These automatic or self-acting fire-alarms can, of course, be connected in the circuit of the ordinary street fire-alarms, which are usually worked by pulling a handle to make the necessary contact.

From what has been said, it will be easy to understand how the stealthy entrance of burglars into a house can be announced by an electric bell or warning lamp. If press-buttons or contact-keys are placed on the sashes of the windows, the posts of the door, or the treads of the stair, so that when the window or door is opened, or the tread bends under the footstep, an electric circuit is closed, the alarm will be given. Of course, the connections need only be arranged when the device is wanted. Shops and offices can be guarded by making the current show a red light from a lamp hung in front of the premises, so that the night watchman can see it on his beat. This can readily be done by adjusting an electromagnet to drop a screen of red glass before the flame of the lamp. Safes and showcases forcibly opened can be made to signal the fact, and recently in the United States a thief was photographed by a flashlight kindled in this way, and afterwards captured through the likeness.

The level of water in cisterns and reservoirs, can be told in a similar manner by causing a float to rise with the water and make the required contact. The degree of frost in a conservatory can also be announced by means of the mercury "thermostat," already described, or some equivalent device. There are, indeed, many actual or possible applications of a similar kind.

The Massey log is an instrument for telling the speed of a ship by the revolutions of a "fly" as it is towed through the water, and by making the fly complete a circuit as it revolves the number of turns a second can be struck by a bell on board. In one form of the "electric log," the current is generated by the chemical action of zinc and copper plates attached to the log, and immersed in the sea water, and in others provided by a battery on the ship.

Captain M'Evoy has invented an alarm for torpedoes and torpedo boats, which is a veritable watchdog of the sea. It consists of an iron bell-jar inverted in the water, and moored at a depth below the agitation of the waves. In the upper part of the jar, where the pressure of the air keeps back the water, there is a delicate needle contact in circuit with a battery and an electric bell or lamp, as the case may be, on the shore. Waves of sound passing through the water from the screw propeller of the torpedo, or, indeed, any ship, make and break the sensitive contact, and ring the bell or light the lamp. The apparatus is intended to alarm a fleet lying at anchor or a port in time of war.

Electricity has also been employed to register the movements of weathercocks and anemometers. A few years ago it was applied successfully to telegraph the course marked by a steering compass to the navigating officer on the bridge. This was done without impeding the motion of the compass card by causing an electric spark to jump from a light pointer on the card to a series of metal plates round the bowl of the compass, and actuate an electric alarm.

The "Domestic Telegraph," an American device, is a little dial apparatus by which a citizen can signal for a policeman, doctor, messenger, or carriage, as well as a fire engine, by the simple act of setting a hand on the dial.

Alexander Bain was the first to drive a clock with electricity instead of weights, by employing a pendulum having an iron bob, which was attracted to one side and the other by an electromagnet, but as its rate depends on the constancy of the current, which is not easy to maintain, the invention has not come into general use. The "butterfly clock" of Lemoine, which we illustrate in figure 89, is an improved type, in which the bob of soft iron P swings to and fro over the poles of a double electro magnet M in circuit with a battery and contact key. When the rate is too slow the key is closed, and a current passing through the electromagnet pulls on the pendulum, thus correcting the clock. This is done by the ingenious device of Hipp, shown in figure 90, where M is the electromagnet, P the iron bob, from which projects a wire bearing a light vane B of mica in the shape of a butterfly. As the bob swings the wire drags over the hump of the metal spring S, and when the bob is going too slowly the wire thrusts the spring into contact with another spring T below, thus closing the circuit, and sending a current through the magnet M, which attracts the bob and gives a fillip to the pendulum.

Local clocks controlled from a standard clock by electricity have been more successful in practice, and are employed in several towns—for example, Glasgow. Behind local dials are electromagnets which, by means of an armature working a frame and ratchet wheel, move the hands forward every minute or half-minute as the current is sent from the standard clock.

