the mind of the reader.

In a text book, it is necessary to illustrate and explain the various species of commercial apparatus met with in practice, and in this connection the Publishers desire to call attention to the manner in which the author has treated what may be classed as the "descriptive matter." Contrary to the usual custom of giving descriptions of commercial machines in the main text, where they would occupy considerable space, to the exclusion of the more important matter, all such descriptions are placed in small type directly under the illustrations, leaving space for an adequate presentation of the underlying principles, theories, and for the large amount of practical information that is essential to obtain a general knowU edge of Electricity and its numerous applications.

Credit is largely due to Frank D. Graham, B.S., M.S. (Princeton University), and M.E. (Stevens Institute), practical engineer, for the authorship of the Guides, and for original sketches illustrating electrical principles and construction.

TABLE OF CONTENTS; GUIDE NO. I

TABLE OF CONTENTS GUIDE NO. 1.

ELECTRICITY 1 to 4

Nature and source — kinds of electricity: static, current, dynamic, radiated, positive, negative, atmospheric, frictional, resinous, vitreous.

STATIC ELECTRICITY 5 to 26

Electrical attraction and repulsion — the charge — distribution of the charge — free and bound electricityconductors and insulators — electroscopes — gold leaf electroscope — electric screens' — electrification by induction — nature of the induced charge — the electrophorus— condensers; Ley den jar — electric machines — action of Toepler-Holz machine — Wimshurst machines.

THE ELECTRIC CURRENT 27to34

Volt — ampere — ohm — Ohm's law — production of the electric current — current strength — voltage drop in an electric current.

PRIMARY CELLS 35to67

The word "battery" — action of ceU — chemical changes; polarization — effects of polarization — methods of depolarization — depolarizers — depolarizer bag — Volta's contact law — contact series of metals — laws of chemical action in cell — requirements of a good cell — single and two " fluid cells— the Leclanche cell — Fuller bichromate cell — the Edison cell— Grenet bichromate cell — Daniell celldirections for making a Daniell cell — gravity cells — Daniell gravity cell — so called "dry" cells — points relating to dry cells — care of cells — cleanliness — separating the elements — creeping — amalgamated zinc — battery connections.

TABLE OF CONTENTS; GUIDE NO. I

CONDUCTORS AND INSULATORS - - 68 to 74

The so called "non-conductors" — table of conductors and insulators — mode of transmission — effect of heat — • ,

heating effect of the current — insulators — impregnating compounds — water as a conductor.

RESISTANCE AND CONDUCTIVITY - 75 to 82

Standard of resistance — conductivity of metals and liquids — effect of heat — laws of electrical resistance —

conductivity — specific conductivity— divided circuits.

ELECTRICAL AND MECHANICAL

ENERGY 83 to 92

Definitions: energy, matter, molecule, work, foot pound volt coulomb, ampere hour, power, horse power, watt, kilowatt, watt hour — mechanical equivalent of heat — British thermal unit — electrical horse power — the farad.

EFFECTS OF THE CURRENT - - - - 93 to 104

Thermal effect — use of heat from the current — magnetic effect — chemical effect — electrolysis — electro-chemical series — electric osmose — electric distillation — muscular contractions — electroplating — electrotyping.

MAGNETISM 105 to 124

Two kinds of magnetism — nature of each — poli magnetic field — magnetic force — magnetic circuit — — magnetic flux — the Maxwell — the Gauss — magnetic effect of the current — corkscrew rule — solenoids — permeability — magnetic saturation — magnetomotive forcereluctance — analogy between electric and magnetic circuits — hystereses — residual magnetism.

ELECTROMAGNETIC INDUCTION - - 125 to 180

Faraday's discovery — .Faraday's machine — Faraday's principle — line of force — induction of current — laws of electromagnetic induction — rules for direction of induced current — Fleming's rule— Ampere's rule — the palm rule — self-induction.

TABLE OF CONTENTS; GUIDE NO. I

INDUCTION COILS 137 to 164

Self-induction — mutual induction — primary induction coils — secondary induction coils — plain secondary induction coils — secondary induction coils with vibrator and condenser; cycle of action — magnetic vibrators — vibrator adjustment — table of induction coil dimensions — table of sparking distances in air — points relating to induction coils— wiring diagram.

