V.DYNAMO AND MOTOR.

A GRAPHOPHONE.

In that year (1877), Edison, in striving to make a self-recording telephone by connecting with its diaphragm or disk a stylus or metal point which would record its vibrations upon a strip of tinfoil, accidentally reversed the motion of the tinfoil so that the tracings upon it affected the stylus or tracing-point in an opposite direction. To his surprise, he found that this reverse motion of the tinfoil, tickling, as it were, the stylus oppositely, reproduced the sounds which had at first agitated the diaphragm. It was but a step now to the production of his matured phonograph in 1878. He made a cylinder with a grooved surface, over which he spread tinfoil. A stylus or fine metal point was made to rest upon the tinfoil, so as to produce a tracing in it, following the grooves in the cylinder when the latter was made to revolve. This stylus was connected with the diaphragm of an ordinary telephone transmitter. When one spoke into the transmitter, that is, set the diaphragm to vibrating, the stylus impressed the vibratory motions of the diaphragm, or, in other words, the waves of the exciting sound, in light indentations upon the tinfoil. In order to reproduce the sounds thus registered in the tinfoil of the cylinder, it was made to revolve in an opposite direction under the point of the stylus, and as the stylus was now affected by precisely the same indentations it had first made in the tinfoil, it carried the identical vibrations it had recorded back to the diaphragm of the telephone, and thus reproduced in audible form the speech that had at first set the diaphragm to vibrating. The speech thus reproduced was that of the original speaker in pitch and quality. Ingenious and wonderful as Edison’s machine was, it was susceptible of improvement, and soon Bell and others came forward with a phonograph in which the recording cylinder was covered with a hardened wax. This was called the graphophone. Again, Berliner improved upon the phonograph by using for his tracing surface a horizontal disk of zinc covered with wax. By chemical treatment, the tracings made in the wax were etched into the zinc, and thus made permanent. Edison made further and ingenious improvements upon his phonograph by attaching hearing tubes for the ear to the sound receiver, and by the employment of an electric motor to revolve the wax cylinder. By the attachment of enlarged trumpets and other devices, every form of modern phonograph has been rendered capable of reproducing in great perfection the various sounds of speech, song, and instrument, and has become a most interesting source of entertainment.

Dynamo is from the Greekdunamis, meaning power. Motor is from the Latinmotus, ormoveo, to move. Dynamo is the every-day term applied to the dynamo-electric machine. Motor is the every-day term applied to the electric motor. The dynamo and motor are quite alike in principle of construction, yet direct opposites in object and effect. Perhaps it might be well to designate both as dynamo-electric machines, and to say that, when such machine is used for the conversion of mechanical energy or power of any kind into electrical energy or power, it is a dynamo. When a reverse result is sought, that is, when electrical energy or power is to be converted into mechanical energy or power, the machine that is used is a motor. In practical use for most purposes they are brought into coöperation, the dynamo being at one end of an electric system, making and sending forth electricity, the motor being at the other end, taking up such electricity and running machinery with it. Both machines were epoch-making in the midst of a wondrous century, and both were results of those marvelous evolutions in electrical science which characterized the earlier years of the century.

We have seen how the simple glass cylinder or sulphur roll became, when rubbed, a generator of electricity. In a later chapter of electrical history, we saw a new and more powerful generator of electricity in the voltaic cell, by means of opposing metals acted upon chemically by acids. The greatest, grandest, most powerful, and most economic of all generators of electricity was yet to come in the shape of the dynamo. We see its beginnings in those investigations of Faraday which led to the discovery of the induction coil and the principles of magneto-electric induction. In 1831, he invented a simple yet, for that date, wonderful machine, which was none the less the first dynamo in principle, because he modestly called it “A New Electrical Machine.” He mounted a thin disk of copper, about twelve inches in diameter, upon a central axis, so that it would revolve between the opposite poles of a permanent magnet. As the disk revolved, its lower half cut the field of force of the magnet, and a current was induced which was carried away by means of two collecting brushes, fastened respectively to the axis and circumference of the disk. This was the first electric current ever produced by a permanent magnet. The Faraday machine and others that derived the mechanical energy which was converted into electric current from a permanent magnet were classed as magneto-generators. Soon the electro-magnet took the place of the permanent magnet, because it produced a much stronger field of force. But then the electro-magnet had to have a current to excite it. This current was supplied by a magneto-generator, placed somewhere on the dynamo. Now came the thought, suggested by Brett in 1848, that the induced currents of the dynamo could themselves be turned to account for increasing the strength of the electro-magnets used in inducing them. This was a most progressive step in the history of the dynamo. It led to rapid inventions, whose principle was based on the fact that every dynamo carried within the cores of its magnets enough of unused or residual magnetism to render the magnets self-exciting the moment the machine started. So the outside means of magnetizing the fields of force of the dynamo passed away.

The dynamo speedily grew in size and importance. The electro-magnetsor fields of force were greatly increased in number, size, and power. There were great improvements in the construction and efficiency of the wire coils or armatures which cut the fields of force, and a corresponding increase in their number. Commutators and brushes underwent like improvement. So, at last, the well-nigh perfect and all-powerful dynamo of the end of the century was evolved, with a capacity for delivering, in the form of electricity, ninety per cent of the mechanical energy which set it in motion. In the application of steam to machinery, eighty per cent, and sometimes more, of the energy supplied by a ton of coal is lost.

A DYNAMO.

