Electricity simplified

Front matter

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§1 l"

Chapter I. The Ether — Electricity — Force Axd Energy — Mass And Weight

The Ether — Electricity.

There are in nature certain mysteries, if such a name does not appear too poetical, which have never been solved and may remain so for all future generations. The conservative scientist is apt to include among such things gravitation, electricity, and perhaps light. To explain the phenomena of light, an almost inconceivable entity termed the luminiferous ether has had to be invented. By assuming such a thing to exist and to be endowed with almost inconceivable properties, light is explained and its phenomena are brought into the domain of mathematics. But no direct proof of the existence of the ether has yet been found, and Ave hardly can venture to hope for one.

The modern treatment of electricity deals with it

ELECTRICITY SIMPLIFIED.

as representing and including special phenomena this ether. Some go so far as provisionally to define it as being the ether itself, and to treat static excitement, magnetism, current electricity, etc., as due entirely to different states of the ether.

The luminiferous ether is by calculation deduced as being of the following general properties. It is Bopposed to be a medium most resembling a gas in constitution, yet possessing rigidity like a solid, as well as elasticity like that of a gas. Its density is equal to 930 on e-thou sand- million -mill ion ths (-nnrrfVWu that of water, or equal to that of air at 210 miles above the earth. Its rigidity is one one-thousandmillionth (TooTTuViroo-Tr) that (,} Bteel. It is Bometimes compared to an all-pervading jelly, through which waves of light and other radiant energy and of electromagnetism are constantly throbbing. Particles oi ordinary matter move through it without resistance. It interpenetrates the molecules of matter, and hence an air pump is entirely without effect uj)on it. There is no such thing as an ether vacuum (Daniel). It cannot be excluded from empty space.

Such is the hypothetical luminiferous ether, an ultra-gaseous body possessing the properties of both a solid and of a gas. It should be looked upon as an expedient for the present, as something most useful in formulating theories, but unproved. A theory is often little more than a symmetrical skeleton to sustain our laboriously acquired collection of facts. The

THE ETHER A XI) ELECTRICITY. 11

test of the utility or perfection of a theory is its ability to foretell what will happen under given conditions. It may be able to do this and yet be wholly fictitious.

Light is radiated from one body to another across enormous intervals of space. The mind cannot conceive of one body acting upon another without some connecting medium. The same applies to gravitation and electricity. The ether originally invented to account for the transmission of light through distances, of unknown degrees of immensity in the i ase of the heavenly bodies, has been found a useful factor in formulating a theory of electricity.

If any object is excited electrically, every object within its range of action, that is to say. which is not screened from its effects, is also affected. This involves the same kind of action across a space as obtains in the case of light. It is termed radiant action and is a manifestation of radiant energy. Again, an electric current or the poles of a magnet produce magnetic effects in their vicinity upon objects not in contact with them. This involves action at a distance also.

These are among the reasons which have induced scientists to invoke the luminiferous ether to aid in explaining and accounting for electrical phenomena. As employed in the present work it will be found useful in enabling the mind to better formulate a theory of the science. Extraordinary as the idea of the ether may appear, it is evident that the modern achievements of electricity are just as strange. They are of such nature as to be entitled to an extraordinary line of explanation.

The sun is at such a distance from the earth that it takes light over eight minutes to travel from its surface hither. The nearest of the fixed stars are so remote that in many cases days and years are consumed in the passage of light from them tons. If one of these bodies were suddenly annihilated we should see its light after it ceased to exist. The sun would seem to continue to shine for eight minutes and twenty seconds after its extinction. We may even now seem to see stars which Long ago ceased to be luminous, and distant suns may now be radiating light into space, which light will not reach us to show us a new star, for years to come.

All this is so strange and deals with such infinite relations of quantities as regards distances and time that the luminiferons ether, viewed from such a standpoint, seems not too extravagant a conception to account for the high velocity and intensity of radiant energy.

Pulses or waves of electric energy are found to act like light, to be capable of transmission through some bodies, of reflection from others, and of refraction and interference. The relations between electrostatic and electromagnetic units indicates a ratio corresponding to the velocity of light. These considerations give

RADIAN 7 ENERGY. 13

direct ground for utilizing the theoretical ether as a medium for the propagation of electrical disturbances.

The term radiant energy is continually acquiring new scope in physics. Many phases of electrical disturbance fall under this heading. Others may be attributed to radiant force.

The passion for unification at one time tended to obliterate the old distinction between static and dynamic electricity. Now a true basis for such division must be recognized and may to a certain extent be determined by the consideration of force and energy. Trjie static phenomena are phenomena of ether stress or of force; electromagnetic wave and current phenomena are related to ether waves or energy.

