A popular exposition of electricity with sketches of some of its discoveries

Preface

The recent extraordinary progress of electricity, its stimulus to commerce, and its mysterious possibilities, make it, par excellence^ the science of sciences of our day. All should be familiar with its essential principles at least.

Many learned and excellent treatises have been devoted to the subject, but so illustrated with complex and intricate mechanical diagrams as to frighten away the timid and uninitiated.

My sole aim in this little book is simplicity. ' The mechanical part of the science is continually changing; new patents are being daily issued, so that a thorough and full description of the multiplex machinery, except for a professional, would be time wasted. I have, therefore, devoted my

4 PREFACE.

care almost entirely to the explanation of principles, to the exclusion of mechanics.

I consider, moreover, that complicated diagrams, by drawing away the mind from the subject-matter in hand, confuse rather than simplify.

I have aimed throughout at manifesting the identity of all the forms of electricity, and have accordingly so arranged the matter that each succeeding form naturally flows from its predecessor.

I have also given short sketches of the men who have added most to the science by their great discoveries, and placed the man as closely as possible to his work.

Women should be especially interested in electricity. It is woman's science. A woman was the discoverer of its dynamic branch. The wife of Galvani, the bright daughter of the eminent Galeazzi, is the initial link in the golden chain of illustrious discoverers who have given to us the modern science of electro-dymanics.

Contents

CHAPTER PAGE

I. — Magnetism 7

II. — The Mariner's Compass 18

Chapter I. Magnetism

Electricity, under the form of magnetism, seems to have been both recognized and utilized by mankind from all antiquity. There is a dim tradition that the magnetic chariot, tehi nan, was used in a rude form by the Chinese as far back as the reign of the Emperor Hoangti, twenty -six hundred years before our era. A wagon of this kind, to guide the traveler over the great wastes of Asia, was certainly in use eleven hundred years before Christianity.

In this apparatus a freely floating needle moved the arm and hand of a small figure, which pointed toward the south. This wagon was in use in Asia down to the fifteenth century.

The magnetic needle was unknown in Europe prior to the eleventh or twelfth century. William Gilbert, of Colchester, born in 1540, was the first to write a regular treatise on magnetism and reduce the subject to a scientific basis. According to his testimony, Marco Polo was the first European who applied the magnetic needle to the purposes of navigation. This he did in returning to Europe from the East Indies, in the year 1260. According to other and more probable testimony, however, the magnetic needle was known in European seas some seventy years previously.

Magnetism is derived from Magnesia, a town of Lydia, in Asia. An ore of iron, called lodestone, has the property of attracting to itself small particles of iron, cobalt, and nickel ; and as this ore was found in great abundance in Magnesia, it was called by Pliny magnes, and hence magnet.

Lodestone is the magnetic oxide of iron, Fe a 4 , and is a union of the protoxide and sesquioxide of iron. The scales thrown off under the smith's hammer are this oxide.

Lodestone, mounted in a soft-iron frame, constituted the original magnet.

Magnets are natural, artificial, and permanent. The magnetic ore of iron is the natural magnet.

MAGNETISM.

Steel or hardened iron, when brought into contact with a magnet, becomes magnetized, and is called an artificial magnet. Soft iron is magnetic only when in contact with a magnet, and, when parted from the magnet, at once loses the magnetic property.

Hardened steel, once magnetized, never loses its magnetism, and hence is called a permanent magnet.

When a small magnetic steel bar is freely suspended on a pivot, it will so arrange itself that one end will point toward the north, and the other end, by consequence, toward the south ; and, however the bar be moved thereafter, it will invariably, the disturbing force being withdrawn, restore itself to this position, the same end as before pointing north, and the same south. This is the most obvious property of a magnet, and is called polarity.

The needle of the compass is simply a magnetized piece of steel, balanced upon a pivot, and placed in a box having a circular card, divided into thirty-two equal parts. The end pointing north is called the north pole of the magnet, and the end pointing south, the south pole. The unlike poles of two magnets attract each other, while similar poles repel ; that is, a north pole will attract a south pole and repel a north pole, and a south pole will repel a south pole and attract a north pole.

