Beacon Lights of History Volume Xiv Part 15

Faraday did not seem to thoroughly understand this phenomenon. He spoke as if he thought the lines of magnetic force had been rendered luminous by the light rays; for, he announced his discovery in a paper ent.i.tled, "Magnetization of Light and the Illumination of the Lines of Magnetic Force." Indeed, this discovery was so far ahead of the times that it was not until a later date that the results were more fully developed, first by Kelvin, and subsequently by Clerk Maxwell. In 1865, two years before Faraday's death, Maxwell proposed the electro-magnetic theory of light, showing that light is an electro-magnetic disturbance. He pointed out that optical as well as electro-magnetic phenomena required a medium for their propagation, and that the properties of this medium appeared to be the same for both. Moreover, the rate at which light travels is known by actual measurement; the rate at which electro-magnetic waves are propagated can be calculated from electrical measurements, and these two velocities exactly agree. Faraday's original experiment as to the relation between light and magnetism is thus again experimentally demonstrated; and, Maxwell's electro-magnetic theory of light now resting on experimental fact, optics becomes a branch of electricity. A curious consequence was pointed out by Maxwell as a result of his theory; namely, that a necessary relation exists between opacity and conductivity, since, as he showed, electro-magnetic disturbances could not be propagated in substances which are conductors of electricity. In other words, if light is an electro-magnetic disturbance, all conducting substances must be opaque, and all good insulators transparent. This we know to be the fact: metallic substances, the best of conductors, are opaque, while gla.s.s and crystals are transparent. Even such apparent exceptions as vulcanite, an excellent insulator, fall into the law, since, as Graham Bell has recently shown, this substance is remarkably transparent to certain kinds of radiant energy.

In 1778, Brugmans of Leyden noticed that if a piece of bis.m.u.th was held near either pole of a strong magnet, repulsion occurred. Other observers noticed the same effect in the case of antimony. These facts appear to have been unknown to Faraday, who, in 1845, by employing powerful electro-magnets rediscovered them, and in addition showed that practically all substances possess the power of being attracted or repelled, when placed between the poles of sufficiently powerful magnets. By placing slender needles of the substances experimented on between the poles of powerful horse-shoe magnets, he found that they were all either attracted like iron, coming to rest with their greatest length extending between the poles; or, like bis.m.u.th, were apparently repelled by the poles, coming to rest at right angles to the position a.s.sumed by iron. He regarded the first cla.s.s of substances as attracted, and the second cla.s.s as repelled, and called them respectively paramagnetic and diamagnetic substances. In other words, paramagnetic substances, like iron, came to rest axially (extending from pole to pole), and diamagnetic substances, like bis.m.u.th, equatorially (extending transversely between the poles). He reserved the term magnetic substances to cover the phenomena of both para and dia-magnetism. He communicated the results of this investigation to the Royal Society in a paper on the "Magnetic Condition of All Matter," on Dec. 18, 1845.

The properties of paramagnetism and diamagnetism are not possessed by solids only, but exist also in liquids and gases. When experimenting with liquids, they were placed in suitable gla.s.s vessels, such as watch crystals, supported on pole pieces properly shaped to receive them.

Under these circ.u.mstances paramagnetic liquids, such as salts of iron or cobalt dissolved in water, underwent curious contortions in shape, the tendency being to arrange the greater part of their ma.s.s in the direction in which the flux pa.s.sed; namely, directly between the poles.

Diamagnetic liquids, such as solutions of salts of bis.m.u.th and antimony, in a similar manner, arranged the greater part of their ma.s.s in positions at right angles to this direction, or equatorially.

At first Faraday attributed the repulsion of diamagnetic substances to a polarity, separate and distinct from ordinary magnetic polarity, for which he proposed the name, diamagnetic polarity. He believed that when a diamagnetic substance is brought near to the north pole of a magnet, a north pole was developed in its approached end, and that therefore repulsion occurred. He afterwards rejected this view, though it has been subsequently adopted by Weber and Tyndall, the latter of whom conducted an extended series of experiments on the subject. The majority of physicists, however, at the present time, do not believe in the existence of a diamagnetic polarity. They point out that the apparent repulsion of diamagnetic substances is due to the fact that they are less paramagnetic than the oxygen of the air in which they are suspended.