THE DYNAMO 155 to 160

Operation — essential parts — field magnets — armature — construction of dynamos — -parts; bed plate, field magnets, armature, commutator, brushes.

THE DYNAMO: BASIC PRINCIPLES - 161 to 170

Definitions — essential parts — elementary alternator

— operation — direction of induced current — application of Fleming's rule — cycle of operation — the sine curve; its construction and application.

THE DYNAMO : CURRENT

COMMUTATION 171 to 180

How the current is produced — how direct current is obtained — the commutator — inductors — ' 'continuous current" — action of four coil elementary dynamo — conditions for steadiness of the current.

CLASSES OF DYNAMO 181 to 198

Classification — bipolar and multipolar dynamos — difference between dynamo and magneto — self exciting dynamo — the series dynamo — regulation of series dynamo; difficulties experienced — the shunt dynamo— adaptation — operation — characteristic — regulation — the compound dynamo — service intended for — regulation — over compounding — usual degree of over compounding — short shunt — long shunt — voltage of short and long shunt machines — separately excited dynamos — Dobrowolski three wire dynamo.

TABLE OF CONTENTS; GUIDE NO. 1

FIELD MAGNETS 199 to 220

Object — essential parts — classes of field magnet —

multipolar field magnets — construction — choice of materials — design — pole pieces — eddy current— laminated fields — construction to reduce reluctance of the magnetic tircuit—magnetizing coils — methods of winding — coil ends — insulation — attachment of coils — coil connections . — heating— ventilation.

THE ARMATURE - 221 to 228

Definition — how continuous current is obtained —

type of armature — comparison ring and drum armatures — why drum armature is the prevailing type— disc armatures — why disc armatures were abandoned. '

ARMATURE WINDINGS 229 to 256

Preliminary considerations — winding diagrams and winding tables — lap and wave winding — angular pitch or spread of drum coils — parallel or lap winding — series or wave winding — double windings — Siemens winding — objection to Siemens winding — chord winding — multiplex windings— number of brushes required-^iumber of armature circuits— equalizer rings— drum winding requirements.

THEORY OF THE ARMATURE - - - 257 to 282

Current distribution in ring and drum armatures — connection of brushes — variation of voltage around the commutator — cross magnetization; field distortion — remedies for field distortion — angle of lead — demagnetizing effect of armature reaction — effect of lead — eddy currents; lamination — remedy for eddy currents — magnetic drag on the armature — smooth and slotted armatures — comparison of smooth and slotted armatures — magnetic hysteresis in armature cores — core loss or iron loss — dead turns — friction.

TABLE OF CONTENTS; GUIDE NO. 1

COMMUTATION AND THE

COMMUTATOR 283 to 302

Period of commutation — commutating plane — normal neutral plane — neutral plane — plane of maximum induction —commutation — position of the brushes — sparking-— effect of self-induction — construction of commutators — points relating to commutators — types of commutator.

BRUSHES AND THE BRUSH GEAR - - 303 to 320

Classification — gauze brushes — wire brushes — strip brushes — carbon brushes — adjustment — comparison of copper and carbon brushes — size of brushes — number — contact angle of brush — brush contact— drop in voltage at brushes — brush holders — brush rigging — multipolar brush gear.

ARMATURE CONSTRUCTION - - - 321 to 348

Parts — shaft — core — slotted core-ycore laminations — core bolts — attachment to shaft — insulation of core discs — teeth — ^advantages and defects of slotted armatures — slotted cores; built up construction — ventilation — insulation of core — armature windings — construction of inductors — objection to copper bars — various windings: hand winding — evolute or butterfly winding — connectors — barrel winding — bastard winding — former winding — former coils — peculiarity of evolute coil — "straight out" cod — coil retaining devices — driving horns.