The electrical chronograph is an instrument for measuring minute intervals of time by means of a stylus tracing a line on a band of travelling paper or a revolving barrel of smoked glass. The current, by exciting an electromagnet, jerks the stylus, and the interval between two jerks is found from the length of the trace between them and the speed of the paper or smoked surface. Retarded clocks are sometimes employed as electric meters for registering the consumption of electricity. In these the current to be measured flows through a coil beneath the bob of the pendulum, which is a magnet, and thus affects the rate. In other meters the current passes through a species of galvanometer called an ampere meter, and controls a clockwork counter. In a third kind of meter the chemical effect of the current is brought into play— that of Edison, for example, decomposing sulphate of copper, or more commonly of zinc.

The electric light is now used for signalling and advertising by night in a variety of ways. Incandescent lamps inside a translucent balloon, and their light controlled by a current key, as in a telegraph circuit, so as to give long and short flashes, according to the Morse code, are employed in the army. Signals at sea are also made by a set of red and white glow-lamps, which are combined according to the code in use. The powerful arc lamp is extremely useful as a "search light," especially on men of war and fortifications, and it has also been tried in signalling by projecting the beam on the clouds by way of a screen, and eclipsing it according to a given code.

In 1879, Professor Graham Bell, the inventor of the speaking telephone, and Mr Summer Tamter, brought out an ingenious apparatus called the photophone, by which music and speech were sent along a beam of light for several hundred yards. The action of the photophone is based on the peculiar fact observed in 1873 by Mr J E Mayhew, that the electrical resistance of crystalline selenium diminishes when a ray of light falls upon it. Figure 91 shows how Bell and Tamter utilised this property in the telephone. A beam of sun or electric light, concentrated by a lens L, is reflected by a thin mirror M, and after traversing another lens L, travels to the parabolic reflector R, in the focus of which there is a selenium resistance in circuit with a battery S and two telephones T T'. Now, when a person speaks into the tube at the back of the mirror M, the light is caused to vibrate with the sounds, and a wavering beam falls on the selenium, changing its resistance to the current. The strength of the current is thus varied with the sonorous waves, and the words spoken by the transmitter are heard in the telephones by the receiver. The photophone is, however, more of a scientific toy than a practical instrument.

Becquerel, the French chemist, found that two plates of silver freshly coated with silver from a solution of chloride of silver and plunged into water, form a voltaic cell which is sensitive to light. This can be seen by connecting the plates through a galvanometer, and allowing a ray of light to fall upon them. Other combinations of the kind have been discovered, and Professor Minchin, the Irish physicist, has used one of these cells to measure the intensity of starlight.

The "induction balance" of Professor Hughes is founded on the well-known fact that a current passing in one wire can induce a sympathetic current in a neighbouring wire. The arrangement will be understood from figure 92, where P and P1 are two similar coils or bobbins of thick wire in circuit with a battery B and a microphone M, while S and S1 are two similar coils or bobbins of fine wire in circuit with a telephone T. It need hardly be said that when the microphone M is disturbed by a sound, the current in the primary coils P P1 will induce a corresponding current in the secondary coils S S1; but the coils S S1 are so wound that the induction of P on S neutralises the induction of P1 on S1; and no current passes in the secondary circuit, hence no sound is heard in the telephone. When, however, this balance of induction is upset by bringing a piece of metal—say, a coin—near one or other of the coils S S1, a sound will be heard in the telephone.

The induction balance has been used as a "Sonometer" for measuring the sense of hearing, and also for telling base coins. The writer devised a form of it for "divining" the presence of gold and metallic ores which has been applied by Captain M'Evoy in his "submarine detector" for exploring the sea bottom for lost anchors and sunken treasure. When President Garfield was shot, the position of the bullet was ascertained by a similar arrangement.

The microphone as a means of magnifying feeble sounds has been employed for localising the leaks in water pipes and in medical examinations. Some years ago it saved a Russian lady from premature burial by rendering the faint beating of her heart audible.