During this investigation Faraday observed some phenomena that led him to a belief in the existence of another form of force, distinct from either paramagnetic or diamagnetic force, which he called the magne-crystallic force. He had been experimenting with some slender needles of bis.m.u.th, suspending them horizontally between the poles of an electro-magnet. Taking a few of these cylinders at random from a greater number, he was much perplexed to find that they did not all come to rest equatorially, as well-behaved bars of diamagnetic bis.m.u.th should do, though, if subjected to the action of a single magnetic pole, they did show this diamagnetic character by their marked repulsion. After much experimentation, he ascribed this phenomenon to the crystalline condition of the cylinder. By experimenting with carefully selected groups of crystals of bis.m.u.th, he believed he could trace the cause of the phenomenon to the action of a force which he called the magne-crystallic force.

Extended experiments carried on by Plucker on the influence of magnetism on crystalline substances led him to believe that a close relation exists between the ultimate forms of the particles of matter and their magnetic behavior. This subject is as yet far from being fully understood.

There was another series of investigations made by Faraday between the years 1831 and 1840, that has been wonderfully utilized, and may properly be ranked among his great discoveries. We allude to his researches on the laws which govern the chemical decomposition of compound substances by electricity. The fact that the electric current possesses the power of decomposing compound substances was known as early as 1800, when Carlisle and Nicholson separated water into its const.i.tuent elements, by the pa.s.sage of a voltaic current. Davy, too, in 1806, had delivered his celebrated discourse "On Some Chemical Agencies of Electricity," and in 1807, had announced his great discovery of the decomposition of the fixed alkalies.

Faraday showed that the amount of chemical action produced by electricity is fixed and definite. In order to be able to measure the amount of this action, he invented an instrument which he called a voltameter, or a volta-electrometer. It consisted of a simple device for measuring the amount of hydrogen and oxygen gases liberated by the pa.s.sage of an electric current through water acidulated with sulphuric acid. He showed, by numerous experiments, that the decomposition effected is invariably proportional to the amount of electricity pa.s.sing; that variations in the size of the electrodes, in the pressure, or in the degree of dilution of the electrolyte, had nothing to do with the result, and that therefore a voltameter could be employed to determine the amount of electricity pa.s.sing in a given circuit. He also demonstrated that when a current is pa.s.sed through different electrolytes (compound substances decomposed by the pa.s.sage of electricity), the amount of the decompositions are chemically equivalent to each other.

The extent of Faraday's work in the electro-chemical field may be judged by considering some of the terms he proposed for its phenomena, most of which, with some trifling exceptions, are still in use. It was he who gave the name electrolysis to decomposition by the electric current; he also proposed to call the wires, or conductors connected with the battery, or other electric source, the electrodes, naming that one which was connected with the positive terminal, the anode, and that one connected with the negative terminal, the cathode. He called the separate atoms or groups of atoms into which bodies undergoing electrolysis are separated, the radicals, or ions, and named the electro-positive ions, which appear at the cathode, the kathions, and the electro-negative radicals which appear at the anode, the anions.

There were many other researches made by Faraday, such as his experiments on disruptive electric discharges, his investigations on the electric eel, his many researches on the phenomena both of frictional electricity and of the voltaic pile, his investigations on the contact and chemical theories of the voltaic pile, and those on chemical decomposition by frictional electricity; these are but some of the mere important of them. Those we have already discussed will, however, amply suffice to show the value of his work. Rather than take up any others, let us inquire what influence, if any, the various groups of discoveries we have already discussed have exerted on the electric arts and sciences in our present time. What practical results have attended these discoveries? What actual, useful, commercial machines have been based on them? What useful processes or industries have grown out of them?

And, first, as to actual commercial machines. These researches not only led to the production of dynamo-electric machines, but, in point of fact, Faraday actually produced the first dynamo. A dynamo-electric machine, as is well known, is a machine by means of which mechanical energy is converted into electrical energy, by causing conductors to cut through, or be cut through by, lines of magnetic force; or, briefly, it is a machine by means of which electricity is readily obtained from magnetism.