INTRODUCTORY CHAPTER

INTRODUCTORY CHAPTER

The subject matter of this work relates to one of the secrets of creation which appears to have been intended at the very beginning to be "sought out." This idea is expressed in a certain saying copied three or four thousand years ago by the men of Hezekiah, King of Judah: from Solomon's proverbs: "It is the glory of God to conceal a thing: But the glory of Kings (i.e., wise men), to search out a matter"

In all that may be said hereafter through the work, it is admitted that the results recorded are the determinations of experiments performed by an incredible number of searchers extending through many ages. These inquiries have been pursued with a generous rivalry which has permitted discovery to be added to discovery, until the sum total has been wrought into such exactness that it has been thoughtlessly stated that there is nothing more, save its application.

It may be well, however, to state a few fundamental facts relating to electricity: 1, Electricity and magnetism are one and the same thing; 2, what is really known about it has come as a discovery and not as an invention. Thus, we say the intrepid explorer discovered the pole, not that he invented i*

So with electricity it has been a subject of discovery while its many applications to useful purposes have been veritable inven- \ tions; 3, the earth itself is a magnet.

This last is shown by the fact that the earth affects a magnet just as one magnet affects another. Magnets are bodies, either natural or artificial, which have the property of attracting iron, and the power, when freely suspended, of taking a direction toward the poles of the earth. The natural magnet is sometimes called the loadstone. This word is said to be derived from loedan, a Saxon word which signifies to guide. It is an oxide of iron of a peculiar character, found occasionally in beds of iron ore. Though commonly met with in irregular masses only a few inches in diameter, however, loadstones of larger sizes are sometimes found.

By means of simple experiments it may be ascertained that the magnet has the following general properties, viz: 1, power of attraction; 2, power of repulsion; 3, power of communicating magnetism to iron or steel; 4, polarity, or the power of taking a direction toward the poles of the earth; 5, power of inclining itself toward a point below the horizon.

Speaking generally we may say, that magnetism is a department of electrical science which. treats of the properties and effects of the magnet. The same terms are also used to denote the unknown cause of magnetic phenomena, as when we speak of magnetism as excited, imparted, and so on.

Lightning and the Northern Lights are displays of electricity on a grand scale. Electricity is a term derived from the Greek word for amber, that being the substance in which a property t>f the agent now denominated electricity was first Sserved.

INTRODUCTORY CHAPTER

The ancient Greek philosophers were acquainted with the fact that amber, when rubbed, acquired the property of attracting light bodies; hence the effect was denominated electrical and in later times, the term electricity has been used to denote the unknown cause of electrical phenomena, and broadly the science which treats of electrical phenomena and their causes.

Electricity, whatever it jnay prove to be, is not matter nor is it energy \ it is however a means or medium of transmitting energy.

If electricity is to transmit or convey energy along a wire, this energy must be imparted to the electricity from some external source, that is to say, before electricity can perform any work it must be set in motion, against more or less resistance. This involves that pressuremust be applied, and to obtain this pressure, energy must be expended from some external source.

Accordingly, in electrical engineering, the first principle to be grasped is that of energy. Without the expenditure of energy no useful work can be accomplished.

Energy may be defined as the capacity for performing work.

Although electricity is not energy, electricity under pressure is a form of energy spoken of as electrical energy.

In an expenditure of energy in this form, the electricity acts simply as a transmission agent or medium to transmit the energy imparted to it in causing it to flow.

In a similar manner, steam acts as a transmission agent or medium to transmit the heat energy of the coal to the steam engine, where it is converted into mechanical energy.

As just stated, electricity under pressure is a form of energy,- and its generation is simply a transformation of energy from one form into another. Usually, mechanical energy is converted into electrical energy, and a dynamo is employed for effecting: the transformation.

In transforming the mechanical energy of waterfalls into electric energy, this natural power of water due to its weight and motion is first converted into rotary motion by a turbine or water wheel, and then converted into electric energy by a dynamo, or an alternator.

All dynamos are but machines for converting into electric energy the energy which is given to them by some prime mover, as a steam engine, a gas engine, by hydraulic or even by wind power.

All electric motors are merely machines for reconverting the electric energy which they receive by means of the conducting wires or mains, into mechanical energy.

All electric lamps are contrivances for converting into luminous energy a percentage of the electric energy that is supplied through the mains.

Potential and Kinetic Energy. — Potential energy is the capacity for performing work which a body possesses by virtue of its position. Kinetic energy is the capacity for performing work which a body possesses by virtue of its motion.