Force, Energy, Mass, and Weight,

Physical concepts, such as force, mass, energy, and other elementary things, have received within recent years much accuracy and definition of description and attributes. Only a few years ago great confusion existed, notably in the distinction between force and energy. The enunciation of the absurd doctrine of the conservation of force, and its support in many essays and papers by those who were assumed to be the leading thinkers of the day, is an illustration, now but a few years old, of this fact.

This accuracy has led, and is leading, to more and more subdivisions, which brings about a multiplication of units, and increase in nomenclature especially in electricity, which has already been felt to be a misfortune, although it is not easy to see how it is to be avoided.

For the purposes of this work it is quite unne< sary to enter into all of these subdivisions. There are a few elementary mechanical ideas which may be enunciated before the electrical part is entered on, These involve subjects which are often sources of error and misunderstanding.

As physics and mechanics are based upon measurement, units of different kinds have been established. They are based upon length, time, and weight. The relations of these factors to the compound units are termed the dimensions of the unit. The centimetre, gram, and second are the bases of measurement, and the fundamental units constructed or built up upon them are termed the centimetre-gram-second or C. G. S. units.

Force is that which, acting on a quantity oi matter or mass, can change its rate of motion or can impart motion to it. It can be called into existence or annihilated under adequate conditions; in other words, there is no conservation of force. Its unit is that force which can in one second impart to one gram of matter a velocity of one centimetre per second. This unit is termed the dyne. The weight of one gram is equal to about 981 dynes. A dyne ia equal to about G3^ grains.

FORCE AND ENERGY. 15

The exertion of force along a path in space, which condition necessarily implies motion against resistance, is termed work. Its unit is a dyne exerted through a path one centimetre long. The most convenient way to express force is to refer it to gravitation. Hence the unit of work is generally defined as the raising of ^- f gram to a height of one centimeter against gravitation* The name of the unit is the erg.

The power of doing work is termed energy. A weight of g-| T gram by frictionless machinery could, in descending one centimeter, raise another body of the same weight the same distance. Hence it would be said to possess energy of position, a form of potential energy, equal to one erg. The sum of energy in the universe is invariable; energy can be neither created nor annihilated by natural causes. This is the doctrine of the conservation of energy, which has replaced the discarded one of the conservation of force.

If a bullet is fired from a gun, the energy of the combustion of the powder is in part expended in driving the bullet forward ; in part in driving the gun backward, producing recoil; in part in heating the gun and bullet, and in various other ways. None of its energy is destroyed. The bullet strikes a target and is brought to rest. Its energy is not destroyed, it is only transformed. Some appears as heat energy — indeed most of it directly or indirectly takes this form: none disappears.

If this doctrine is true, perpetual motion against resistance, as generally understood, is impossible. There is very little doubt of this doctrine's truth.

It follows from the above that energy cannot, properly speaking, be expended, and that work is not done at the expense of energy. Work simply denotes the reciprocal of a given form of energy, and is produced by the disappearance of that particular form of energy, and is the result of its conversion into some other form. A weight raised by the combustion of coal is the reciprocal of the heat energy, and no more represents work than it does the product or the result of the conversion of heat energy into mechanical potential energy. In other words, work and energy may be treated as identical. To do work, energy is required, and is absorbed in the process by being converted into some other form or forms. The other forms, either one or more of them, are in many cases some irreclaimable form or forms, which can never again be utilized. This is so often the case that the available energy of the universe is undoubtedly tending to zero. This zero will be attained when all objects have the same temperature.

A body placed at a height above a plane possesses what is termed potential energy, referred to the plane. Its advantageous position indicates a power of doing work. Another example of potential energy would be a strained spring, possessing the energy of stress.

ENERGY AND MASS. 17

A body in motion, by virtue of its inertia or resistance to reduction of velocity, can do work, and is said to possess kinetic energy. A body at rest in a certain sense may be said to possess the same with reference to moving bodies, because all rest and motion are relative.

An example of the transformation of energy can be taken from the above. A one-pound weight raised one hundred feet has expended upon it one hundred foot-pounds of energy, and possesses that amount of potential energy. If now it is allowed to fall through the same distance, it parts with its potential and assumes kinetic energy. When it has fallen one hundred feet, if in a vacuum, it will at the one-hundred foot mark possess none of its original potential energy, but in its place will have one hundred foot-pounds of kinetic energy. As it strikes the ground and comes to rest, this energy will change into heat energy and other forms, but it will remain the same in amount — one hundred foot-pounds.