"When a piece of soft iron is brought into contact with a permanent magnet, the soft iron will itself become magnetic, and, while in connection with the magnet, will attract other smaller pieces of metal. This process is called induction, for the magnet induces its own magnetic property in the soft iron. The soft iron, however, loses its magnetism immediately on the withdrawal of the magnet. A magnet will induce magnetism in soft-iron filings in its immediate vicinity, although not in actual contact. Magnets, natural or artificial, can induce by touch permanent magnetism in a rod of steel or hardened iron.

When one of the poles of a magnet touches the end of a soft-iron rod, that portion of the rod in contact with the pole will assume the opposite magnetism to that of the pole; the positive pole inducing negative magnetism, and the negative pole positive magnetism. The magnetism of the other extremity of the rod will be similar to that of the pole.

If the pole of a magnet touches the center of an iron bar, the magnetic fluid of the center will be opposite, and that of both ends of the bar will be similar to that of the pole. If either pole be brought in contact with the center of a circular plate of iron, the center will have opposite and the rim similar magnetism to that of the pole.

If a bar-magnet be broken in the center, the pieces, instead of having all positive or all negative, will each have both positive and negative polarity, so that neither can ever be entirely eliminated, or parted from the other.

The generally accepted theory of magnetism is that, in any body capable of being magnetized, such, for instance, as a bar of iron, there exist two fluids, one called the boreal, northern, or positive ; and the other the austral, southern, or negative. These fluids, in an ordinary piece of soft iron, are combined together, and so are in the latent state. When the iron becomes magnetized, these fluids are set free, one rushing to one and the other to the other extremity of the bar. Every atom or molecule of iron contains both these fluids, and can never part with them ; the only change occurring is the decomposition of the fluids into their separate elements. In a permanent magnet the fluids are disunited in each and every single molecule, the positive fluid ranging itself on one side of the molecule and the negative on the other. The positive of each atom throughout the bar neutralizes or disguises the negative of its neighboring atom, excepting the positive and negative of the atoms at the extreme ends. Thus, the fluids of one side of the two extreme atoms are free, the positive fluid constituting the positive pole, and the negative fluid the negative pole of the magnet. This explains the reason why the central portion of a magnet has no magnetic properties, the positive fluid of each particle disguising the negative fluid of its neighbor. Hence, also, a magnet in the form of a ring gives no evidence of free magnetism, but, being broken, the fragments will be found to be highly magnetic.

The process of induction in soft iron is explained in a similar manner. When a rod of soft iron is approached toward the negative pole of a magnet, the fluids of the atom in immediate proximity to this pole are separated, the positive being forced to the side nearest the magnet, and the negative to the other side. This last negative holds the positive of the second atom, sending its negative to the opposite side, and so on, until the last atom is reached, and its positive is disguised by the preceding atom's negative and its own negative is set free. The magnet being removed, the fluids are recombined, and the rod loses its polarity.

Another theory, more complex, much in vogue, however, and very ingenious, is Ampere's. According to Ampere, currents of electricity are incessantly running around every particular molecule of a magnet. The resultant of these small currents produces a great current circling the magnetic bar. The difference between a magnet and an ordinary rod of iron is, that in the latter the electricity is latent, and in the former in an active state of motion.

The harder and more dense the steel, the more difficult it is to be magnetized, but the more permanent the magnet. It would appear that the closeness of the molecules offers a mechanical impediment to the free movement of the imponderable magnetic fluids.

Hitherto only iron, cobalt, and nickel have been mentioned as sensitive to magnetic influence, but Faraday by his experiments discovered many other substances susceptible of polarity. Manganese, chromium, cerium, titanium, palladium, platinum, osmium, and arsenic, with their salts and even solutions, are thus susceptible.

Dr. Faraday by his brilliant researches, besides adding greatly to the development of electric science in general, did more than any other man to demonstrate the identity of magnetism and electricity.