With the perfection of the dynamo, its uses multiplied. It became a prime factor in electric lighting. Trolley systems sprang up in city, town, and village, taking the place of horse and traction cars. In certain places, as in the Baltimore tunnel, the dynamo superseded the engine for hauling freight and passenger cars. The mighty dynamos which convert the inexhaustible energy of Niagara Falls into electricity send it many miles away to Buffalo, to be applied to lighting and to every form of machinery. The end of the century sees a power plant in operation in New York city capable of furnishing one hundred thousand horse-power, or enough to supply the lighting, rapid transit, and thousand and one mechanical needs of the entire municipality. The essential parts of an ordinary dynamo are: (1.) The electro-magnets, which,however numerous, are arranged in circular form upon part of the framework of the machine. (2.) The iron coils or armatures, mounted in a circle upon a wheel. When the wheel revolves, the armatures pass close in front of the electro-magnets, cutting through their fields of force, and thereby inducing electric current. (3.) The commutator, which consists usually of a series of copper blocks arranged around the axle of the armatures, and insulated from the axle and from each other. The current passes from the armatures to the commutator. If the current be an alternating one, the commutator changes it into a continuous one, and the reverse may also be accomplished. (4.) The brushes, which are thin strips of copper or carbon, are brought to bear at proper points upon the commutator, making connection with each coil or sets of coils. They carry the corrected current to the outside line or lines. (5.) The outside line or lines, to carry the current away to the motor. (6.) The pulley for strap-belting, by means of which the water or steam power used is made to turn the dynamo machine.

But we must not forget the motor as a companion of the dynamo, as its indispensable brother, in turning to practical account the electricity sent to it. As we have seen, the motor is the reverse of the dynamo, at least in its effects. It is fed by the dynamo, and it imparts its power to the machinery which it is to set in motion. It is to the dynamo what the water-wheel is to the water. In one sense it is an even older invention than the dynamo, but its extended commercial application was not possible until the dynamo had reached certain stages of perfection. It is generally agreed that the first motor of importance was that constructed by Professor Jacobi, through the liberality of the Czar Nicholas, of Russia. Jacobi used two sets of electro-magnets, by means of whose mutual attraction and repulsion he rotated a wheel on a boat with a power equal to that of eight oarsmen. But as Jacobi’s electro-magnets required an electric current to magnetize them, and as there were then no means of producing such current except by the costly use of the voltaic battery, his invention was unripe as to time.

In 1850, Professor Page, of the Smithsonian Institution, constructed a motor which worked ingeniously, but was still open to the objection of cost in supplying the necessary electric current for the electro-magnets. Though various inventions came about having for their object a commercially successful motor, such a thing was impossible till Gramme produced his improved and effective dynamo in 1871. This dynamo was found to work equally well as a motor, and hence it became necessary for electricians to greatly enlarge their understanding of the nature of electro-magnetic induction. They soon discovered many curious things respecting the behavior of induced currents, with the result that rapid and simultaneous improvements were made in both dynamos and motors. One of the most curious of these discoveries was that a motor automatically regulates the amount of current that passes through its circuit in proportion to the work it is called upon to do; that is, if the work the machine has to do is decreased, the motor attains a higher speed, which higher speed induces a counter electro-motive force sufficient to check up the amount of current passing through the motor. So when the motor is required to do increased work, the machine slows up; but with this slowing up, the counter electro-motive force decreases, and consequently the current passing through the motor increases.

As with the dynamo, one of the marvels of the motor is its efficiency. In perfect machines, ninety to ninety-five per cent of the electrical energy supplied can be converted into mechanical energy. For this reason it has become a competitor with, and even successor of, steam in countless cases, and especially where water-power can be commanded. A prime motor, in the shape of a water-wheel, may be made to drive scores of secondary motors in places hundreds of miles away. The power developed by the waterfall at Lauffen, Germany, is transmitted one hundred miles to Frankfort, with a loss of only twenty-five per cent of the original horse-power.

THE GOLDEN CANDLESTICK.

In its adaptation for practical use, the motor, like the dynamo, assumes all sizes and embraces a host of ingenious devices, yet its power and usefulness always centre around, or are contained in, its two efficient parts, its armatures and fields of force. We have seen how in the dynamo the armatures became the source of induced currents by being made to cut the fields of force of electro-magnets. Now, a dynamo can be made to work in an opposite way; that is, by making the magnetic fields of force rotate in front of the coils or armatures. In the motor, the field of force is mostly established by the current directly from the dynamo. This current passes also through the armature, which begins to rotate, owing to the force of the field upon it. This rotation of the armature through the field of force produces in the armature conductors an electro-motive force, which is the measure of the power of the motor, be the same great or small.

ANCIENT LAMP.

Mention of the “candlestick of pure gold” (Ex. xxv. 31) may lead to the inference that the primitive artificial light was that of the candle. But “candlestick” in connection with the lighting of the temple is clearly a misnomer. The lamp was the original artificial light-giver, unless we choose to except the torch; and if less indispensable than in patriarchal times, it is still a favorite dispenser of nightly cheer. Prior to the middle of the eighteenth century, the lamp had practically no evolution. It was the same in principle at that date as when it illuminated the desert tabernacle. Even the splendid enameled glass or decorated Persian pottery lamps of Damascus and Cairo, and the magnificent brass or bronze lamps of Greece, Rome, and the European cathedrals, gave forth their dull, unsteady flame and noisome smoke by means of a crude wick lying in a saucer or similar receptacle of melted lard, tallow, oil, or some such combustibleliquid. A prime improvement was made in lamp-lighting in 1783, by Leger, of Paris, who devised the flat, metallic burner, through which he passed a neatly prepared wick. A further improvement was made in 1784 by Argand, of Paris, who introduced a burner consisting of two circular tubes, between which passed a circular wick. The inner tube was perforated so as to admit of a draught of air to feed the flame on the inside of the wick. In order to similarly feed the flame on the outside of the wick, he invented the lamp chimney, which was at first a crude thing of metal. It, however, soon gave way to the glass chimney, which has up to the present taken on many improved forms, designed to secure more perfect combustion and a brighter, steadier glow.