It must be evident that position or motion given to a body enables it to perform work. In the first instance, for example, a heavy weight at the top of a high tower possesses potential energy. A ten pound weight supported one foot above a plane has ten foot pounds of potential energy.

The flywheel of a steam engine in motion is an example of a body possessing kinetic energy. Some of this kinetic energy which was stored up in the fly wheel during the working stroke is expended in moving the engine over the "dead center/' and any other point where no torque is produced by the pressure on the piston.

Chemical Energy can be converted into electric energy to a limited extent by means of the electric battery, but the cost of this energy is so high that it is commercially feasible only where small quantities are required, and the cost of production is secondary to the convenience of generation, as for signalling purposes, the operation of bells and annunciators, etc.

The chemical energy of coal and other fuels cannot be directly converted into electric energy. For power producing purposes, the

INTRODUCTORY CHAPTER chemical energy of a fuel is first converted into heat by combustion , and the heat thus obtained converted into mechanical energy by some form of heat engine, and the mechanical energy subsequently transformed into electric energy in an electric generator.

Energy cannot be created or destroyed. This is the law known as the conservation of energy which has been built up by Helmholtz, Thomson, Joule and others. It teaches further, that energy can be transmitted from one body to another or transformed in its manifestations.

Energy may be dissipated, that is, converted into a form from which it cannot be recovered, as is the case with the great percentage of heat escaping trom the exhaust nozzle of a locomotive or in the circulating water of a steamship, but the total amount of energy in the universe, it is argued, remains constant and invariable.

Following this law comes the doctrine of the conservation of electricity as announced by Lippman, being undoubtedly the outcome of the ideas of Maxwell and of Faraday as to the nature of electricity. According to their doctrine, electricity cannot be created or destroyed, although its distribution may be altered.

Lippman states that every charge of electricity has an opposite and equal charge somewhere in the universe more or less distributed; that is, the sum of positive charges is always equal to the sum of negative charges*

In altering the distribution of electricity \ we may cause more to appear at one place and less at another, or may change it from the condition of rest to that of motion, or may cause it to spin round in whirlpools or vortices, which themselves can attract or repel other vortices. According to this view all our electrical machines and batteries are merely instruments for altering the distribution of electricity by moving some of it from one place to another, or for causing electricit v. when accumulated or heaped together in one place, to do work in returning to its former distribution.

Electrical engineering has. developed largely and widely within a very short time and its many applications has created so great a demand for various kinds of electrical apparatus, that their manufacture forms one of the leading industries.

Electricity is very valuable as a medium for the transmission of energy, especially to long distances; it is also used to great advantage in lighting, being free from the disagreeable properties of gas or oil.

Again, electricity finds various applications, in extracting gold from the ore, pumping and ventilation of mines, traction, telephone, telegraph, electroplating, therapeutics, etc.

These few, of its many applications will perhaps serve to indicate the far reaching interest and importance of electricity, and possibly help to kindle in the student something of the eagerness in his work and enthusiasm without which he will fail to do justice either to his calling or to himself.

SIGNS AND SYMBOLS

SIGNS AND SYMBOLS

The following signs, symbols and abbreviations are almost universally employed in descriptive and technical works on electrical subjects.

Although, in the arrangement of the Guides, the direct current and alternating current matter has been kept separate, it is perhaps advisable in the case of signs and symbols, to combine those relating to the alternating current with the direct current and other symbols, making a single table, rather than have them scattered throughout the work.

1. Fundamental* h

Length. cm. = centimeter;

in., or "=inch» ft. or ' —

foot. • Mt Mass.' gr. = mass of 1 gramme;

kg.»l kilogramme.

T, /, Time. *— second.

2. Derived Geometric.

S, s, Surface.

E, Volume. a, ft Angle.

3. Derived Mechanical.

v*

Velocity.

Angular velocity.

Momentum.

Acceleration.

Acceleration due to gravity » 82.2 feet per second.

Force.

Work.

Power.

Dyne.

Ergs, ^ft. lb., Foot pound.

I.H.P., Indicated horse power.