The process by which a piece of steel is converted into a magnet is technically called a " touch" There are many kinds of touches. The single touch is the simplest mode of generating magnetism in a steel rod. This is accomplished by running one pole of a magnet several times over the bar to be magnetized, always, however, in the same direction. The end of the bar last touched by the positive pole of the magnet will become a negative pole.

Magnets are commonly shaped like the letter U, and have received the name of horseshoe magnets. Several of these magnets are sometimes joined together, and thus form a very powerful one, or rather a battery of magnets. Magnetism exists entirely on the surface, so that a magnetic hollow cyclinder will be equally powerful as if it were solid. A number of small magnets connected together have more power than the same weight of metal in a single magnet, because they present more surface. Rust, grinding, filing, weaken the power of a magnet, showing magnetism to have more to do with the surface than the interior.

When magnets are ]eft to themselves, they constantly, though very slowly, lose their magnetism. To prevent this loss, a piece of soft iron, called the armature, is placed across the poles. The armature, becoming magnetic, seems to react upon the magnet, and thus not only to conserve its magnetism, but really to increase its intensity. Small weights suspended from the armature, and occasionally increased, will increase the strength of the magnet to a certain limit. Thus, a one-pound magnet can be made to lift a weight of twenty-eight pounds.

The attractive force of a magnet is diminished by raising its temperature. A magnet heated slightly loses a portion of its power, but regains it again upon cooling. When heated to redness, it loses its polarity completely, and does not recover it upon cooling. On the contrary, a decrease of temperature increases the magnetic force.

Coulomb, with a torsion-balance, has found that the force of magnetic attraction is inversely as the square of the distance, which is the law governing the intensities of heat, light, and gravitation.

A bar of soft iron, when acted upon by a magnet, is equally attracted by both poles, and when such a bar is freely suspended over the poles of a horseshoe magnet, it will so arrange itself as to be in the line of the magnetic force — that is, in the direction of a line connecting the poles.

Dr. Faraday found that certain bodies, when approached by a magnet, were repelled by both poles ; and bars of such substances, when freely suspended over the poles of a magnet, arranged themselves at right angles to the direction of the magnetic force. All bodies attracted by a magnet, however feebly, are called magnetic, and those repelled diamagnetic.

The principal diamagnetic substances, in the * order of susceptibility, are bismuth, antimony, zinc, V' tin, cadmium, mercury, silver, copper.

Animal flesh has been found to be diamagnetic, and a man suspended freely in a horizontal position over the poles of a powerful magnet would be repelled by both poles, until he pointed due east and west, the direction of the poles of the magnet being north and south.

One of the most splendid discoveries of Faraday was that the oxygen of the air is magnetic. This property of oxygen must, consequently, be an element in the explanation of the origin of electric storms and of the aurora borealis. The earth itself is considered a great magnet. Gauss estimates its magnetic force to be as great as if every cubic yard of it contained six one-pound magnets.

According to Ampere the magnetism of the earth is occasioned by electric currents constantly circling it from east to west in spiral lines. These currents are caused -by the sun's rays. These spirals induce in the earth a magnetic axis at right angles to themselves, and whose poles nearly coincide with the earth's geographical poles.

Both natural and artificial magnets owe their polarity to induction from the earth. Tools in workshops, placed vertically, become magnetized A bar of iron, placed in the magnetic meridian, and inclined at an angle corresponding to the dip of the needle for the locality, will become magnetic. Sunlight has a magnetic effect on steel; and needles, placed in glass bottles of a violet or blue color, will become magnets.

Great advances have been made within a very short period in this beautiful science of magnetism, and yet we have but touched the shores of this enchanting wonderland.

:J

CHAPTEK II.

THE MARINER'S COMPASS.