TALLOW DIP.

MODERN LAMP.

Improvement in lamp-lighting during the nineteenth century has consisted of an indefinite number of inventions, all aiming at economy, brilliancy, steadiness, convenience, beauty, and so on. But in no respect has this improvement been more rapid and radical than in the adaptation of lamps to the various combustible fluids that have bid for favor. While the various oils, animal and vegetable, were almost solely in vogue as illuminants at the beginning of the century, they were largely superseded at a later period by the burning-fluid known as camphene. This was a purified oil of turpentine, which found great favor on account of its economy, convenience, cleanliness, and brilliancy of light. But it was very volatile, and its vapors formed with air a dangerously explosive mixture. Yet with all this it might have held its own for a long time, had not Gesner, in 1846, discovered that a superior mineral oil, which he called “kerosene,” could be readily and profitably distilled from the coal found on Prince Edward Island. This kerosene or hydrocarbon oil speedily displaced camphene as an illuminant. Its manufacture rapidly developed into an important industry in the United States, and large distilling establishments arose, both on the Atlantic coast, where foreign coal was used, and throughout the country, wherever cannel or other convertible coal was found. With the discovery of petroleum in paying quantities on Oil Creek, Pa., in 1859, there came about a great change in kerosene lamp-lighting. It was found, upon analysis, that crude petroleum contained about fifty-five per cent of kerosene, which constituted its most important product. The manufactories of kerosene from cannel or other coal, therefore, went out of existence, and new ones, larger in size and greater in number, sprung up for the manufacture of kerosene or, popularly speaking, coal oil, from petroleum.This illuminant came into almost universal favor for lamp use, owing to its cheapness and brilliancy. It is not free from danger when improperly distilled, but under the operation of stringent laws governing its preparation and testing, danger from its use has been reduced to a minimum. In rural districts, in smaller towns and villages, wherever economy and convenience are essentials, and when beauty in lamp effects is desirable, the kerosene illuminant has become indispensable.

The discovery of petroleum helped further to light the world and distinguish the century. It gave us gasolene, naphtha, gas oil, astral oil, and the very effective “mineral sperm,” which is almost universally used in lighthouses and as headlights for locomotives. With the addition of kerosene, a favorite light of the beginning of the century—the tallow dip of our grandmothers—began to fall into disuse. The homelike pictures of housewives at their annual candle-dippings, or in the manipulation of their moulds, became venerable antiques. Candle-light paled in the presence of the higher illuminants. Though still a convenient light under certain circumstances, it plays a gradually diminishing part amid its superiors.

One of the signal triumphs of the century has been the introduction of gas-lighting. Though illuminating gas made from coal was known as early as 1691, it did not come into use, except for experiments or in a very special way, until the beginning of the nineteenth century. In 1809, a few street lamps were lit with gas in London. An unsuccessful attempt was made to introduce gas into Baltimore in 1821. Between 1822 and 1827, the gas-light began to have a feeble foothold in Boston and New York. Other cities began to introduce it as an illuminant in streets and, eventually, in houses. But the process was very slow, owing to intense opposition on the part of both savants and common people, who saw in it a sure means of destruction by poison, explosion, or fire. It was not much before the middle of the century that prejudice against illuminating gas was sufficiently allayed to admit of its general use. But meanwhile many valuable experiments as to its production and adaptation were going on. The most productive source of illuminating gas was found to be bituminous coal. Though gas could be produced by distillation from other substances, such as shale, lignite, petroleum, water, turf, resins, oils, and fats, none could compete in quality, quantity, and economy with what is known as ordinary coal gas, at least, not until the time came, quite late in the century, when it was found that non-luminous gases, such as water gas, could be rendered luminous by impregnating them with hydrocarbon vapor. This became known commercially as water gas, and it is now largely used in place of coal gas, because it is cheaper and, for the most part, equally effective as a luminant.

Gas-lighting has, of course, its limitations. It is not adapted for use beyond the range of cities or towns whose populations are sufficient to warrant the large expenditures necessary for gas plants. It is a special rather than general light. Yet within its limited domain of use it has proved of wonderful utility,—a source of cheer for millions, a clean, safe, and economic light, a convenience far beyond the candle, the lamp, or any previous lighting appliance. In the street, it is a source of safety against thieves and way-layers. In the slums, it is both policeman and missionary, baffling the wrong-doer, exposing the secrecy that conduces to crime, laying bare the hotbeds ofshame. It is as well a source of heat as light, and consequently convertible into power for light mechanical purposes. In the kitchen, it is more and more becoming a boon to the housewife, who by means of the gas range escapes, in cooking, much of the dust, smoke, worry, and even expense of the coal cook stove and range. In the parlor, library, or sick-room, it is a cheerful and effective substitute for the coal grate, and may be made to assume the cosy qualities and fantastic shapes of the old-fashioned wood fire. Coincident with the discovery of petroleum, its inseparable companion, natural gas, came into prominence as a source of both light and heat, or this became true, at least, after it was ascertained that natural gas regions existed which could be tapped by wells, and made to give forth their gaseous product independent of the oil that may have at one time existed near or in connection with it. This natural source of light and heat became as interesting to the geologist, explorer, and capitalist as the source of petroleum itself, and soon every likely section was prospected, with the hope of finding and tapping those mysterious caverns of earth in which the pent-up luminant abounded in paying quantities. It was found that workable natural gas regions were numerous in the United States, especially in proximity to petroleum or bituminous coal deposits, and little time was lost in their development. As if by magic, a new and profitable industry sprang into existence. The natural gas well became almost as common as the oil well, and at times far more awe-inspiring as it shot into space its volcanic blasts which, when ignited through carelessness, as sometimes happened, carried to the vicinage all the dangers and terrors of Vesuvius or Stromboli. Powerful as was the force with which natural gas sought its freedom, wonderful as was the phenomenon of its escape from the subterranean alembic in which it was distilled, human genius quickly harnessed it by appliances for conservation and carriage to places where it could be utilized. Sometimes great industries sprang up contiguous to the wells; at others, it was carried through pipes to cities many miles distant, where it became a light for street, home, and store, and a prodigious energy in factory, furnace, forge, and rolling-mill. In fact, no marvel of the century has been at once so weird and inscrutable in its origin as natural gas, or more potential as an agency within the areas to which its use is limited. The question is ever uppermost in connection with natural gas, will it last? The gas springs of the Caucasus Mountains have been burning for centuries. But that is where nature’s internal forces have their correlations and compensations. Where it is quite otherwise, that is, where the vents of natural gas reservoirs are abnormally numerous, or where those reservoirs are drained to the extreme for commercial purposes, not to say through sheer wastefulness, the geologist is ready to surmise that the natural gas supply cannot be a perpetual one.