Edison's electric pen is useful in copying letters. It works by puncturing a row of minute holes along the lines of the writing, and thus producing a stencil plate, which, when placed over a clean sheet of paper and brushed with ink, gives a duplicate of the writing by the ink penetrating the holes to the paper below. It is illustrated in figure 93, where P is the pen, consisting of a hollow stem in which a fine needle actuated by the armature of a small electromagnet plies rapidly up and down and pierces the paper. The current is derived from a small battery B, and an inking roller like that used in printing serves to apply the ink.

In 1878 Mr. Edison announced his invention of a machine for the storage and reproduction of speech, and the announcement was received with a good deal of incredulity, notwithstanding the partial success of Faber and others in devising mechanical articulators. The simplicity of Edison's invention when it was seen and heard elicited much admiration, and although his first instrument was obviously imperfect, it was nevertheless regarded as the germ of something better. If the words spoken into the instrument were heard in the first place, the likeness of the reproduction was found to be unmistakable. Indeed, so faithful was the replica, that a member of the Academy of Sciences, Paris, stoutly maintained that it was due to ventriloquism or some other trickery. It was evident, however, that before the phonograph could become a practical instrument, further improvements in the nicety of its articulation were required. The introduction of the electric light diverted Mr. Edison from the task of improving it, although he does not seem to have lost faith in his pet invention. During the next ten years he accumulated a large fortune, and was the principal means of introducing both electric light and power to the world at large. This done, however, he returned to his earlier love, and has at length succeeded in perfecting it so as to redeem his past promises and fulfill his hopes regarding it.

The old instrument consisted, as is well known, of a vibrating tympan or drum, from the centre of which projected a steel point or stylus, in such a manner that on speaking to the tympan its vibrations would urge the stylus to dig into a sheet of tinfoil moving past its point. The foil was supported on a grooved barrel, so that the hollow of the groove behind it permitted the foil to give under the point of the stylus, and take a corrugated or wavy surface corresponding to the vibrations of the speech. Thus recorded on a yielding but somewhat stiff material, these undulations could be preserved, and at a future time made to deflect the point of a similar stylus, and set a corresponding diaphragm or tympan into vibration, so as to give out the original sounds, or an imitation of them.

Tinfoil, however, is not a very satisfactory material on which to receive the vibrations in the first place. It does not precisely respond to the movements of the marking stylus in taking the impression, and does not guide the receiving stylus sufficiently well in reproducing sounds. Mr. Edison has therefore adopted wax in preference to it; and instead of tinfoil spread on a grooved support, he now employs a cylinder of wax to take the print of the vibrations. Moreover, he no longer uses the same kind of diaphragm to print and receive the sounds, but employs a more delicate one for receiving them. The marking cylinder is now kept in motion by an electric motor, instead of by hand-turning, as in the earlier instrument.

The new phonograph, which we illustrate in figure 94, is about the size of an ordinary sewing machine, and is of exquisite workmanship, the performance depending to a great extent on the perfection and fitness of the mechanism. It consists of a horizontal spindle S, carrying at one end the wax cylinder C, on which the sonorous vibrations are to be imprinted. Over the cylinder is supported a diaphragm or tympan T, provided with a conical mouthpiece M for speaking into. Under the tympan there is a delicate needle or stylus, with its point projecting from the centre of the tympan downwards to the surface of the wax cylinder, so that when a person speaks into the mouthpiece, the voice vibrates the tympan and drives the point of the stylus down into the wax, making an imprint more or less deep in accordance with the vibrations of the voice. The cylinder is kept revolving in a spiral path, at a uniform speed, by means of an electric motor E, fitted with a sensitive regulator and situated at the base of the machine. The result is that a delicate and ridgy trace is cut in the surface of wax along a spiral line. This is the sound record, and by substituting a finer tympan for the one used in producing it, the ridges and inequalities of the trace can be made to agitate a light stylus resting on them, and cause it to set the delicate tympan into vibrations corresponding very accurately to those of the original sounds. The tympan employed for receiving is made of gold-beater's skin, having a stud at its centre and a springy stylus of steel wire. The sounds emitted by this device are almost a whisper as compared to the original ones, but they are faithful in articulation, which is the main object, and they are conveyed to the ear by means of flexible hearing-tubes.