Faraday's invention of the first dynamo is interesting because at the same time he made the invention he solved a problem which up to his time had been the despair of the ablest physicists and mathematicians. This was the phenomenon of Arago's rotating disc. It was briefly as follows: If a copper disc be rotated above a magnet, the needle tends to follow the plate in its rotation; or, if a copper plate be placed at rest above or below an oscillating magnet, it tends to check its oscillations and bring the needle quickly to rest. Faraday investigated these phenomena and soon discovered that a copper disc rotated below two magnet poles had electric currents generated in it, which flowed radially through the disc between its circ.u.mference and centre. By placing one end of a conducting circuit on the axis of the disc, and the other end on its circ.u.mference, he succeeded in drawing off a continuous electric current generated from magnetism, and thus produced the first dynamo. This was in 1831. Faraday produced many other dynamos besides this simple disc machine.

Although the disc dynamo in its original form was impracticable as a commercial machine, yet it was not only the forerunner of the dynamo, but was, in point of fact, the first machine ever produced that is ent.i.tled to be called a dynamo. He generously left to those who might come after him the opportunity to avail themselves of his wonderful discovery. "I have rather, however," he says, "been desirous of discovering new facts and new relations dependent on magneto-electric induction than of exalting the force of those already obtained, being a.s.sured that the latter would find their development hereafter." How profoundly prophetic! Could the ill.u.s.trious investigator see the hundreds of thousands of dynamos that are to-day in all parts of the world engaged in converting millions of horse-power of mechanical energy into electric energy, he would appreciate how marvellously his successors have "exalted the force" of some of the effects he had so ably shown the world how to obtain.

Faraday lived to see his infant dynamo, the first of its kind, developed into a machine not only sufficiently powerful to maintain electric arc lights, but also into a form sufficiently practicable to be continuously engaged in producing such light, in one of the lighthouses on the English coast. Holmes produced such a machine in 1862, or some years before Faraday's death. It was installed under the care of the Trinity House, at the Dungeness Lighthouse, in June, 1862, and continued in use for about ten years. When this machine was shown to Faraday by its inventor, the veteran philosopher remarked, "I gave you a baby, and you bring me a giant."

The alternating-current transformer is another gift of Faraday to the commercial world. As is well known, this instrument is a device for raising or lowering electric pressure. The name is derived from the fact that the instrument is capable of taking in at one pressure the electric energy supplied to it, and giving it out at another pressure, thus transforming it. Faraday produced the first transformer during his investigations on voltaic-current induction. The modern alternating-current transformer, though differing markedly in minor details from Faraday's primitive instrument, yet in general details is essentially identical with it. The enormous use of both step-up and step-down transformers--transformers which respectively induce currents of higher and of lower electromotive forces in their secondary coils than are pa.s.sed through their primaries--shows the great practical value of this invention. The wonderful growth of the commercial applications of alternating currents during the past few decades would have been impossible without the use of the alternating-current transformer.

It is an interesting fact that it was not in the form of the step-down alternating-current transformer that Faraday's discovery of voltaic-current induction was first utilized, but in the form of a step-up transformer, or what was then ordinarily called an induction coil. As early as 1842, Ma.s.son and Breguet constructed an induction coil by means of which minute sparks could be obtained from the secondary, in vacuo. In 1851, Ruhmkorff constructed an induction coil so greatly improved, by the careful insulation of its secondary circuit, that he could obtain from it torrents of long sparks in ordinary air.

The Ruhmkorff induction coil has in late years been greatly improved both by Tesla and Elihu Thomson, who, separately and independently of each other, have produced excellent forms of high-frequency induction coils.

Induction coils have long been in use for purposes of research, and in later years have been employed in the production both of the Rontgen rays used in the photography of the invisible, and the electro-magnetic waves used in wireless telegraphy.