But one of the most magnificent triumphs of the century in the matter of light came about through the agency of electricity. We have already seen the beginnings of electric lighting in the discovery of Sir Humphrey Davy, in 1809, that when the ends of two conducting wires, mounted with charcoal pieces, were brought close together, a brilliant light, in the shape of an arc or curve, leaped from one piece of charcoal to the other. Davy’s charcoal pieces or carbons were consumed by the fierce heat evolved; but the principle was established that an electric current, so interrupted, was a vivid light-producer, and might be made permanently so if a substance capable of resisting the heat could be substituted for his charcoal tips, and a generator of electricity of sufficient power and economy in use could be substituted for his voltaic batteries or cells.

Upon these two essentials hung the future of the electric light. The first essential, that of a substance at the ends of the wires or in the midst of the electric circuit which would resist the heat, was soon met by the use of specially prepared and hard graphite carbon tips, in the shape of candles. But the second essential, a generator of electricity cheaper and more powerful than the voltaic cell, was not met with till the dynamo machine reached an advanced stage of perfection; that is, about 1867.

ELECTRIC ARC LIGHT.

The two grand essentials now being at command, invention of electric light appliances went on rapidly upon two lines, eventuating in two systems, which became known as arc lighting and incandescent lighting. By 1879–80, the arc light was sufficiently advanced to meet with favor as an illuminant for streets, railway stations, markets, and any large spaces, in which places it became a substitute for gas and other lights. The essential features of the arc light are: (1.) The dynamo machine, situated in some central place, for the generation of electricity. (2.) Conducting wires to carry the electricity throughout the areas or to the places to be lighted. (3.) The arc lamp, which may be suspended upon poles in the streets, or upon wires in stores and other covered places. Its mechanism consists of two pencils or candles of graphite carbon, very hard and incombustible, adjusted above and below each other so that their tips or ends are very close together, but not in contact. By means of a clockwork or simple gravity device these carbon tips are brought into contact at the moment the electric current is turned on, and then are slightly separated as soon as the current has heated them. The air between the heated tips, having also reached a high temperature, becomes a conductor, and the electricity leaps in the form of an arc or curve through it, rendering it brilliantly incandescent. Should the current be diminished in strength for any reason, the above-mentioned clockwork or gravity device brings the carbons a little closer together; and should the current be increased, the carbons are separated a little wider; thus the steadiness of the light is regulated. There are also various automatic devices for thus regulating the proximity of the carbons and maintaining the evenness of the glow. The power of an arc light is measured by candles. An ordinary arc light under two amperes of current gives a light equal to twenty-five candles, while under fifty amperes of current it gives a light equal to twenty thousand candles. In searchlights on board vessels, and where very large areas are to be lighted, both heavier currents and larger carbons are used than in the arclamps for ordinary street purposes. No light surpasses the arc light in brilliancy, excepting the magnesium light. There are few cities in this country and Europe that do not employ the arc lamp as a means of street, station, and large-area lighting, owing to its superiority as an illuminant and the wonderful policing effect it has upon the slum sections.

The incandescent lamp, or electric lighting by incandescence, underwent a somewhat longer evolution at the hands of inventors than the arc lamp, owing to the difficulty of finding a substance suitable for the production of the necessary glow. The discovery of such substance may be accredited to Edison more fully than to any other. The incandescent or glow lamp is a glass bulb from which the air is exhausted. There passes into the bulb a filament of carbon, which, after a turn or two inside the bulb, passes out at the end through which it entered. When a current from a voltaic battery is sent through this carbon filament, it brings it, in the absence of oxygen within the bulb, to a high white heat without combustion. The portion of this high white heat which is radiated is the light-giving energy of the incandescent lamp. Metal filaments were at first tried in the bulb, but they quickly burned out. Carbon filaments were at length found to be the only ones capable of resisting the heat. They moreover had the advantage of cheapness, and of greater radiating energy than metals. Many substances, such as silk, cotton, hair, etc., were used in the preparation of the carbon filaments, but it was found that strips cut from the inside bark of the bamboo gave, when brought to a white heat by an electric current and then properly treated, the most tenacious and best conducting carbon filament.

The quality of light produced by an incandescent lamp is a gentler glow than that produced by the arc lamp, and in color more nearly resembles the light of gas or the oil lamp. The incandescent light speedily became for the home, hotel, hall, and limited covered area what the arc light became for the street and railway station, and, if anything, the former outstripped the latter in the extent and value of the industry it gave rise to.