These tympans are interchangeable at will, and the arm which carries them is also provided with a turning tool for smoothing the wax cylinder prior to its receiving the print. The cylinders are made of different sizes, from 1 to 8 inches long and 4 inches in diameter. The former has a storage capacity of 200 words. The next in size has twice that, or 400 words, and so on. Mr. Edison states that four of the large 8-inch cylinders can record all "Nicholas Nickleby," which could therefore be automatically read to a private invalid or to a number of patients in a hospital simultaneously, by means of a bunch of hearing-tubes. The cylinders can be readily posted like letters, and made to deliver their contents viva voce in a duplicate phonograph, every tone and expression of the writer being rendered with more or less fidelity. The phonograph has proved serviceable in recording the languages and dialects of vanishing races, as well as in teaching pronunciation.

The dimensions, form, and consequent appearance of the present commercial American phonograph are quite different from that above described, but the underlying principles and operations are identical.

A device for lighting gas by the electric spark is shown in figure 95, where A is a flat vulcanite box, containing the apparatus which generates the electricity, and a stem or pointer L, which applies the spark to the gas jet. The generator consists of a small "influence" machine, which is started by pressing the thumb- key C on the side of the box. The rotation of a disc inside the box produces a supply of static electricity, which passes in a stream of sparks between two contact-points in the open end of the stem D. The latter is tubular, and contains a wire insulated from the metal of the tube, and forming with the tube the circuit for the electric discharge. The handle enables the contrivance to be readily applied. The apparatus is one of the few successful practical applications of static electricity.

Other electric gas-lighters consist of metal points placed on the burner, so that the electric spark from a small induction coil or dynamo kindles the jet.

A platinum wire made white-hot by the passage of a current is sometimes used to light lamps, as shown in figure 96, where W is a small spiral of platinum connected in circuit with a generator by the terminals T T. When the lamp L is pressed against the button B the wire glows and lights it.

Explosives, such as gunpowder and guncotton, are also ignited by the electric spark from an induction coil or the incandescence of a wire. Figure 97 shows the interior of an ordinary electric fuse for blasting or exploding underground mines. It consists of a box of wood or metal primed with gunpowder or other explosive, and a platinum wire P soldered to a pair of stout copper wires W, insulated with gutta-percha. When the current is sent along these wires, the platinum glows and ignites the explosive. Detonating fuses are primed with fulminate of mercury.

Springs for watches and other purposes are tempered by heating them with the current and quenching them in a bath of oil.

Electrical cautery is performed with an incandescent platinum wire in lieu of the knife, especially for such operations as the removal of the tongue or a tumour.

It was known to the ancients that a fish called a torpedo existed in the Mediterranean which was capable of administering a shock to persons and benumbing them. The torpedo, or "electric ray," is found in the Atlantic as well as the Mediterranean, and is allied to the skate. It has an electric organ composed of 800 or 1000 polygonal cells in its head, and the discharge, which appears to be a vibratory current, passes from the back or positive pole to the belly or negative pole through the water. The gymotus, or Surinam eel, which attains a length of five or six feet, has an electric organ from head to tail, and can give a shock sufficient to kill a man. Humboldt has left a vivid picture of the frantic struggles of wild horses driven by the Indians of Venezuela into the ponds of the savannahs infested by these eels, in order to make them discharge their thunderbolts and be readily caught.

