First steps in electricity; designed for the entertainment and instruction of young people at home and in school

Front matter

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Prefatory Note

The aim of this book is to describe a number of simple and inexpensive experiments in electricity that can be performed in schools, the lecture-room, and the home circle. None of the experiments are at all difficult or dangerous, nor are the materials, if used with ordinary care, likely to do the slightest harm to furniture or clothing. The aim is also to enable the reader to obtain a general idea of the laws governing the manifestations of this force in nature, and to see how this force is used in the arts, in business, and in manufactures. It is the hope of the author that the book may be of use as a school reader, as a guide to home amusements in science for winter evenings, and as a help to all who wish to get a notion of the general principles underlying the great modern inventions in electricity. Charles Barnard.

New Rochelle, N. Y., March, 1891.

Contents

Chapter I. The First Steps. Asking Questions of Nature. Attraction. Conduction. Grey's Experiment . . . . . . 5-19

II. Frictional Electricity. Conductors. Non-conductors. The Electroscope. Du Fay's Experiment. Insulators. The Dancing Feather. Like Repels— Unlike Attracts, 20-39

" III. Induction. Franklin's Idea. The Egg Experiment. The Electrophorus. The Leyden-Jar 40-59

Chapter I

ASKING QUESTIONS OF NATURE. FRICTION AND ELEC- TRICITY. ATTRACTION AND CONDUCTION.

The afternoon is warm and sultry. There are dazzling mountainous clouds built high in the blue sky. In the west the billowy masses seem duller and take on tints of pale red-in the hazy air. There is a movement among these sierras in the west, and they mount higher and shut out the sun. There are darker shadows below. A vast arch of greenish gray clouds, ragged and torn, creeps up the sky, and behind it is an ashen veil of rain. From the threatening clouds leap flashes of light. Suddenly there seems a more vivid flash and a tall tree is split open and falls to the ground, while terrible peals of crashing thunder fill the air and drown the roar of the wind and the shrill soprano of the rain sweeping through the woods or whitening the water in the river. After the shower has passed we go out and inspect the fallen tree. It is shattered and torn as if struck some terrible blow.

A young girl combing her long hair in a cold room on a frosty morning hears soft crackling sounds in her hair as her comb slips through her tresses.

A woman going out for a walk on a cold day sees some lint on her dress and tries to brush or pull it off and finds that, for some reason, it clings to the fabric. A bit of feather floating near her dress seems to be bewitched and flies through the air and sticks to it as if it were warm wax.

Some children playing with a cat in a dusky room on a winter's night see tiny flashes of light in the cat's fur. Every stroke of affection they bestow on the cat's back is rewarded with a touch of fire.

Here are four curious things you have, perhaps, seen many times. We say they are natural phenomena. What do they mean, are they in any way related to each other? Why did they appear ? Now there are three steps you can take. You can ask some one about them, you can find a book that will tell you some facts concerning them, or you can examine the phenomena for yourself and find out by asking questions of nature. It is a good idea to ask people to ex-

ASKING QUESTIONS OF NATURE. 7

plain things and it is not difficult to sit in a comfortable chair and read a book. It is far pleasanter and every way better to find out for yourself.

All things — plants, animals and inanimate objects, planets, stars, grains of dust in the road and star-dust in the sky — behave in a certain way under certain circumstances. The behavior of anything is the result of some law, and this behavior shows what the law is. A heavy book in the hand, if let fall, drops upon the ground. It behaves in that particular manner because there is a law that it should fall unless supported. The law of gravity caused the book to behave in that way, and its behavior is evidence of the law. Try this again. Try it many times, and the result is the same. We are compelled to think there is a law governing the book's fall.

Take a light feather out of doors in the wind, and let it fall. It floats away, perhaps out of sight, without falling. Here seems to be an exception to the law. Get another feather and try it again in a closed room. It flutters to the floor. There is no exception and we conclude that the feather floating away on the wind behaved in that manner because controlled by some other law that, for the time, was stronger than the law of gravitation.

We have performed an experiment. By means of the book and the feathers we asked questions of nature.

We placed them under certain circumstances, and by watching their behavior, learned something of the laws governing them. We cannot call this hard work, for the experiment was interesting and it was only a pleasure to make it. The search for knowledge of the world by means of experiment is one of the greatest pleasures you can have, and you will find that this method of getting at facts in nature is quite as useful as asking questions of people or reading good books. All that is known of nature and her laws was found out by experiment, by studying the behavior of common things.