Mass is the quantity of any portion of matter. Owing to centrifugal force a body weighs less at the equator than at the North Pole; upon the surface of the moon it would weigh far less. Yet its mass would be the same although its weight might vary. Were transportation cheap enough, and were the other conditions favorable, a merchant could make money by selling by weight, in northern or southern latitudes, goods which he had purchased by weight in equatorial latitudes, provided, he weighed with a spring-balance. He would buy and sell the same weight, but would buy a greater mass than he sold.

Weight is mass acted on by gravity. As gravity varies, weight will vary, even though the mass remains the same: all which has been just illustrated.

In electricity we have force and energy. Heat energy in driving an engine that drives a dynamo becomes ultimately converted into electric energy. An electric machine or a battery on open circuit maintains its terminals at a varying potential, or in such state as to exercise electromotive force. This force, producing a current through a resistance, does work. As for electric mass and weight, a3 yet they are not recognizable, and probably do not exist.

Chapter II

THE ELECTRIC CHARGE — POTENTIAL— THE DIELEC- TRIC — POSITIVE AND NEGATIVE ELECTRICITY — CONTACT ACTION— ELECTROSTATIC LINES OF

J FORCE— THE LEYDEN JAR.

The Electric Charge, Potential, and Dielectric.

The first idea of electricity is that we are able to place bodies in different electrical relations. A stick of sealing-wax or the amber mouthpiece of a pipe rubbed upon the coat sleeve will attract bits of paper, or will draw around with it, magnet-like, a walking-stick suspended by a thread tied around its centre. The very name electricity is derived from the Greek name for amber.

The sealing-wax or amber in the above case is said to be charged with electricity, and represents the form of electric force already spoken of. It is useless to attempt to determine what the electricity is whose presence so alters the condition of the body. It is usually taken as an entity of some kind, and in old times was termed and now is often termed colloquially a fluid, although it is certain that it is no such thing.

A body electrically charged is most simply treated as one whose surface is surcharged or undercharged with electricity. By an electric machine based upon contact action, by a galvanic battery, or by other means, electricity can be altered in its distribution. The action is analogous to that of a pump which pumps water from one reservoir into another, both originally of equal level. Thus we may imagine two reservoirs of similar level of water. If water is pumped out of one and into the other, they are brought into such relation that, if any chance was given, the water would flow from one to another, and the original level would be reached again. If for these reservoirs we substitute bodies insulated from any supply of electricity, we can by an electric generator, which we may term an electric pump, abstract electricity from one and add it to the other. Both bodies are then said to be charged, one positively, the other negatively. As in the case of the reservoirs of water, if any chance was given, electricity would flow from one to the other, and the original state of tilings would be re-established.

The electric charge resides entirely upon the surface; the cubic contents of the body has nothing to do with it. Again as regards a specific surface, there is no limit to the electricity which can be charged upon it, provided it can, so to say, be held there. By a physical metaphor, the elasticity of electricity seems to be perfect and indefinite.

POTENTIAL DIFFERENCE. 21

This gives the idea of an electric charge. Returning to our reservoirs of uneven level or " charged," if they were connected the original level would be attained, and more quickly or slowly in proportion to their difference of level. The greater this difference, the greater will be the tendency to return to the original level. The same applies to the electric charge. The greater the difference of charge, the greater will be the tendency toward partial equalization. This difference of charge is termed difference of potential, or potential difference, or electromotive force, and the terms high or low potential in a system indicate a large or small difference of charge of different parts.

The levels of water in the reservoirs, instead of being compared with each other, might be referred to that of an ocean of constant level. Water might be pumped from one into the ocean, or from the ocean into one or the other, or both, so as to affect their level, with respect to such an ocean of constant height. Electricity can be treated in like manner. It can be pumped from the ocean of electricity, which the earth represents, or the same earth can be used as a recipient of charges pumped from other bodies. Any of our reservoirs put into communication with the ocean would at once begin to attain the same level. Any charged electrical body put into communication with the earth, will in a short time, w T hich may be an infinitesimal fraction of a second, be reduced to the standard potential of the earth, which by convention has been taken as zero potential, just as in stating elevations of the earth's surface the height of the water of the sea is made the basis or zero of height.

The fact that, other things being equal, the capacity of a body for holding" a charge of electricity depends upon the area of its surface is shown in a familiar experiment. If a piece of tinfoil or other conducting material is charged, and is then rolled up, thus reducing its area, the charge shows a higher tension or desire to escape. It is to a certain extent as if the area of one of our reservoirs was in some way diminished. The water would rise in height and acquire a greater pressure. This experiment also proves very clearly the fact that an electric charge resides upon the surface.