The present mariner's compass is a delicate piece of mechanism. It consists of a long, flat lozenge-shaped magnetized needle, balanced horizontally on a very fine point of some hard substance. Everything possible is done to eliminate friction. The center of gravity of the needle is pierced, and a piece of agate inserted to rest on the point of a steel pin. Beneath the needle and attached to it, so that they move together, is a circular card divided into thirty-two parts, called points. The extremities of the needle point to two divisions of the card diametrically opposite, which are marked IT. and S., and correspond to the north and south poles of the needle. The extremities of the diameter running across the card at right angles to the needle are marked E. and W.

The whole circle of 360° is divided into thirty-

THE MARINER'S COMPASS. 19

two points, so that each point consists of 11° 15'. Between the N. and the E., for instance, there are eight points, marked respectively N. by E., K K E., K E. by K, K E., K E. by E., E. N. E., E. by K, and E.

The other quadrants are similarly divided. To prevent the compass from being thrown out of a horizontal position by the rolling of the ship, it is attached to a pair of circular brass hoops or gimbals. The outer hoop is firmly fixed to a stationary object, and the inner one is attached to the outer by two pivots at the extremities of a diameter in such a way as to allow it free motion within the outer hoop. The compass-box is attached to the inner hoop by two other pivots at the extremities of a diameter at right angles to tfie first diameter. In this way the compass may move freely in two directions at right angles to one another, and thus its horizontal position is secured under any and all circumstances.

In the box containing the compass is a black line, called the lubber-line, in the absolute direction of a vertical plane cutting the ship from stem to stern. The helmsman must keep the division of the card which shows his course in contact with the lubber-line.

The compass first used in the Mediterranean was simplicity itself, being merely a piece of lodestone attached to a cork floating in a vessel of water.

It has been found by astronomical observation that the needle does not strictly point due north and due south, but varies sometimes to the east, sometimes to the west, of true geographical north and south. The stars are fixed, and never vary in their relative positions. The variation or declination of the needle for any place or time is found by comparing a star's bearing, as indicated by the needle, and its bearing, as shown by astronomical calculation. Columbus was among the first to notice the variation of the needle. He certainly was the first to perceive that there was a line of no variation. There are places upon the earth's surface where the direction of the needle coincides exactly with the geographic meridian, and these places, connected together by an imaginary and very irregular curve, form the so-called lines of no variation. It is generally admitted that there are two lines of this character, called the east and west line. The course of the west line may be traced from the sixtieth parallel of latitude to the west of Hudson's Bay, thence in

THE MARIISTER'S COMPASS. 21

a southern direction through the American lakes, to the West Indies, and the extreme eastern point of South America.

The eastern, beginning in the White Sea, runs south in a semicircle until it reaches the seventyfirst parallel ; it thence runs along the Sea of Japan, whence it takes a westward course across China and Hindostan to Bombay; it then turns east, touches Australia, and goes south. Even these lines are not constant, but move from time to time.

A great deal of care and time have been expended by navigators on this matter of the needle's variation. Their observations have, in a great measure, been systematized, so that they have made elaborate charts and tables of the vagaries of this priceless but too sensitive guide. In the year 1840 General Sabine employed as many as fourteen hundred and eighty observations, to accurately determine the line of no variation in the Atlantic Ocean. It may be remarked, however, that for the ordinary purposes of navigation the needle points toward the north with sufficient accuracy, and the variations may in general be disregarded. When, indeed, there is question of something requiring great delicacy and precision, the proper corrections must be applied.

The magnetic needle has a small daily and even hourly variation. Its north pole declines slightly to the west from sunrise to an hour past noon, then retrogrades toward the east until eight in the evening, and remains stationary during the night. It has, moreover, an annual movement, and a different movement in winter from that in summer. These daily and yearly fluctuations of the needle depend, in all probability, upon the differences of temperature caused by the apparent course of the sun.

The magnetic needle is also more or less disturbed by meteoric showers, electric storms, the aurora borealis, the lightning's flash, and the volcano's throe.