In the arc lamp, the carbon pencils have to be renewed daily. In the incandescent lamp, the carbon filament, though very delicate, may last for quite a time, because incandescence takes place in the absence of oxygen. If the favor in which the electric light is held, and the great extent of its use, rested solely on the question of cheapness of production, such question would give rise to interesting debate. And, indeed, the debate would continue, if the question were the superior fitness of electric lighting for lighthouses and like service, where extreme brilliancy does not seem to penetrate a thick atmosphere as effectively as the more subdued glow of the oil lamp. But the debate ceases when the question is as to the beauty and efficiency of the electric light in the home, street, station, mine, on shipboard, and the thousand and one other places in which it has come to be deemed an essential equipment. In all such places the question of economy of production and use is subordinate to the higher question of utility and indispensability.

The dawn of the nineteenth century saw, as vehicles of locomotion, the saddled hackney, the clumsy wagon, the ostentatious stage-coach, the primitive dearborn, the lumbering carriage, the poetic “one-hoss shay.” Theuniversal energy was the horse. A new energy came with the application of steam, and with it new vehicular locomotion,—easier, swifter, stronger, for the most part cheaper, rendering possible what was hitherto impossible as to time and distance.

This signal triumph of the century may not have been eclipsed by the introduction of subsequent locomotive changes, but it was to be supplemented by what, at the beginning, would have passed for the idle dream of a visionary. The horse-car came, had its brief day, and went out with all its inconveniences, cruelties, and horrors before, in part, the traction-car, and, in part, the rapidly revolutionizing energy of electricity.

ELECTRIC LOCOMOTIVE.

The first conception of a railway to be operated by electricity dates from about 1835, when Thomas Davenport, of Brandon, Vt., contrived and moved a small car by means of a current from voltaic cells placed within it. In 1851, Professor Page, of the Smithsonian Institution, ran a car propelled by electricity upon the steam railway between Washington and Baltimore, but though he obtained a high rate of speed, the cost of supplying the current by means of batteries—the only means then known—prohibited the commercial use of his method.

With the invention of the dynamo as an economic and powerful generator of electricity, and also the invention of the motor as a means of turning electrical energy to mechanical account, the way was open, both in the United States and Europe, for more active investigation of the question of electric-car propulsion. Between 1872 and 1887, different inventors, at homeand abroad, placed in operation several experimental electric railways. Few of them proved practical, though each furnished a fund of valuable experience. An underground electric street railway was operated in Denver as early as 1885; but the one upon the trolley plan, which proved sufficiently successful to warrant its being called the first operated in the United States, was built in Richmond, Va., in 1888. It gave such impetus to electric railway construction that, in five years’ time, enormous capital was embarked, and the new means of propulsion was generally accepted as convenient, safe, and profitable.

The essential features of the electric railway are: (1.) The track of two rails, similar to the steam railway, (2.) The cars, lightly yet strongly built. (3.) The power-house, containing the dynamos which generate the electricity. (4.) The feed-wire, usually of stout copper, running the length of the tracks of the system, and supported on poles or laid in conduits. (5.) The trolley-wire over the centre of the track, supported by insulated cross-wires passing from poles on opposite sides of the tracks, and connected at proper intervals with the feed-wire. (6.) The trolley-pole of metal jointed to the top of the car, and fitted with a spring which presses the wheel on the end of the pole up against the trolley-wire with a force of about fifteen pounds, and which also serves to conduct the electricity down through the car to the motor. (7.) The motor, which is suspended from the car truck, and passes its power to the car axle by means of a spur gearing. The power requisite for an ordinary trolley-car is about fifteen horse-power. The speed of trolley-cars is regulated in cities to from five to seven miles per hour, but they may be run, under favorable conditions, at a speed equal to, or in excess of, that of the steam-car.

As a means of city transit, and of rapid, convenient, and economic intercourse between suburban localities and rural towns and villages, the electric traction system ranks as one of the greatest wonders of the century. The speed with which it found favor, the enormous capital it provoked to activity, the stimulus it gave to further study and invention, the surprising number of passengers carried, go to make one of the most interesting chapters in electric annals. The end of the century sees thousands of these electric roads in existence; a comparatively new industry involving over $100,000,000; a passenger traffic running into the billions of people; a prospect that the trolley will succeed the steam-car for all utilizable purposes within the gradually extending influence of cities and towns upon their rural surroundings.

In speaking of the passing of the horse-car and its substitution by the trolley, a distinguished writer has well said: “Humanity in an electric-car differs widely from that in the horse-car, propelled at the expense of animal life. It is more cheerful, more confident, more awake to the energy at command, more imbued with the subtlety and majesty of the propelling force. The motor confirms the ethical fact that each introduction of a higher material force into the daily uses of humanity lifts it to a broader, brighter plane, gives its capabilities freer and more wholesome play, and opens fresh vistas for all possibilities. We applaud Franklin for seizing the lightning in the heavens, dragging it down to earth, and subjugating it to man. Let this pass as part of the poetry of physics. But when ethics comes to poetize, let it be said that electricity as an applied force lifts man up toward heaven,quickens all his appreciations of divine energy, draws him irresistibly toward the centre and source of nature’s forces. There is no dragging down and subjugation of a physical force. There is only a going out, or up, of genius to meet and to grasp it. Its universal application means the raising of mankind to its plane. If electricity be the principle of life, as some suppose, what wonder that we all feel better in an electric-car than any other? The motor becomes a sublime motive. God himself is tugging at the wheels, and we are riding with the Infinite.”

ELECTRIC RAILWAY. THIRD RAIL SYSTEM.