E JLP., Electrical horse power.

Of

J.

c,

sc.

Joule's equivalent.

Pressure.

Moment of inertia.

4. Derived Electrostatic.

Pressure difference.

Current.

Resistance.

Santity. pacify Specific inductive capacity.

5. Derived Magnetic.

Strength of pole.

Intensity of magnetization.

Magnetic moment.

Horizontal intensity of earth's

magnetism.

Field intensity.

Magnetic flux.

Magnetic flux density or mag*

netic induction.

Magnetizing force.

Magnetomotive force.

Reluctance, magnetic resist*

ance.

Magnetic permeability.

Magnetic susceptibility.

Reluctivity (specific magnetic

resistance).

6. Derived Electromagnetic.

R, Resistance, ohm.

O, do, megohm.

E, Volt, pressure.

Bin Impressed pressure.

Bo; Eo Active pressuie; ohmic drop.

By ■ Virtual pressure.

Emaz Maximum pressure.

Bay Average pressure,

Eef Effective pressure.

Ef Inductance pressure.

Ec Capacity pressure.

U, Difference of pressure, volt.

I 9 Intensity of current, ampere.

Ifm Impressed current.

la Active current.

It Virtual current.

laas Maximum current

lay Average current.

Ief Effective current. .

Q, Quantity of electricity, ampere hour; coulomb.

C, Capacity, farad.

W, Electric energy, watt hour; Joule.

P, Electric power, watt; kilowatt.

p 9 Resistivity (specific resistance) ohnl centimeter.

G, Conductance, mho.

% Conductivity (specific conductivity).

Y, Admittance, mho.

Z, Impedance, ohm.

X, Reactance, ohm.

Xf Inductance reactance.

Xf Capacity reactance.

B, Susceptance, mho.

L, Inductance (coefficient of Induction), henry.

t% Ratio of electro-magnetic to electrostatic unit of quantity -3 X10 10 centimeters per second approximately.

7. Symbols in general use.

D, Diameter. r. Radius.

/, Temperature.

$ 9 Deflection of galvanometer;

needle.

N, n. Number of anything. x, Circumference •*• diameter »)

per second. 4 Phase angle.

G, Galvanometer.

S, Shunt.

N, n, North pole of a magnet.

S, s, South pole of a magnet.

A.C. Alternating current.

D.C. Direct current.

P.D. Pressure difference.

C.G.S. Centimeter, gramme, Second

system.

B.&S. Brown & Sharpe wire gauge*) B. W.G.Birmingham wire gauge.

R.p.m. Revolutions per minute.

CP. Candle power.

o Incandescent lamp.

— X — »Arc lamp.

Hi|i-

Condenser.

Battery of cells.

Dynamo, or direct cur- j rent motor.

Alternator, or alternat ing current motor.

Converter.

Static transformer.

pnnnv\

' / TnmfV s ^ Inductive resistance.

ELECTRICITY

Chapter I Electricity

Nature and Source of Electricity. — What is electricity? This is a question that is frequently asked, but has not yet been satisfactorily answered. It is a force, subject to control under w^ll known laws.

While the nature and source of electricity still remain a mystery, many things about it have become known, thus, it is positively assured that electricity never manifests itself except when there is some mechanical disturbance in ordinary matter.

The true nature of electricity has not yet been discovered. Many think it a quality inherent in nearly all the substances, and accompanied by a peculiar movement or arrangement of the molecules. Some assume that the phenomena of electricity are due to a peculiar state of strain or tension in the ether which is present everywhere, even in and between the atoms of the most solid bodies. If the latter theory be the true one, and if the atmosphere of the earth be surrounded by the same ether, it may be possible to establish these assumptions as facts.

The most modern supposition regarding this matter, by Maxwell, is that light itself is founded on electricity, and that light waves are merely electro-magnetic waves. The theory "tha*.

electricity ;is related: ;tq, : € <k identical with, the luminiferous ether," has' been* accepted -By the most prominent scientists.

Biit ^hife*efectri(5iiy is*£tSL*a mystery, much is known about the laws governing its phenomena. Man has mastered this mighty force and made it his powerful servant; he can produoc it and use it.