If the magnetic needle be so supported at its center of gravity that, instead of being free to move in a horizontal plane, it is left free to move in a vertical plane, the needle will be found to incline more or less from a horizontal position according to the location on the earth's surface. When north of the equator, the north pole of the needle will incline downward; and, when south, the south pole will incline or dip. A magnetized needle of this kind is called a dipping needle. It is furnished with a graduated scale,

THE MARINER'S COMPASS. 23

circular in form, marking all the degrees of an arc, and situated in a vertical plane just beside the needle. In the construction of the dipping-needle, as in that of the compass - needle, everything is done to reach the minimum of friction. Two tiny steel cylinders are run out from the needle on each side of its center of gravity, and these rest on knife-edges made of agate. The frame supporting the needle is mounted on a tripod having adjusting screws, in order to maintain a perfect level.

The nearer this needle is brought to the magnetic equator, the nearer its approach to a horizontal position, and consequently the less the dip or inclination. The farther it is moved from the magnetic equator in the direction of the magnetic pole, the greater the dip. The magnetic equator is where the needle assumes a perfectly horizontal position, being equally influenced by both poles. The magnetic equator does not correspond exactly with the geographic equator, but makes with it an angle of twelve or thirteen degrees.

The geographic equator of the earth is a perfect curve, or great circle ; but the magnetic equator is an irregular double curve, to which the name of aclinic line has been given. The magnetic equa-

24: ELECTKICITY AND ITS DISCOVERERS.

tor intersects the geographic equator in several places : one point of intersection is in the Island of St. Thomas, and another in the Pacific Ocean, about 142° longitude east from Greenwich. This aclinic line is, however, constantly changing its position.

The magnetic poles of the earth do not coincide with the geographic poles. When the dipping-needle is held directly over the magnetic north pole of the globe, the needle will take a perfectly vertical position, the north pole of the needle pointing downward. If we could place the needle over the south magnetic pole, the needle would assume a perpendicular attitude, the south pole pointing downward.

Sir James Ross, in 1831, trying to find a northwest passage around the American Continent, when in latitude 70° 5' 17", near Hudson's Bay, saw the needle take a vertical position. The south magnetic pole has not been located.

When the needle of the compass is placed in the immediate neighborhood of one of the magnetic poles of the earth, it loses its power altogether, and points indifferently in all directions. If a magnetized needle be placed on a cork floating in a pool of water, after a short time the

THE MARINER'S COMPASS. 25

poles of the needle will so arrange themselves as to point permanently north and south, but the cork will not be drawn toward either the north or south 6hore. From this it is concluded that the influence the earth exercises upon the needle is not attractive, but merely directive.

The intensity of the earth's action upon the magnetic needle varies in different places. The nearer the needle is approached to the magnetic poles, the more sensitive it grows, and the more striking and vivid its movements. As we draw near to the equator, the effect is seen to become more and more feeble.

The intensity of the earth's magnetism is found to be greater in colder than in warmer climes. This intensity is also noticed to be greater in the western and northern than in the eastern and southern hemispheres. The earth's magnetism displays itself with a greater intensity at the following places, in the order in which they are named : St. Petersburg, London, Berlin, Paris, Vienna, Madrid, Rome.

Chapter III. Michael Faraday

Michael Faraday, most probably the greatest experimental physicist that ever lived, was the son of very poor parents, his father being a journeyman blacksmith. Michael was born at Newington Butts, near London, on the 22d of September, 1791 ; and, ten years later, necessity forced his family to seek public relief during a period of great distress in London.

In his thirteenth year he went as newspaper-boy to Mr. George Riebau, a bookseller on Blandford Street; and in his own simple way he tells the hardships of this task : " It was his duty, when he first went, to carry round the papers that were lent out by his master. Often on a Sunday morning he got up very early and took them round, and then he had to call for them again ; and frequently, when he was told the paper was not done with, 6 You must call again, 5 he would beg to be allowed to have it, for his next place might be a mile off, and then he would have to return back over the ground again, losing much time, and being very unhappy if he was unable to get home to make himself neat, and to go with his parents to their place of worship." A year later he became an apprentice to Mr. Riebau, and continued in his establishment for eight years. Having an extraordinary taste for reading scientific works, he spent every leisure moment in this pursuit. He was especially fascinated with an article on " Electricity " that he found in an old encyclopaedia he was employed to bind, and even constructed an electrical machine consisting principally of an old bottle, and tried to verify for himself by experiment the facts referred to in the article.