Enthusiasts say the trolley is only the beginning of electric locomotion, and that there is already in rapid evolution an electric system which will supersede steam even for trunk-line purposes. In vision, it presumes a speed of one hundred and twenty-five miles an hour instead of forty; greater safety, cleanliness, and comfort; and what is most momentous and startling, an economy in construction and operation which will warrant the sacrifice of the billions of dollars now invested in steam-railway properties. The proposition is not to sacrifice the steam-railway track, but to add to it a third rail, which is to carry the electric current. Then, by means of feed-conduits alongside of the track, and specially constructed electric locomotives and cars, the system is supposed to reach the practical perfection claimed for it. Experiments with such an electrical system, made upon branch lines of some of our trunk-line railways,as the Pennsylvania, New York Central, and New Haven & Hartford, give much encouragement to the hypothesis that it may become the next great step in the evolution of electrical science.

Another means of electric propulsion was provided by the investigations of Planté, which resulted in his invention of the “accumulator” or “storage battery,” in 1859. His battery consists of plates of lead immersed in dilute sulphuric acid. By the passage of an electric current through the acid, it is electrolytically decomposed. By continuing the current for a time, first in one direction and then in another, the lead plates become changed, the one at the point where the current leaves the cell taking on a deposit of spongy lead, and the one at the point where the current enters the cell taking on a coating of oxide of lead. When in this condition, the battery is said to be stored, and is capable of sending out an electric current in any circuit with which it may be connected. After exhausting itself, it can be re-stored or re-charged in the same way as at first. Faure greatly improved on Planté’s storage battery in 1880, by spreading the oxide of lead over the plates, thus greatly reducing the time in forming the plates. Subsequently, further improvements were made, till batteries came into existence capable of supplying a current of many hundred amperes for several hours. One of the first practical uses to which the storage battery was put was in the propulsion of street-cars; but its weight proved a drawback. It was found better adapted for the running of boats on rivers, and, in the business of water-freightage for short distances, has in many instances become a rival of steam. It found one of its most interesting applications in helping to solve the problem of theautomobile, or “horseless carriage,” either for pleasure purposes or for street traffic. In this problem it has, at the end of the century, an active rival in compressed air; but as the “horseless carriage” is rapidly coming into demand, means may soon be found to utilize the strong and persistent energy of the storage battery, without the drawback found in its great weight.

An astounding electrical revelation came during the last years of the century through the discovery of the X, or unknown, or Roentgen ray. A hint of this discovery was given by Faraday during his investigation of the effect of electric discharges within rarefied gases. He also invented the termsanodeandcathode, both of which are in universal use in connection with instruments for producing the X rays; the anode being the positive pole or electrode of a galvanic battery, or, in general, the terminal of the conductor by which a current enters an electrolytic cell; and the cathode being the negative pole or electrode by which a current leaves said cell.

Geissler followed Faraday with an improved system of tubes for containing rarefied gases for experimentation. He partially exhausted his tubes of air, introduced into them permanent and sealed platinum electrodes, and produced those wonderful effects by the discharge obtained by connecting the electrodes with the terminals of an electric machine or induction coil, which from their novelty and beauty became known as Geissler effects, just as his tubes became known as Geissler tubes. In the attenuated atmosphere of the Geissler tube, the current does not pass directly from one platinum point or electrode to the other, but, instead, illuminates the entire atmospheric space.When other gases are introduced in rarefied form, they are similarly illuminated, but in colors corresponding to their composition. In his further experiments, Geissler noted that the gases in the tube behaved differently at the anode, or positive terminal, and the cathode, or negative terminal. A beautiful bluish light appeared at the cathode, while the anode assumed the same color as the illuminated space in the tube. It was also noted that after the electric discharge within the tube, there remained upon the inner surface of the glass a fluorescent or phosphorescent glow, which was attributed to the effect of the cathode.

GEISSLER’S TUBES.

This brought the study of thecathoderays into prominence, and through the investigations of Professor William Crookes, in 1879 and afterwards, a conclusion was reached that a “Fourth State of Matter” really existed. He perfected tubes of very high vacuum, by means of which he showed that molecules of gas projected from the cathode moved freely and with great velocity among one another, and so bombarded the inner walls of the tube as to render it fluorescent.

Subsequently, Hertz showed that the cathodic rays would penetrate thin sheets of metal placed within the tube or bulb; and soon after, Paul Lenard (1894) demonstrated that the cathodic ray could be investigated as well outside of the tube or bulb as within it. He set an aluminum plate in the glass wall of the bulb opposite the cathode. Though ordinary light could not penetrate the aluminum plate, it was readily pierced by the cathodic rays, to a distance of three inches beyond its outside surface. With these rays, thus freed from their inclosure, he produced the same fluorescent effects as had been noted within the bulb, and even secured some photographic effects. These cathodic rays produced no effect on the eye, which proved their dissimilarity to light. Lenard showed further that the cathodic rays outside of the tube could be deflected from their straight course by a magnet, that they might pass through substances opaque to light, and that in so passing they might cast a shadow of objects less opaque, which shadow could be photographed. Now Professor Roentgen came upon the scene. He had been conducting his experiments in Germany, along the same lines as Lenard, and had reached practically the same results as to the penetrative, fluorescent, and photographic effects of the cathodic rays. But he had gone still further, and, in 1896, fairly set the scientific world aflame with the announcement that all the effects produced by Lenard in the limited space of a few inches could also be produced at long distances from the tube, and with sufficient intensity to depict solid substances within or behind other substances sufficiently solid to be impermeable by light. Professor Roentgen claims that his X ray is different from the cathodic ray of Lenard and others, because it cannot be deflected by a magnet. This claim has given rise to much controversy respecting the real nature of the X ray, a controversy not likely to end soon, yet one full of inspiration to further investigation.

SCIAGRAPH OR SHADOW PICTURE.By X Ray process.

SCIAGRAPH OR SHADOW PICTURE.

By X Ray process.