Rontgen's discovery was published in 1895. It was rendered possible by the prior work of Geissler and Crookes on the luminous phenomena produced by the pa.s.sage of electric discharges through high vacua in gla.s.s tubes. Rontgen discovered that the invisible rays, or radiation, emitted from certain parts of a high-vacuum tube, when high-tension discharges from induction coils were pa.s.sing, possessed the curious property of traversing certain opaque substances as readily as light does gla.s.s or water. He also discovered that these rays were capable of exciting fluorescence in some substances,--that is, of causing them to emit light and become luminous,--and that these rays, like the rays of light, were capable of affecting a photographic plate. From these properties two curious possibilities arose; namely, to see through opaque bodies, and to photograph the invisible. Rontgen called these rays X, or unknown rays. They are now almost invariably called by the name of their distinguished discoverer.

Let us briefly investigate how it is possible both to see and to photograph the invisible. Shortly after Rontgen's discovery, Edison, with that wonderful power of finding practical applications for nearly all discoveries, had invented the fluoroscope,--a screen covered with a peculiar chemical substance that becomes luminous when exposed to the Rontgen rays. Suppose, now, between the rays and such a screen be interposed a substance opaque to ordinary light, as, for example, the human hand. The tissues of the hand, such as the flesh and the blood, permit the rays to readily pa.s.s through them, but the bones are opaque to the rays, and, therefore, oppose their pa.s.sage; consequently, the screen; instead of being uniformly illumined, will show shadows of the bones, so that, to an eye examining the screen, it will seem as though it were looking through the flesh and blood directly at the bones. In a similar manner, if a photographic plate be employed instead of the screen, a distinct photographic picture will be obtained.

Both the fluoroscope and the photographic camera have proved an invaluable aid to the surgeon, who can now look directly through the human body and examine its internal organs, and so be able to locate such foreign bodies as bullets and needles in its various parts, or make correct diagnoses of fractures or dislocations of the bones, or even examine the action of such organs as the liver and heart.

About 1886, Hertz discovered that if a small Leyden jar is discharged through a short and simple circuit, provided with a spark-gap of suitable length, a series of electro-magnetic waves are set up, which, moving through s.p.a.ce in all directions, are capable of exciting in a similar circuit effects that can be readily recognized, although the two circuits are at fairly considerable distances apart. Here we have a simple basic experiment in wireless telegraphy, which, briefly considered, consists of means whereby oscillations or waves, set up in free s.p.a.ce by means of disruptive discharges, are caused to traverse s.p.a.ce and produce various effects in suitably constructed receptive devices that are operated by the waves as they impinge on them.

At first a doubt was expressed by eminent scientific men as to the practicability of successfully transmitting wireless messages through long distances, since these waves, travelling in all directions, would soon become too attenuated to produce intelligible signals; but when it was shown, from theoretical considerations, that these waves when traversing great distances are practically confined to the s.p.a.ce between the earth's surface and the upper rarified strata of the atmosphere, the possibility of long-distance wireless telegraphic transmission was recognized. To increase the distance, it was only necessary either to increase the energy of the waves at the transmitting station, or to increase the delicacy of the receiving instruments, or both.

It has been but a short time since both the scientific and the financial worlds were astounded by the actual transmission of intelligible wireless signals across the Atlantic, and the name of Marconi will go down to posterity as the one who first accomplished this great feat.

The princ.i.p.al limit to the distance of transmission lies in the delicacy of the receiving instruments. The most sensitive are those in which a telephone receiver forms a part of the receiving apparatus. The almost incredibly small amount of electric energy required to produce intelligible speech in an ordinary Bell telephone receiver nearly pa.s.ses belief. The work done in lifting such an instrument from its hook to the ear of the listener, would, if converted into electric energy, be sufficient to maintain an audible sound in a telephone for 240,000 years! Even extremely attenuated waves may therefore produce audible signals in such a receiver.

The electric motor was another gift of Faraday to commercial science, although in this case there are others who can, perhaps, justly claim to share the honor with him. Faraday's early electric motor consisted essentially in a device whereby a movable conductor, suspended so as to be capable of rotation around a magnet pole, was caused to rotate by the mutual interaction of the magnetic fields of the active conductor and the magnet. The magnet, which consisted of a bar of hardened steel, was fixed in a cork stopper, which completely closed the end of an upright gla.s.s tube. A small quant.i.ty of mercury was placed in the lower end of the tube, so as to form a liquid contact for the lower end of a movable wire, suspended so as to be capable of rotating at its lower extremity about the axis of the tube. On the pa.s.sage of an electric current through the wire, a continuous rotary motion was produced in it, the direction of which depends both on the direction of the current, and on the polarity of the end of the magnet around which the rotation occurs.