Small drops of water charged with electricity, if they unite to form larger ones, will present a smaller total surface, and hence will raise the potential of their charge. This is supposed to be one of the causes of the electric disturbances in thunder showers, where the electric charge of the atmosphere seems to increase in potential enormously.

The reservoirs, if to be filled or partly emptied, must have walls of some strength. If of the level of the ocean, their walls maybe of zero strength for they will be supported outside by the ocean water which we may assume to penetrate the soil. To enable the surface of objects to hold an electric charge, they

THE DIELECTRIC. 23

must be surrounded by something to retain it. This substance or entity that holds a charge, upon a surface, which substance or entity represents the walls of the reservoirs, is termed the dielectric. It may be the air or any of the non-conductors of electricity. Even a vacuum is a dielectric almost equal to air. This fact is generally expressed by stating that the ether is a dielectric.

If connected by a pipe, the reservoirs will discharge one into the other and assume the same level. If two electrically charged bodies are connected by a piece of metal such as a wire, they will at once assume the same potential. The wire is termed a conductor. All metals and many other substances conduct electricity so well as to be termed conductors. Others conduct it so badly as to be termed insulators. The latter are all capable of acting as dielectrics.

If the air was a conductor, a surface could never be excited or charged in it, there could be no thunder storms, and man would probably have never known anything about electricity unless from animal sources such as the torpedo and gymnotus. Water containing salt in solution is a conductor. Hence there are no electric storms or disturbances in the ocean and its inhabitants only experience animal electricity, but never that from any other source.

The dielectric is the opposite of a conductor, Anything that is not a conductor may act as a dielectric.

Formerly no distinction was drawn between it and an insulator. Now any insulator that surrounds a charged body, whether that insulator be glass, India rubber, gutta-percha, air, or a vacuum, is called a dielectric.

As the charge is to be held upon a surface, and not within a body, it is evident that for quick charging the surface must be conducting. Sealing-wax, amber, and glass, for instance, are non-conducting, and receive a charge only with difficulty, and part with it also with difficulty. If coated with tinfoil, goldleaf, or some thin metallic coating, they become much easier to charge, although their capacity remains unchanged.

This question of capacity is affected by two things, the area of the surface and the nature of the dielectric. The capacity of a system of two conductors and an intervening dielectric, called a condenser, is the quantity of electricity it can retain at a given potential. A typical form consists of two pieces of tinfoil with a sheet of gutta-percha, mica, or paper dipped in paraffin, between them. It is charged by passing or introducing opposite kinds of electricity into the two sheets of foil. As this is done the potential difference between the tinfoil layers rises, more rapidly as the surfaces are smaller, and this potential rise varies also very curiously with the nature of the dielectric. This difference between dielectrics depends on specific inductive capacity.

CONSERVATION OF ELECTRICITY. 25

Positive and Negative Electricity.

A zero of potential being accepted, arbitrarily taken as that of the earth, it is found that bodies can be excited so as to bear opposite relations not only to each other but also to the earth. This at once establishes the idea of positive and negative electrical excitation, and of positive and negative charges. It is found that if a piece of glass is rubbed against a piece of amber they will become oppositely excited. As a matter of convention, the glassy or vitreous electricity is called positive, and the resinous electricity is called negative.

One body cannot be charged with a quantity of positive electricity without an equal charge of negative ekctricity being established somewhere else, and vice versa. The algebraic sum of equal positive and negative quantities being zero, the sum of all electrical charges in the universe is zero. This doctrine is comparable to the law of the conservation of energy, in the sense that the sum is constant, and it has been termed the law of the conservation of electricity.

If copper and zinc are brought into contact and are separated, the copper is charged with negative, the zinc with positive, electricity.

If the copper and zinc be immersed in acid which acts most strongly upon the zinc, the distribution is different : the zinc is negatively, the copper is positively, charged. This is the case in a galvanic battery.

ELECTRICITY SIMPLIFIED.

This question of positive and negative gives the of convention for fixing the direction current is assumed to be the discharge of positive upon negative. If negative electricity is poured into a body it adapts that body to receive a positive charge of equal value.

All this is conventional; it is merely a necessity of the case. Some assumed direction of current and nomenclature of excitation is required.

It will be observed that the relative conditions of zinc and copper are opposite when immersed in arid or when separated from contact. This is because when immersed in acid the excitation or charge is derived from the separation of the constituents of the water in which the acid is present. The hydrogen with its positive charge travels to the copper; the other constituent atom of the water, or radical of the acid molecule, it may be, travels with its negative charge to the zinc. This negative charge it pours into it, or rather discharges it upon its surface, thereby adapting it to receive an opposite and equal charge of positive electricity from the copper.