Other fishes—the silurus, malapterurus, and so on—are likewise endowed with electric batteries for stunning and capturing their prey. The action of the organs is still a mystery, as, indeed, is the whole subject of animal electricity. Nobili and Matteucci discovered that feeble currents are generated by the excitation of the nerves and the contraction of the muscles in the human subject.

Electricity promises to become a valuable remedy, and currents— continuous, intermittent, or alternating—are applied to the body in nervous and muscular affections with good effect; but this should only be done under medical advice, and with proper apparatus.

In many cases of severe electric shock or lightning stroke, death is merely apparent, and the person may be brought back to life by the method of artificial respiration and rhythmic traction of the tongue, as applied to the victims of drowning or dead faint.

A good lightning conductor should not have a higher electrical resistance than 10 ohms from the point to the ground, including the "earth" contact. Exceptionally good conductors have only about 5 ohms. A high resistance in the rod is due either to a flaw in the conductor or a bad earth connection, and in such a case the rod may be a source of danger instead of security, since the discharge is apt to find its way through some part of the building to the ground, rather than entirely by the rod. It is, therefore, important to test lightning conductors from time to time, and the magneto-electric tester of Siemens, which we illustrate in figures 98 and 99, is very serviceable for the purpose, and requires no battery. The apparatus consists of a magneto-electric machine AT, which generates the testing current by turning a handle, and a Wheatstone bridge. The latter comprises a ring of German silver wire, forming two branches. A contact lever P moves over the ring, and is used as a battery key. A small galvanometer G shows the indications of the testing current. A brass sliding piece S puts the galvanometer needle in and out of action. There are also several connecting terminals, b b', l, &c., and a comparison resistance R (figure 98). A small key K is fixed to the terminal l (figure 99), and used to put the current on the lightning-rod, or take it off at will. A leather bag A at one side of the wooden case (figure 99) holds a double conductor leading wire, which is used for connecting the magneto-electric machine to the bridge. On turning the handle of M the current is generated, and on closing the key K it circulates from the terminals of the machine through the bridge and the lightning-rod joined with the latter. The needle of the galvanometer is deflected by it, until the resistance in the box R is adjusted to balance that in the rod. When this is so, the galvanometer needle remains at rest. In this way the resistance of the rod is told, and any change in it noted. In order to effect the test, it is necessary to have two earth plates, E1 and E2, one (El) that of the rod, and the other (E2) that for connecting to the testing apparatus by the terminal b1 (figure 99). The whole instrument only weighs about 9 lbs. In order to test the "earth" alone, a copper wire should be soldered to the rod at a convenient height above the ground, and terminal screws fitted to it, as shown at T (figure 99), so that instead of joining the whole rod in circuit with the apparatus, only that part from T downwards is connected. The Hon. R. Abercrombie has recently drawn attention to the fact that there are three types of thunderstorm in Great Britain. The first, or squall thunderstorms, are squalls associated with thunder and lightning. They form on the sides of primary cyclones. The second, or commonest thunderstorms, are associated with secondary cyclones, and are rarely accompanied by squalls The third, or line thunderstorms, take the form of narrow bands of rain and thunder—for example, 100 miles long by 5 to 10 miles broad. They cross the country rapidly, and nearly broadside on. These are usually preceded by a violent squall, like that which capsized the Eurydice.

The gloom of January, 1896, with its war and rumours of war, was, at all events, relieved by a single bright spot. Electricity has surprised the world with a new marvel, which confirms her title to be regarded as the most miraculous of all the sciences. Within the past twenty years she has given us the telephone of Bell, enabling London to speak with Paris, and Chicago with New York; the microphone of Hughes, which makes the tread of a fly sound like the "tramp of an elephant," as Lord Kelvin has said; the phonograph of Edison, in which we can hear again the voices of the dead; the electric light which glows without air and underwater, electric heat without fire, electric power without fuel, and a great deal more beside. To these triumphs we must now add a means of photographing unseen objects, such as the bony skeletons in the living body, and so revealing the invisible.