Suppose the children, wishing to see the curious sparks on the cat's back at another time, had taken her into a warm, well lighted kitchen, or out of doors on a summer day and then repeated the experiment. They would be disappointed. Not a spark would appear. They would really be repeating the experiment under different circumstances and the result would not be the same. They might imagine that the sparks were made by the cat, but would at once wonder if she did it, why she could not be good enough to let off her little fire- works at one time as well as another. If they were wise children they would not make this mistake, and would conclude that the experiment had been performed under different circumstances and that

ASKING QUESTIONS OF NATURE. 9

therefore the sparks behaved in a different way and refused to appear. Plainly, the children would really begin to learn something about this matter. They would see that the phenomenon appeared only in a cold dark room and not in a warm light one. It is evident that this method of hunting for facts with a common thing like a cat is a very pleasant way of studying nature. The children did not find much, yet it was really something, for they proved that light and heat in some way affected the sparks observed in the cat's fur. They also proved, incidentally, that the cat herself had no hand in this sparking business.

You can study these four phenomena and many others equally curious by simply experimenting or asking questions of nature. It is our plan to now do this by actually performing experiments and by a little reading to try and understand what the experiments mean. All you need is a willingness to learn and patience. Do not be afraid to try many times over. Do everything slowly and thoroughly. Remember always that while nature is dumb, she never makes mistakes. Keep full and complete notes of all you do. Have a pad and stylographic pen handy at all times and record everything you do or see at the time the experiment is made. Shall we now go on ?

For the experiments we are to perform, we need first a suitable time and place, and secondly certain simple tools and apparatus. For all the experiments the best time is the evening and in winter. Cold dry weather is better than warm or damp weather. If the experiments are performed in the daytime choose a sunny day in preference to a cloudy day. The best place is a warm, dry room where there is an open fire. In the daytime select a room with sunny windows. In all the first experiments there must be some means of warming our apparatus, either by placing them before a fire or in the sunshine.

The best table for our work is a common wooden one, and for a cover use brown wrapping paper or place on the table a pine board, smooth and dry. On this board or on the wrapping paper, place all the apparatus used in the experiments. Take particular pains to see that the board and the paper are dry, and to make sure hold them to the fire just before you begin your work.

Next we shall need about a quarter of a yard of good silk — any remnant of dress goods will answer. Cut this into pieces six inches square, and placing one over the other stich them together to form a pad or holder. Pull out or unravel from the silk or from a ribbon or any fabric a few light pieces of yarn or ravellings.

Get also a small piece of loose cotton batting. From the dealer in painters5 materials get a leaf

ASKING QUESTIONS OF NATURE. H

or two of a thin foil (like gold leaf) made of an alloy called Dutch metal. If a leaf cannot be procured, buy a whole " book " which is the name given to a little package of the foil. Next, we need a glass tube of some kind. The chimney of a student lamp will answer : a rod or stout tube about half an inch in diameter and eighteen inches long is much better and and is very cheap. Pull from the cotton batting a couple of little tufts and cut from the Dutch metal foil several pieces half an inch square. See that the glass and the silk are clean, and then, having warmed all these materials before the fire, place them on a dry board on the table.

Nothing whatever happens. None of the things seem to have the slightest influence upon each other. Putting these things close to each other does not produce any change or effect of any kind. Now take the tube and pad to the fire and make them quite hot. Then hold the tube in the right hand, and wrapping the pad about it, with the left rub the pad briskly along the tube for a moment or two. Now, on holding the tube over the things on the board, they behave in the most singular manner. They leap up to meet it and even cling closely to the glass. Take them off and repeat the experiment and they appear more animated than ever. Eepeat the experiment in another way.

12 FIKST STEPS IN ELECTKICITY.

Let one person hold a tuft of cotton in the hand over the head and then drop it. As it floats on the air, let another bring the rubbed tube near it. The cotton behaves in the most surprising manner, leaping through the air to reach the tube.

Eepeat the experiments several times, observing carefully everything that happens. Rest a moment and draw the tube through the hand. Now lay it upon the foil and threads, and nothing happens. Whatever the cause of the singular behavior of these things during our experiments it has now ceased to work and they are no longer drawn to the glass. The effects we observed have completely disappeared. Rub the glass again with the pad, and they all reappear.