'According to Franklin's views, who treated electricity as a single fluid, the positive charge consists in an excess and the negative charge in a deficiency of electricity. Hence in the above illustration the zinc becoming negatively charged merely means that it loses a part of its total quantity of electricity. This carries out the idea of the direction of a current.

SINGLE AND DOUBLE FLUID THEORIES 27

The overflowing or positively charged body, namely the copper, sends a current, if permitted, into the partly exhausted or negatively charged body.

Therefore, according to the single-fluid theory, a charge indicates an excess or deficiency according as it is positive or negative. It carries out well the theory of the conservation of electricity.

The double-fluid theory assumed that there were two fluids, one positive and one negative, neutralizing each other in equal quantities.

Now both these theories are discarded almost entirely. It is convenient as an analogy, however, to treat of electricity as a fluid in some of its manifestations, and simplicity will be gained and the truth more nearly approximated to by using the single-fluid hypothesis where it gives a useful analogy.

The charge, positive or negative, is really the keynote of all electrical phenomena. All that we know of electricity are the manifestations due to charges held upon surfaces and intermittently discharged, which is static electricity; or to charges continuously supplied and discharged along conductors, which is kinetic or dynamic electricity. The methods of producing these charges are by contact action and induction. To the first may be referred so-called frictional machines and also batteries.

The relations of bodies oppositely charged in general are that the opposite electricities tend to combine. Bodies oppositely charged, therefore, attract each other. Under certain conditions they can impart their opposite charges to each other and then are no longer attracted.

The bodies excited oppositely as described and attracted cannot impart their charges one to the other through space, except where a conductor connects them, or, if not, where the charges are of high enough potential difference in relation to the space separating them and to the substance filling it. In that case they may discharge by a violent action producing a spark and noise. This disruptive discharge is seen in the lightning stroke.

If the excited bodies are brought into contact, they will adhere, because the opposite electricities tend to combine. This adhesion, when satisfied, represents the disappearance of a specific form of energy. As energy cannot be annihilated, this specific form must be converted into some other, which other form is heat energy. The heat of combination of dissimilar metals, or of other substances, usually in the order of chemical energy and affinity, is also in the order of electrical energy. This correlates chemistry and electricity.

If, instead of bringing the bodies in contact with each other, they are connected by a metallic rod, their relative excitement disappears as long as they are thus connected. The rod acts to provide a path for the electricity and, as we have seen, is called a conductor. The electricity passing by the path thus opened

CONTACT ACTION. 29

for it is termed a current. If one of the bodies is drawn away from the conductor, it has a charge proportioned to the difference of electrical character between itself and the conductor.

Just as the like poles of magnets repel each other, so two bodies excited with like qualities of electricity repel each other.

If an excited body, for instance one with a positive charge, is brought near an indifferent or uncharged body, it attracts it. This it does by attracting to the part of such body nearest it the opposite or negative electricity. This it attracts by attracting the body itself. If negatively excited, it also attracts by drawing the positive electricity of the body toward itself, and hence drawing the body as before.

Contact Action and Electrostatic Lines of Force.

Imagine two bodies of identical substance placed near together. A slight attraction will be exerted by each upon the other, which is termed the attraction of gravitation. Touch and separate them and the attraction will remain the same, and will vary, if they are small enough, in a certain proportion to their distance apart; if of small enough relative dimensions, with the square of such distance. Next assume two bodies of dissimilar nature placed near together. They will be attracted by mutual gravitation. Xow touch them, best by rubbing to secure good contact, ^nd separate them, and they will exhibit a strong attraction for each other. Under ordinary conditions this attraction will be vastly more than that of gravitation. A piece of sealing-wax rubbed against the coat sleeve will attract the sleeve. The contact acts to establish bonds of attraction that operate like India-rubber bands, pulling the two objects together. The objects are then said to be electrically excited. In this excitement and attraction not only the bodies but the intervening ether is thought to be concerned. The ether is supposed to be so stressed as to represent or act like connecting India-rubber bands, and to pull the bodies together. The same applies to a magnet and its armature. The magnet throws the ether into an analogous state of stress. As its armature is brought near it, this stress is affected by its proximity, and acts to draw magnet and armature together. As the stress is easiest pictured as connecting lines, and as these lines indicate the exercise of force, they are termed lines of force, the first electrostatic lines, the others electromagnetic lines.