Whether it be that the press and general public are growing more enlightened in matters of science, or that Professor Rontgen's discovery appeals in a peculiar way to the popular imagination, it has certainly evoked a livelier and more sudden interest than either the telephone, microphone, or phonograph. I was present when Lord Kelvin first announced the invention of the telephone to a British audience, and showed the instrument itself, but the intelligence was received so apathetically that I suspect its importance was hardly realised. It fell to my own lot, a few years afterwards, to publish the first account of the phonograph in this country, and I remember that, between incredulity on the one hand, and perhaps lack of scientific interest on the other, a considerable time elapsed before the public at large were really impressed by the invention. Perhaps the uncanny and mysterious results of Rontgen's discovery, which seem to link it with the "black arts," have something to do with the quickness of its reception by all manner of people.

Like most, if not all, discoveries and inventions, it is the outcome of work already done by other men. In the early days of electricity it was found that when an electric spark from a frictional machine was sent through a glass bulb from which the air had been sucked by an air pump, a cloudy light filled the bulb, which was therefore called an "electric egg". Hittorf and others improved on this effect by employing the spark from an induction coil and large tubes, highly exhausted of air, or containing a rare infusion of other gases, such as hydrogen. By this means beautiful glows of various colours, resembling the tender hues of the tropical sky, or the fleeting tints of the aurora borealis, were produced, and have become familiar to us in the well-known Geissler tubes.

Crookes, the celebrated English chemist, went still further, and by exhausting the bulbs with an improved Sprengel air-pump, obtained an extremely high vacuum, which gave remarkable effects (page 120). The diffused glow or cloudy light of the tube now shrank into a single stream, which joined the sparking points inserted through the ends of the tube as with a luminous thread A magnet held near the tube bent the streamer from its course; and there was a dark space or gap in it near the negative point or cathode, from which proceeded invisible rays, having the property of impressing a photographic plate, and of rendering matter in general on which they impinged phosphorescent, and, in course of time, red-hot. Where they strike on the glass of the tube it is seen to glow with a green or bluish phosphorescence, and it will ultimately soften with heat.

These are the famous "cathode rays" of which we have recently heard so much. Apparently they cannot be produced except in a very high vacuum, where the pressure of the air is about 1-100th millionth of an atmosphere, or that which it is some 90 or 100 miles above the earth. Mr Crookes regards them as a stream of airy particles electrified by contact with the cathode or negative discharging point, and repelled from it in straight lines. The rarity of the air in the tube enables these particles to keep their line without being jostled by the other particles of air in the tube. A molecular bombardment from the cathode is, in his opinion, going on, and when the shots, that is to say, the molecules of air, strike the wall of the tube, or any other body within the tube, the shock gives rise to phosphorescence or fluorescence and to heat. This, in brief, is the celebrated hypothesis of "radiant matter," which has been supported in the United Kingdom by champions such as Lord Kelvin, Sir Gabriel Stokes, and Professor Fitzgerald, but questioned abroad by Goldstem, Jaumann, Wiedemann, Ebert, and others.

Lenard, a young Hungarian, pupil of the illustrious Heinrich Hertz, was the first to inflict a serious blow on the hypothesis, by showing that the cathode rays could exist outside the tube in air at ordinary pressure. Hertz had found that a thin foil of aluminium was penetrated by the rays, and Lenard made a tube having a "window" of aluminium, through which the rays darted into the open air. Their path could be traced by the bluish phosphorescence which they excited in the air, and he succeeded in getting them to penetrate a thin metal box and take a photograph inside it. But if the rays are a stream of radiant matter which can only exist in a high vacuum, how can they survive in air at ordinary pressure? Lenard's experiments certainly favour the hypothesis of their being waves in the luminiferous ether.