We observe that the glass attracts the threads and foil only after it has been rubbed with silk, and that the attraction is but temporary. The rubbing with silk plainly excites this property in the glass, and for convenience, we will say the glass is excited after it has been rubbed by the silk. Excite the glass and try it on other light materials, paper, smoke, an empty egg shell, or on the hair of the head, and make a list of all the things you can procure which are attracted by the glass.

Procure a tumbler of the best quality of glass to be found, wipe it dry and place it upside down on the

ASKING QUESTIONS OF NATURE.

board. Pull a bunch of fine threads (the filling) from a ribbon, twist them together at one end, and place the bunch on top of the tumbler with the loose ends hanging over the side, and lay a cent or other coin on it to keep it in place. Excite the glass and hold it before the threads, taking care to hold the part which has been rubbed opposite the threads. Instantly they will rise and stretch out towards the glass, every little filament standing apart from the others.

Picture No. I. shows how the threads behave when the glass is brought near them. Move the glass about, and the threads follow it as if alive. Brush the glass with the hand and repeat the experiment twice.

14 FIRST STEPS m ELECTRICITY.

We have performed experiments which have been repeated many times for centuries. Long before the Christian era began men observed with wonder that if a substance called electron, and which we now know is yellow amber, be rubbed, that it has this power of attracting light bodies held near it. For centuries this could not be explained, nor can it be fully explained even now. We know nothing more than this : the behavior of these things is due to a certain force in nature which has received the name of electricity. It is easy to see where the name came from when we remember that these experiments were first performed with yellow amber or electron.

It is very difficult to say precisely what electricity is, and for the present we must leave the matter in suspense and wait till further experiments tell us more about it. For convenience we will say that these curious effects are produced by electricity and that we can produce these electrical effects by rubbing or friction. Already you see we have learned something from our experiments. You have discovered that when glass is rubbed with silk the glass is excited to electrical action, and when thus excited or electrified it will produce some very singular effects.

One more experiment. Procure an egg and an egg glass or small wineglass and set the egg upright in the

ATTRACTION. 15

glass. Then get a slender pine stick about a foot long. A yard-stick can be used, if the pine stick is not handy. Carefully balance the stick on top of the egg as in Picture No. II.

Excite the glass and hold it beside the end of the

No. IL

balanced stick, and at once it swings round towards the glass. With a little practice it can be made to follow the glass round and round, clearly showing the stick is attracted by the excited glass.

You have now two facts— electricity can be excited by friction and this electricity has the power of attraction. By doing several experiments you plainly show that there is a law in the matter. Whatever behaves in a certain way every time it is placed in the same conditions we say is subject to a law. In this case we discover there is a law that electricity attracts. You have demonstrated the existence of electrical attraction, and as it repeats itself every time, we say there is a law of electrical attraction.

Having made one step in our work of discovery you can now use the knowledge thus gained to get still more knowledge. Let us use this knowledge to perform other experiments and see what new facts we can learn in regard to the behavior of things under the influence of electricity.

Eub the glass again and hold it over the tufts of ravellings on the tumbler, but quite high, say a yard or more over them. ~No effect. They do not appear to be affected while the glass is at that distance. Eub it and bring it slowly nearer the table, stopping at intervals to see when the attraction begins. It is plain that the electrical attraction does not extend very far from the glass. Try to be exact and make a note of the distance at which the attraction appears to begin.

Now let us try another experiment, using a part of the information you just gained. Get a piece of fine copper wire somewhat longer than the distance at which

CONDUCTION.

you found the things began to be attracted. For instance, if the things began to fly up to the glass when it was six inches above them, make the wire not less than ten inches long. The best plan is to exceed the limit and the wire should be about eighteen inches

No. III.

long. Get a copper two-cent piece and suspend it from one end of the wire by twisting the wire round the coin. Then twist the other end of the wire round the end of the glass tube as shown in Picture No. III.

Carefully holding the tube in the hand rub it with the silk pad close up to the wire while the copper 2 coin is hanging by the wire in the air. Then hold the tube over the tumbler so that the cent on the end of the wire will be over the little bunch of ravellings. At once the threads are attracted towards the metal precisely as in our other experiments it was attracted to the glass. The tube is too far away to influence the threads, and we are obliged to think that in some strange fashion this power of attraction travelled down the wire to the coin and affected the ravellings, causing them to fly up precisely as in one of our other experiments. This is clearly shown in Picture No. III.