The essential features of the best approved apparatus designed to produce the X ray and to secure a photograph of an invisible object, are: (1.) A batteryor light dynamo as a generator of the electric current, accompanied, of course, by the necessary induction coil, which should be so wound as to give a spark of at least two inches in length in the tube where a picture of a simple object, as a coin in a purse, is desired; a spark of four inches in length where pictures of the bones of the hands, feet, or arms are desired; and a spark of from eight to ten inches in length where inside views of the chest, thighs, or abdomen are desired. (2.) The second essential is the glass tube. The one in common use is the Crookes tube, usually pear-shaped, and resting upon a stand. Into it is inserted two aluminum electrodes or disks, the one through the smaller end of the tube being used as the cathode, and the one from below and near the large end being used as the anode. (3.) A fluoroscope with which to observe the conditions inside the tube necessary to the production of the X ray, to decide upon its proper intensity, and to establish the proper degree of fluorescence. The favorite fluoroscope for this purpose is the one invented by Edison. It is in the form of a stereopticon, in which is a dark chamber after the manner of a camera. In front are two openings, admitting of a view within of both eyes. At the opposite, and greatly enlarged, end is a screen which is rendered fluorescent by means of a new substance (tungstate of calcium) discovered by Mr. Edison after some eighteen hundred experiments. Such is the power of this fluoroscope that it may be used as an independent instrument in cases of minor surgery to locate bullets or other objects buried in the flesh, even before a photograph has been taken. (4.) The photographic plate, which is prepared with a sensitized film and mounted in a frame as in ordinary photography. Upon this film the object to be photographed is laid, say, for instance, the human hand, care being taken to have the film or plate at a proper distance from the Crookes tube. Current is now turned into the tube, the X ray is developed, the film is exposed to its effects, and the result is a negative showing the interior structure of the hand,—the bones or any foreign object therein. This negative is developed as in ordinary photography.

The discovery and application of the X ray has proved of immense value in medicine and surgery. By its means the physician is enabled to carry on far-reaching diagnoses, and to ascertain with certainty the whole internal structure of the human body. Fractures, dislocations, deformities, and diseases of the bones may be located and their character and treatment decided upon. In dentistry, the teeth may be photographed by means of the X ray, even before they come to the surface, and broken fangs and hidden fillings may be located. Foreign objects in the body, as bullets, needles, calculi inthe bladder, etc., may be localized, and the surgery necessary for their safe removal greatly simplified. The beating of the heart, movement of the ribs in respiration, and outline of the liver may be exhibited to the eye. It has been boldly suggested that in the X ray will be found an agent capable of destroying the various bacilli which infest the human system, and become germs of such destructive diseases as cholera, yellow fever, typhoid fever, diphtheria, and consumption. Even if this be speculative as yet, there is still room for marvel at the actual results of the discovery of the X ray, and its future study opens a field full of the grandest possibilities.

The novel idea of keeping time by means of electricity originated quite early in the century, and culminated in two kinds of electric clocks, one moved directly by the electric current, the other moved by weights or springs, but regulated by electricity. The former have the advantage of running a very long time without attention, but as it is impossible to keep up an unvarying electric current, they are not so accurate as the latter in keeping time. Though the latter are popularly called electric clocks, they are really only clocks regulated by electricity, and in such regulation the electric current comes to be a most important agent, as is proved at all centres of astronomical and other observations, as at Greenwich and Washington. At such centres the astronomical time-keeper is set up so as to run as infallibly as possible. This central time-keeper, say at Washington, is electrically connected with other clocks, at observatories, signal-service stations, railway stations, clock-stores, city halls, etc., throughout the country. Should any of these clocks lose or gain the minutest fraction of time as compared with that of the central time-keeper, the electric current corrects such loss or gain, and so keeps all the clocks at a time uniform with one another and with the central one. Electrical devices are also often attached to individual clocks, as those upon city hall towers and in exposed places, for the purpose of meeting and correcting inequalities of time occasioned by weather exposure, expansion and contraction by heat and cold, etc.

The fatherhood of the very useful and elegant arts of electrotyping and electroplating is in dispute. Daniell, while perfecting his battery, noticed that a current of electricity would cause a deposit of copper. In 1831, Jacobi, of St. Petersburg, called attention to the fact that the copper deposited on his plates of copper by galvanic action could be removed in a perfect sheet, which presented in relief, and most accurately, every accidental indentation on the original plates. Following this up, he employed for his battery an engraved copper plate, caused the deposit to be formed upon it, removed the deposit, and found that the engraving was impressed on it in relief, and with sufficient firmness and sharpness to enable him to print from it. Jacobi called his discovery galvanoplasty in the publication of his observations in 1839. It was but a step from this discovery to the application of the electrotyping process to the art of printing. A mould of wax, plaster, or other suitable substance is made of an engraving or of a page of type. This mould is covered with powdered graphite (black lead) so as to make it a conductor of electricity. It is then inserted in a bath containing a solution of sulphate of copper. An electric current is passed through the bath, and the copper isdeposited on the mould in sufficient quantity to give it a hard surface capable of offering greater resistance in printing than the types themselves, and also of producing a clearer impression. In electroplating, practically the same principle is employed. The bath is made to contain a solution of water, cyanide of potassium, and whatever metal—gold, silver, platinum, etc.—it is designed to precipitate on the article to be electroplated. The current is then passed through the bath, and the article—spoon, knife, fork, etc.—to be electroplated receives its coating of gold, silver, German silver, platinum, or whatever has been made the third agent in the bath.

The various modern submarine devices for the destruction of ships, known as torpedoes, submarine mines, etc., depend upon electricity for their efficiency. It is the lighting or firing agent, and is carried to the torpedo or mine by means of stout wires or cables from some safe shore-point of observation.