While a journeyman book-binder, he had the good fortune to attend some public lectures by Sir Humphry Davy, then in the zenith of his fame. Burning with an ardent love of knowledge, and encouraged by a friend, he had the resolution to apply to Davy for employment. Sir Humphry at first tried to dissuade him from his object of following science as a profession, warning him that Science was a harsh mistress, and, in a pecuniary point of view, but poorly rewarding those who devoted themselves to her service. But nothing could withstand his thorough earnestness, and Davy engaged him as chemical assistant to the Royal Institution of Great Britain. This was the turning-point in his career, and thenceforth his life, with a lover's fervor, was dedicated to the service of science. For fifty-two years, with unexampled patience and a hero's courage, he watched and worked in Nature's inner sanctuary; and for forty of these years he kept the name of England in the first rank of science.

In the latter part of 1813 he accompanied Davy as his amanuensis to the Continent. This journey occupied a year and a half, and brought him into contact with the most noted men of science of that time. Faraday was always remarkable for his method, and so made notes of the famous places he visited, and of the great scientific experiments he witnessed. These notes show the goodness and manliness of his heart, and the early perspicacity of his judgment. On his return to the Royal Institution the rapid progress he made in self-education was marvelous. His work for the next five years in the laboratory and lecture-room was 60 brilliant as to place him by the side of the first chemists of the day. During this period, also, his life had been one of uninterrupted happiness. But human life is a current that must inevitably flow through rough and broken passages. In his thirtieth year he was unjustly accused of dishonesty, in claiming for himself a discovery of the great Dr. Wollaston in magnetism. This persecution, as undeserved as it was venomous, instead of injuring him, rather served to bring into a brighter light his truth and integrity. Another source of great annoyance to him at the same time was the opposition given by Sir Humphry Davy, through a motive of petty jealousy, to his election as Fellow of the Royal Society. His conspicuous ability, however, triumphed over all obstacles, and on January 8, 1824, he was all but unanimously elected. Faraday tells us that he sought and paid for this title, but it was the only one he ever afterward solicited.

The first mark of honor paid to Faraday's scientific labors was in his thirty-second year, and came from the Cambridge Philosophical Society. The same year he was elected corresponding member of the French Academy of Sciences, and of the Accademia dei Georgofili of Florence. During his lifetime Faraday received ninety-five honorary titles and marks of merit from learned bodies throughout the world, all coming voluntarily and unsolicited. In his thirty-fourth year he was appointed Director of the Laboratory of the Royal Society.

Faraday always had one of the kindliest natures. When in the height of his fame, one of his nieces says of him : " In times of grief or distress his sympathy was always quick, and no scientific occupation ever prevented him from sharing personally in all our sorrows, and comforting us in every way in his power. Time, thoughts, purse, everything was freely given to those who had need of them."

On October 17, 1831, being in his fortieth year, Faraday made the great discovery of his life, and one that will make his name famous t ' for all time to come. He discovered magneto-electricity. It was the reward of seven years of unceasing labor and unwavering scientific faith. In 1824 he had reasoned himself into the belief that this discovery was possible. Professor Oersted, of Copenhagen, about twelve years previously, discovered by accident electro-magnetism, or, that a current of electricity, passing through a wire coiled around a piece of soft iron, will magnetize the iron. Faraday, not by accident, but as the consequence of a clear idea, discovered magneto-electricity, or that a magnet will induce an electric current in a coil of wire. The instant the magnet is inserted in the coil, it induces a current in one direction, and when it is withdrawn it induces a current in the opposite direction. These currents are but momentary ; when the magnet rests in the coil, no electricity is perceptible.