Eepeat this experiment with other things and you will plainly see that all the effects of attraction take place near the coin on the end of the wire precisely as when you used the glass rod alone. Who first discovered by experiment that electron had this power of attraction is not known. It was observed by a number of people a long time ago, and yet not one of them seems to have tried to learn more or to have taken the little step in advance that you have just taken. It was not till quite modern times that it was learned that this power of attraction could be made to travel over a wire. Even then it was learned only by experiment. When in 1729 Stephen Grey discovered this curious property of electricity it was probably not known, and certainly was not mentioned in any book. He could

GREY'S EXPERIMENT. 19

not, as people can now, read about it, and only by this very experiment you have just performed was he enabled to make this remarkable discovery. If it had not been known before, you, too, might have made yourself famous by its discovery. Stephen Grey fastened a long linen thread to a glass rod and hung it out the second story window of his house, and discovered that when the tube was rubbed the coin on the end of the thread attracted light substances on the ground below.

A good way to repeat the experiment is to fasten a long fine wire to the glass tube and hang it in the well of a staircase. Let one person hold and rub the tube, and let another go down-stairs and place the ravellings near the copper coin. Take pains that the wire is suspended clear of the stairs and that the experiment is done on a dry day when the glass and silk pad are warm and dry. This property which the copper wire and cent show is called conduction. We say electricity can be conducted and we call the wire a conductor.

CHAPTER IL

THE ELECTROSCOPE. CONDUCTORS AND INSULATORS. DU FAY'S EXPERIMENT. THE DANCING FEATHER. ATTRACTION AND REPULSION.

The experiments you have performed have shown us three things concerning electricity. First it can be excited by friction or rubbing, as when you rubbed the glass tube with the silk pad. Friction caused it to appear and when it appeared we learned that it had the power of attracting light bodies. It attracts everything, but only the small, light materials we used showed it plainly enough for us to see and notice it. It can be conducted through copper, and copper is a conductor of electricity. Observe we have neither seen, heard, nor felt the electricity. We have seen only how it affects certain things and how it behaves when given a conductor. While we could not see it travel down the copper wire, we are very sure it did, because it produced the same effects at one end of the wire as at the other, though the wire might be many yards long. In other words your experiments have shown us the laws of electrical attraction and electrical conduction. Not

THE ELECTKOSCOPE. 21

fully, because there may be much more to learn concerning these laws, but enough to prove that there are such laws.

We also noticed one other thing. When, after any experiment had been performed, the tube was drawn through the hand it lost all power of attraction. We must conclude from this that the power of attraction was not in the glass, because, if it were, why does not the glass always attract ? When the glass is rubbed we say it is excited to electrical action or, in other words, is charged with electricity. When we draw the tube through the hand all the electrical effects disappear, and the inference is that the electricity has in some manner left the glass and disappeared. We, therefore, say it is discharged. What really happens when the tube is discharged in this way is that the hand becomes a conductor and carries the electricity off and it is practically lost — that is, lost as far as our experiments are concerned. To get new effects we must charge the glass over again by means of more friction.

We now need a more convenient method of finding out when anything is charged or discharged and you must construct a more complicated apparatus than any we have used before.

Procure a fruit-jar or wide-mouthed bottle and wipe

FIRST STEPS IN ELECTRICITY.

it clean and dry. Fit a wooden cork to it or place a thin slip of wood on the mouth. Get a short piece of stout copper wire, and bend about one inch of one end at a right angle. Pass it through the wood so that the bent end will hang in the bottle as in Picture No. IV. Eoll

No. IV.

up the other end of the wire into a little knob or ball. Next cut a strip about an inch wide and three inches long from a leaf of the Dutch metal foil we used before, and hang this strip on the bent end of the wire in the jar as shown in Picture No. IV.

This apparatus is called an electroscope, and we shall

THE ELECTROSCOPE. 23

use it in a number of experiments to show the presence of electricity. Eub the tube and hold it over the little knob at the top of the wire, as shown in the picture. At once you will observe a curious effect in the little strip of foil suspended in the jar. The two parts or leaves fly apart. Touch the knob with the finger and they fall together again. We bring the charged tube near the copper wire (conductor) and the leaves fly apart. They are charged with electricity. We touch the wire and discharge it and they fall down again. Why they do this we will not stop to discover. It will be plainly shown by later experiments. Just now we will only notice that an electroscope is an apparatus for showing the presence of electricity, and by its aid we can go on to other experiments.