The great value of the electric motor to the world is too evident to need any proof. The number of purposes for which electric motors are now employed is so great that the actual number of motors in daily use is almost incredible, and every year sees this number rapidly increasing.

The above are the more important machines or devices that have been directly derived from Faraday's great investigation as to the production of electricity from magnetism. Let us now inquire briefly as to what useful processes or industries have been rendered possible by the existence of these machines.

Apparently one of the most marked requirements of our twentieth-century civilization is that man shall be readily able to extend the day far into the night. He can no longer go to sleep when the sun sets, and keep abreast with his compet.i.tors. Of all artificial illuminants yet employed, the arc and the incandescent electric lights are unquestionably the best, whether from a sanitary, aesthetic, or truest economical standpoint. Now, while it is a well-known matter of record that both arc and incandescent lights were invented long before Faraday's time, yet it was not until a source of electricity was invented, superior both in economy and convenience to the voltaic battery, that either of these lights became commercial possibilities.

Such an electric source was given to the world by Faraday through his invention of the dynamo-electric machine, and it was not until this machine was sufficiently developed and improved that commercial electric lighting became possible. The energy of burning coal, through the steam-engine, working the dynamo, is far cheaper and more efficient for producing electricity than the consumption of metals through the voltaic pile.

It is characteristic of the modesty of Faraday that when, in after-life, he heard inventors speaking of their electric lights, he refrained from claiming the electric light as his own, although, without the machine he taught the world how to construct, commercial lighting would have been an impossibility.

The marvellous activity in the electric arts and sciences, which followed as a natural result of Faraday giving to the world in the dynamo-electric machine a cheap electric source, naturally leads to the inquiry as to whether at a somewhat later day a yet greater revolution may not follow the production of a still cheaper electric source. In point of fact such a discovery is by no means an impossibility. When a dynamo-electric machine is caused to produce an electric current by the intervention of a steam-engine, the transformation of energy which takes place from the energy of the coal to electric energy is an extremely wasteful one. Could some practical method be discovered by means of which the burning of coal liberates electric energy, instead of heat energy, an electric source would be discovered that would far exceed in economy the best dynamo in existence. With such a discovery what the results would be no one can say; this much is certain, that it would, among other things, relegate the steam-engine to the sc.r.a.p-heap, and solve the problem of aerial navigation.

What is justly regarded as one of the greatest achievements of modern times is the electrical transmission of power over comparatively great distances. At some cheap source of energy, say, at a waterfall, a water-wheel is employed to drive a dynamo or generator, thus converting mechanical energy into electrical energy. This electricity is pa.s.sed over a conducting line to a distant station, where it is either directly utilized for the purpose of lighting, heating, chemical decomposition, etc., or indirectly utilized for the purpose of obtaining mechanical power for driving machinery, by pa.s.sing it through an electric motor.

The electric transmission of power has been successfully made in California over a distance of some 220 miles, at a pressure on transmission lines of 50,000 volts.

The high pressures required for the economical use of transmission lines necessitates the employment of transformers at each end of the line; namely, step-up transformers at the transmitting end, to raise the voltage delivered by the generators, and step-down transformers, at the receiving end, to lower it for use in the various translating devices.

These transformers are employed in connection with alternating-current dynamos. Faraday not only gave to the world the first electric generator, but also the first transformer, and one of the first electric motors, and without these gifts the electric transmission of power over long distances, which has justly been regarded as one of the most marvellous achievements of our age, would have been an impossibility.

In high-tension circuits over which such pressures as 50,000 volts is transmitted, no little difficulty is experienced from leakage and consequent loss of energy. This leakage occurs both between the line conductors and at the insulators placed on the pole lines forming the line circuit. The insulators are made either of gla.s.s or porcelain, and are of a peculiar form known as triple petticoat pattern. The loss on such lines, due to leakage between wires, is greater than that which takes place at the pole insulators, and is diminished by keeping the circuit wires as far apart as possible.