Electricity, it is also conceded, is without weight, and, while it is without doubt, one and the same, it is for convenience sometimes classified according to its motion, as:

1. Static electricity, or electricity at rest;

2. Current electricity, or electricity in motion;

3. Magnetism, or electricity in rotation;

4. Electricity in vibration (radiation).

Other useful divisions are:

1. Positive;

2. Negative electricity;

3. Static;

4. Dynamic electricity.

Static Electricity. — This is a term employed to define electricity produced by friction. It is properly employed in the sense of a static charge which shows itself by the attraction or repulsion between charged bodies.

When static electricity is discharged, it causes more or less of a current, which shows itself by the passage of sparks or a. brush discharge; by a peculiar prickling sensation; by a peculiar ~mell due to its chemical effects; by heating the air or other

"^stances in its path; and sometimes in other ways.

ELECTRICITY 3

Current Electricity. — This may be defined as the quantity of electricity which passes through a conductor in a given time — or, electricity in the act of being discharged, or electricity in motion.

An electric current manifests itself by heating the wire or conductor; by causing a magnetic field around the conductor and by causing chemical changes in a liquid through which it may pass.

Dynamic Electricity. — This term is used to define current electricity to distinguish it from static electricity.

Radiated Electricity. — Electricity in vibration. Where the current oscillates or vibrates back and forth with extreme rapidity, it takes the form of waves which are similar to waves of light.

Positive. electricity. — This term expresses the condition of the point of an electrified body having the higher energy from which it flows to a lo er level. The sign which denotes this phase of electric excitement is +; all electricity is either positive or negative.

Negative Electricity. — This is the reverse condition to the above and is expressed by the sign or symbol—. These two terms are used in the same sense as hot and cold.

NQXE. — In 1749, Benjamin Franklin, observing lightning to possess almost all the properties observable in electric sparks, suggested that the electric action of points, which was discovered by him, might be tried on thunderclouds, and so draw from them a charge of electricity. He proposed, therefore, to fix a pointed iron rod to a high tower, but shortly after succeeded in another way. He sent up a kite during the passing of a storm, and found the wetted string to conduct the electricity to the earth, and to yield abundance of sparks. These he drew from a key tied to the string, a silk ribbon being interposed between his hand and the key for safety. Leyden jars could be charged, and all other electrical effects produced, by the sparks furnished from the clouds. The proof of the identity was complete. The kite experiment was repeated by Romas, who drew from a metallic string sparks 9 feet long. In 1753, Richmann, of St. Petersburg, who was experimenting with a similar apparatus, was struck by a sudden discharge and lolled.

Atmospheric Electricity is the free electricity of the air which is almost always present in the atmosphere. Its exact

cause is unknown.

•

The phenomena of atmospheric electricity are of two kinds; there are the well known manifestations of thunderstorms; and there are the phenomena of continual slight electrification in the air, best observed when the weather is fine; the Aurora constitutes a third branch of the subject.

Pig. 1. — The electric eel. There are several species inhabiting the water, and which hav* the power of producing electric discharges by certain portions of their organism. The best known of these are the Torpidn, the Gyntnotus, and the Silurtis, found in the Nile and the Tiger. The Electric Ray, of which there are three species inhabiting the Mediteranean and Atlantic is provided with an electric organ on the back of its head, as shown in the illustration. This organ consists of laminae composed of polygonal cells to the number of 800 or 1000, or more, supplied with four large bundles of nerve fibres; the under surface of the fish is — , the upper +. In the Surinam eel, the electric organ goes the whole length of the body along both sides. It is able to give a very severe shock, and is a formidable antagonist when it has attained its full length of 5 or 6 feet.

Frictional Electricity is that produced by tie friction of one substance against another.

Resinous Electricity. — The kind of electricity produced upon a resinoois substances such as sealing wax, resin, shellac, rubber or amber when rubbed with wool or fur. Resinous electricity is negative elect' icity.

Vitreous Electricity. — A term applied to the positive eleo tricity developed in a glass rod by rubbing it with silk. This electric charge will attract to itself bits of pith or paper which have been repelled from a rod of sealing wax or other resinous substance which had been rubbed with wool or fur.