Make another pad as before, using, instead of silk, common flannel. Then get a stick of sealing-wax, the larger the better, and rub it with the flannel as we rubbed the glass tube with the silk. On holding the sealing wax over the bits of cotton and foil, we find the charged wax has precisely the same properties as the excited tube. We conclude from this that friction between other materials beside silk and glass can excite electrical action and give electrical effects.

You will find it a good plan to repeat all your experiments with the charged sealing wax, because while you get the same results they are not so strong or marked as with the glass tube. From this we find that there may be a difference in the amount of attraction or other effects, though in kind they are alike. Try the wax also with the electroscope.

Having observed that electricity can be obtained from glass and sealing wax, we might go on and find that by friction electricity can be developed from many things. Warm a writing pad of Manilla paper before the fire, and rub the top sheet briskly with the hand, and it will be found that this sheet will be strongly attracted to the one beneath it. Many other things will display the property, and itr is highly probable that all friction excites electricity in a greater or less degree. Electricity obtained by friction for this reason is called frictional electricity.

It is said that some one once brought to Faraday * a

*" Faraday," Michael. (1791-1867). An English chemist, and philosopher. He presents a remarkable instance of the success to be gained over such obstacles as poverty and lack of education, by patience and perseverance. At the age of thirteen he was apprenticed to a book-binder, but employed all of his spare moments in studying science, and in making experiments with implements of his own manufacture. He attended several evening lectures on chemistry, given by Sir Humphrey Davy, and ventured to send to the lecturer himself the notes he prepared on the lectures, which resulted in gaining for him

THE ELECTROSCOPE. 25

new experiment with a request that he would examine the results to be obtained. " Stop a moment," said Faraday, "before you begin, tell me what I am to observe. " So we must learn what to observe. So far we have observed only the attraction caused by the rubbed glass or wax. Eepeat the experiment with the glass tube, silk pad, and bits of foil. The bits of metal leap up to the glass, and then some of them fall back again, and again leap up, perhaps repeating the little flights up and down several times. Here is plainly something else to be observed. Why should the bits of foil behave in that manner? Are they attracted and then repelled? Is the attraction suspended for a few seconds, and then resumed? Clearly there is here a wholly different behavior, and we must infer there is another law governing it. We must find out this law by other experiments. We have already learned that electricity can be conducted through copper. Can it be conducted through other things? You must find

the position of assistant in the Koyal Institution. Later, he accompanied Davy, as amanuensis, on a tour over the continent which lasted a year and a half. Shortly after this he began lecturing, and publishing articles on scientific subjects, and then there began that long, series of important discoveries, accounts of which he gave to the public in volumes, having the subjects arranged according to their position in science.

26 FIRST STEPS IX ELECTRICITY.

an answer to this question before you can solve the others.

Get the glass, silk -pad, the fine copper ivire and the electroscope. Twist one end of the wire round the end of the glass tube as before, and twist the other end round the copper rod of the electroscope. Bub the tube with the silk, and instantly the two leaves of the electroscope start up, rising and falling slightly at every stroke of the rubber. Clearly the electricity developed by friction is conveyed through the copper wire.

We may make this experiment on a large scale by dropping a wire down the well of the stairs, and causing the leaves of the electroscope to be expanded on the first floor by rubbing the glass on the fourth floor.

Next procure about a yard of sewing silk. Tie one end of it to the end of the glass tube (without the wire), and the other end to the copper wire of the electroscope. You may rub the tube as hard as you please and there is no effect in the electroscope. To prevent any mistakes in the matter, use the sealing wax and flannel pad with the silk thread in the same way and the result is still the same. Your experiments prove that there is a difference between the copper wire and the sewing silk. As the little leaves are quiet while the glass or wax is rubbed, though connected by the thread, the inference is that the electricity cannot

NON-CONDUCTORS.

travel through silk as it does through copper. We conclude then that some things do not conduct electricity, and we may call such things own-conductors. Thus with the glass rod and the electroscope you can now make a series of tests with different materials and