In the early history of the art, electric transmission of power was effected by means of direct-current generators and motors,--generators and motors through which the current always pa.s.sed in the same direction. Such generators and motors, however, possessed inconveniences that prevented extensive commercial transmission of power, since, as we have seen, high pressure was necessary for efficiency in such transmission, and the collecting-brushes and commutators employed in all direct-current generators and motors to carry the current from the machine or to the motor, were a constant source of trouble and danger.

When the alternating-current motor first same into general use, it was employed, in connection with the alternating-current generator, in electric transmission systems; but such motors also possess the inconvenience of not readily starting from a state of rest, with their full turning power, or torque, and of therefore being unsuitable where the motor requires to be frequently stopped or started. Had these difficulties remained unsolved, long-distance electric transmission of power, so successful in operation to-day, and which bids fair to be still more successful in the near future, would have been impossible.

Fortunately, these difficulties were overcome by the genius of Nikola Tesla, in the invention of the multiphase alternating-current motor, or the induction motor, as it is now generally called. Although Baily, Deprez, and Ferraris had accomplished much before Tesla's time, yet it was practically to the investigations and discoveries made by Tesla, between 1887 and 1891, that the induction motor of to-day is due.

Another requirement of our twentieth-century civilization is rapid transit, either urban or inter-urban, and this is afforded by various systems of electric street railways or electric traction generally, including electric locomotives and electric automobiles. The wonderful growth in this direction which has been witnessed in the last few decades would have been impossible without the electric generator and motor, both gifts of Faraday to the world. Their application in this direction must, therefore, go to swell the debt our civilization owes to the labors of this great investigator.

In the system of electric street-car propulsion very generally employed to-day, a single trolley wheel is employed for taking the driving current from an overhead conductor, suspended above the street. The trolley wheel is supported by a trolley pole, and is maintained in good electric contact with the trolley wire, or overhead conductor. By this means the current pa.s.ses from the wire down the conductor connected with the trolley pole, thence through the motors placed below the body of the car, and from them, through the track or ground-return, back to the power station. A small portion of the current is employed for lighting the electric lamps in the car. In some systems an underground trolley is employed.

An important device, called the series-parallel controller, is employed in all systems of electric street-car propulsion. It consists of means by which the starting and stopping of the car, and changes, both in its speed and direction, are placed under the control of the motorman. A separate controller is placed on both platforms of the car. The series-parallel controller consists essentially of a switch by means of which the several motors, that are employed in all street cars, can be variously connected with each other, or with different electric resistances, or can be successively cut out or introduced into the circuit, so that the speed of the car can be regulated at will, as the handle of the controller is moved by the motorman to the various notches on the top of the controller box. As generally arranged, the speed increases from the first notch or starting position to the last notch, movements in the opposite direction changing connections in the opposite order of succession, and, therefore, slowing the car. There is, however, no definite speed corresponding to each notch, for this will vary with the load on each car, and with the gradient upon which it may be running.

But there is another valuable gift received by the world as a result of this great discovery of Faraday; namely, that most marvellous instrument of modern times, the speaking telephone. This instrument was invented in 1861, by Philip Ries, and subsequently independently reinvented in 1876, by Elisha Gray and Alexander Graham Bell.

As is well known, it is electric currents and not sound-waves that are transmitted over a telephone circuit. The magneto-electric telephone in its simplest form consists of a pair of instruments called respectively the transmitter and the receiver. We talk into the transmitter and listen at the receiver. Both transmitter and receiver consist of a permanent magnet of hardened steel around one end of which is placed a coil of insulated wire. In front of this coil a diaphragm, or thin plate, of soft iron, is so supported as to be capable of freely vibrating towards and from the magnet pole.