In railroading, electricity has become an indispensable agent for the operation of signal systems, opening and closing of switches, and limitation of safety sections. It moves the drill in the mine, sets off the blast, and supplies the light. It enables the dentist to manipulate his most delicate tools and do his cleanest and least painful work. In medicine it is a healing, soothing agent, boundless in variety of application and wondrous in results. It is a stimulus to the growth of certain plants, and has given rise to a new science called Electro-horticulture. It may be made a prolific source of heat for warming cars, and even for the welding of iron and steel. The electric fan cools our parlors and offices in summer, and the electric bell simplifies household service. In fact, it would appear that, in contrasting the electrical beginnings with the electrical endings of the nineteenth century, the space of a thousand rather than a hundred years had intervened, and that in measuring the agents which conduce to human comfort and convenience, electricity is easily the most potential.

Out of the various discoveries and applications of electricity almost a new language has sprung. This is especially so of terms expressive of the measurements of electric energy, and of the laws governing the application of electric power. For a time, various nations measured and applied by means of terms chosen by themselves. This led to a jargon very confusing to writers and investigators. It became needful to have a language more in common, as in pharmacy, so that all nations could understand one another, could compute alike, and especially impart their meaning to those whose duty it became to apply discovered laws and actual calculations to practical electric operations. This was a difficult undertaking, owing to the tenacity with which nations clung to their own nomenclatures and terminologies. But the drift, though slow, finally ended at the Electrical Congress in Paris in 1881, in the adoption of a uniform system of measurements of electric force, and an agreement upon terms for laws and their application, which all could understand.

Three fundamental units of measurement were first agreed upon,—theCentimetre(.394 in.) as a unit of length; theGramme(15.43 troy grains) as a unit of mass; theSecond(1/60 of a minute) as a unit of time. These threeunits became, when referred to together by their initial letters, the basis of the C. G. S. system of units. Now by these units of measurement something must be measured, as, for instance, the electric force; and when so measured, an absolute unit of force must be the result.

Dyne:—This is but a contraction ofdynam, force. It was adopted as the name of the “Absolute Unit of Force,” or the C. G. S. unit of force, and is that force which, if it act for a second on one gramme of matter, gives to it a velocity of one centimetre per second.

Ampere:—Electrical force produces electrical current. Current must be measured and an absolute unit of current strength agreed upon. The “Absolute Unit of Current” was settled as one of such strength as that when one centimetre length of its circuit is bent into an arc of one centimetre radius, the current in it exerts a force of one dyne on a unit magnet-pole placed at the centre. But the absolute unit of current as thus obtained was decided to be ten times too great for practical purposes. So a practical unit of current was fixed upon, which is just one tenth part of the above absolute unit of current. This practical unit of current was called the ampere, in honor of the celebrated French electrician, Ampère. It may be ascertained in other ways, as when a current is of sufficient strength to deposit in a copper electrolytic cell 1.174 grammes (18.116 grains) of copper in an hour, such current is said to be of one ampere strength; or a current of one ampere strength is such a one as would be given by an electro-motive force of one volt through a wire offering one ohm of resistance.

Volt:—This was named from Volta, the celebrated Italian electrician, and was agreed upon as the unit of electro-motive force. It is that electro-motive force which would be generated by a conductor cutting across 100,000,000 C. G. S. lines in a field of force per second; or it is that electro-motive force which would carry one ampere of current against one ohm of resistance.

Ohm:—So called from Ohm, a German electrician. It is the unit of resistance offered by a conductor to the passage of an electrical current. As an absolute unit of resistance, it is equal to 1,000,000,000 C. G. S. units of resistance. As a practical unit, and as agreed upon at the International Congress of Electricians (Chicago, 1893), it represents the resistance offered to an electric current at the temperature of melting ice by a column of mercury 14.451 grammes in mass, of a constant cross-sectional area, and 106.3 centimetres in length. This is called the international ohm. The resistance offered by 400 feet of ordinary telegraph wire is about an ohm.

These three units—ampere, volt, and ohm—are the factors in Ohm’s famous law that the current is directly proportional to the electro-motive force exerted in a circuit, and inversely proportional to the resistance of the circuit; thatis,—

Current = Electro-motive force / Resistance

or,

Electro-motive force = Current × Resistance

Resistance = Electro-motive force / Current.

Erg:—From the Greekergon, work, is the unit of work required to move a force of one dyne one centimetre. One foot-pound equals 13,560 ergs.

Calorie:—Latincalor, heat, is the unit of heat; being the amount of heat required to raise the temperature of one kilogram of water one degree centigrade.

Coulomb:—In honor of C. A. de Coulomb, of France. It is the practical unit of quantity in measuring electricity, and is the amount conveyed by one ampere in one second.

Farad:—FromFaraday, the physicist. It is the unit of electric capacity, and is the capacity of a condenser that retains one coulomb of charge with one volt difference of potential.

Gauss:—From Carl F. Gauss (1785–1855). The C. G. S. unit of flux-density, or the unit by which the intensity of magnetic fields are measured. It equals one weber per normal square centimetre.

Gilbert:—The unit for measuring magneto-motive force, being produced by .7958 ampere-turn approximately.

Henry:—From Joseph Henry, of the Smithsonian Institution, Washington, D. C. The practical unit for measuring the induction in a circuit when the electro-motive force induced is one international volt, while the inducing current varies at the rate of one ampere per second.

Joule:—The C. G. S. unit of practical energy, being equivalent to the work done in keeping up for one second a current of one ampere against a resistance of one ohm. Named from J. P. Joule, of England.

Oersted:—From Oersted, the electrician. It is the practical unit for measuring electrical reluctance.

Watt:—The practical electrical unit of the rate of working in a circuit, when the electro-motive force is one volt, and the intensity of current is one ampere. It is equal to 107 ergs per second, or .00134 horse-power per second. Named from James Watt, of Scotland.

Weber:—The practical unit for measuring magnetic flux. Named from W. Weber, of Germany.

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