The operation of the transmitting instrument is readily understood in the light of Faraday's discovery. It is simply a dynamo-electric machine driven by the voice of the speaker. As the sound-waves from the speaker's voice strike against the diaphragm, which has become magnetic from its nearness to the magnet pole, electric currents are generated in the coil of wire surrounding such pole, since the to-and-fro motions cause the lines of electro-magnetic force to pa.s.s through the wire on the moving coil. The operation of the receiving instrument is also readily understood. It acts as an electric motor driven by the to-and-fro currents generated by the transmitter. As these currents are transmitted over the wire, they pa.s.s through the coil of wire on the receiving instrument, and reproduce therein the exact movements of the transmitting diaphragm, since, as they strengthen or weaken the magnetism of the pole, they cause similar motions in the diaphragm placed before it. Consequently, one listening at the receiving diaphragm will hear all that is uttered into the transmitting diaphragm. It was thus, by the combination of the dynamo and motor, both of which were given by Faraday to the world, that we have received this priceless instrument, which has been so potent in its effects on the civilization of the Twentieth century.

The electric telegraph had its beginnings long before Faraday's time. As early as 1847, Watson had erected a line some two miles in length, extending over the housetops in London, and operated it by means of discharges from an ordinary frictional electric machine. In 1774, Lesage had erected in Geneva an electric telegraph consisting of a number of metallic wires, one for each letter of the alphabet. These wires were carefully insulated from each other. When a message was to be sent over this early telegraphic line an electric discharge was pa.s.sed through the particular wire representing the letter of the alphabet to be sent; this discharge, reaching the other end, caused a pithball to be repelled and thus laboriously, letter by letter, the message was transmitted. How ludicrously c.u.mbersome was such an instrument when contrasted with the Morse electro-magnetic telegraph of to-day, which requires but a single wire; or with the harmonic telegraph of Gray, which permits the simultaneous transmission of eight or more separate messages over a single wire; or with the wonderful quadruplex telegraphic system of Edison which permits the simultaneous transmission of four separate and distinct messages over a single wire, two in one direction, and two in the opposite direction at the same time; or with the still more wonderful multiplex telegraph of Delaney, which is able to simultaneously transmit as many as seventy-two separate messages over a single wire, thirty-six in one direction and thirty-six in the opposite direction. These achievements have been possible only through the researches and discoveries of Oersted, Faraday, and hosts of other eminent workers; for, it was the electro-magnet, rendered possible by Oersted, together with the magnificent discoveries of Faraday, and others since his time, that these marvellous advances in electro-telegraphic transmission of intelligence have become possibilities.

Before completing this brief sketch of some of the effects that Faraday's work has had on the practical arts and sciences, let us briefly examine the generating plants that are either in operation or construction at Niagara Falls.

Some idea of the size of the Niagara Falls generating plant on the American side may be gained from the fact that there have already been installed eleven of the separate 5,000 horse-power generators. The remaining capacity of the tunnel will permit of the installation of 50,000 additional horse-power, or 105,000 horse-power in all.

On the Canadian side of the Falls another great plant is about to be erected with an ultimate capacity of several hundred thousand horse-power. Here, however, the size of the generating unit will be double that on the American side, or 10,000 horse-power. These generators will be wound to produce an electric pressure of 12,000 volts, raised by means of step-up transformers to 22,000, 40,000, and 60,000 volts, according to the distance of transmission. Each of the revolving parts of these machines will weigh 141,000 pounds. To what gigantic proportions has the little infant dynamo of Faraday grown in this short time since its birth!

The low rates at which electric power can be sold in the immediate neighborhood of the Niagara generating plant have naturally resulted in an enormous growth of the electro-chemical industries, for these industries could never otherwise develop into extended commercial applications. Of the total output of, say, 55,000 horse-power at the Niagara Falls generating plant, no less than 23,200 horse-power is used in various electrolytic and electro-thermal processes in the immediate neighborhood. Some of the more important consumers of the electric power, named in the order of consumption, are for the manufacture of the following products: calcium carbide, aluminium, caustic soda and bleaching salt, carborundum, and graphite.

Calcium carbide, employed in the production of acetylene gas, either for the purposes of artificial illumination, or for the manufacture of ethyl alcohol, is produced by subjecting a mixture of carbon and lime to the prolonged action of heat in an electric furnace.