Professor Rontgen, of Wirzburg, profiting by Lenard's results, accidentally discovered that the rays coming from a Crookes tube, through the glass itself, could photograph the bones in the living hand, coins inside a purse, and other objects covered up or hid in the dark. Some bodies, such as flesh, paper, wood, ebonite, or vulcanised fibre, thin sheets of metal, and so on, are more or less transparent, and others, such as bones, carbon, quartz, thick plates of metal, are more or less opaque to the rays. The human hand, for example, consisting of flesh and bones, allows the rays to pass easily through the flesh, but not through the bones. Consequently, when it is interposed between the rays and a photographic plate, the skeleton inside is photographed on the plate. A lead pencil photographed in this way shows only the black lead, and a razor with a horn handle only the blade.

Thanks to the courtesy of Mr. A. A. Campbell Swinton, of the firm of Swinton & Stanton, the well-known electrical engineers, of Victoria Street, Westminster, a skilful experimentalist, who was the first to turn to the subject in England, I have witnessed the taking of these "shadow photographs," as they are called, somewhat erroneously, for "radiographs" or "cryptographs" would be a better word, and shall briefly describe his method. Rontgen employs an induction coil insulated in oil to excite the Crookes tube and yield the rays, but Mr. Swinton uses a "high frequency current," obtained from apparatus similar to that of Tesla, and shown in figure 100, namely, a high frequency induction coil insulated by means of oil and excited by the continuous discharge of twelve half-gallon Leyden jars charged by an alternating current at a pressure of 20,000 volts produced by an ordinary large induction coil sparking across its high pressure terminals.

A vacuum bulb connected between the discharge terminals of the high frequency coil, as shown in figure 101, was illuminated with a pink glow, which streamed from the negative to the positive pole—that is to say, the cathode to the anode, and the glass became luminous with bluish phosphorescence and greenish fluorescence. Immediately under the bulb was placed my naked hand resting on a photographic slide containing a sensitive bromide plate covered with a plate of vulcanised fibre. An exposure of five or ten minutes is sufficient to give a good picture of the bones, as will be seen from the frontispiece.

The term "shadow" photograph requires a word of explanation. The bones do not appear as flat shadows, but rounded like solid bodies, as though the active rays passed through their substance. According to Rontgen, these "x" rays, as he calls them, are not true cathode rays, partly because they are not deflected by a magnet, but cathode rays transformed by the glass of the tube; and they are probably not ultra-violet rays, because they are not refracted by water or reflected from surfaces. He thinks they are the missing "longitudinal" rays of light whose existence has been conjectured by Lord Kelvin and others—that is to say, waves in which the ether sways to and fro along the direction of the ray, as in the case of sound vibrations, and not from side to side across it as in ordinary light.

Be this as it may, his discovery has opened up a new field of research and invention. It has been found that the immediate source of the rays is the fluorescence and phosphorescence of the glass, and they are more effective when the fluorescence is greenish-yellow or canary colour. Certain salts—for example, the sulphates of zinc and of calcium, barium platino-cyanide, tungstate of calcium, and the double sulphate of uranyle and potassium—are more active than glass, and even emit the rays after exposure to ordinary light, if not also in the dark. Salvioni of Perugia has invented a "cryptoscope," which enables us to see the hidden object without the aid of photography by allowing the rays to fall on a plate coated with one of these phosphorescent substances. Already the new method has been applied by doctors in examining malformations and diseases of the bones or internal organs, and in localising and extracting bullets, needles, or other foreign matters in the body. There is little doubt that it will be very useful as an adjunct to hospitals, especially in warfare, and, if the apparatus can be reduced in size, it will be employed by ordinary practitioners. It has also been used to photograph the skeleton of a mummy, and to detect true from artificial gems. However, one cannot now easily predict its future value, and applications will be found out one after another as time goes on.



CHAPTER X.

THE WIRELESS TELEGRAPH.

Magnetic waves generated in the ether (see pp. 53-95) by an electric current flowing in a conductor are not the only waves which can be set up in it by aid of electricity. A merely stationary or "static" charge of electricity on a body, say a brass ball, can also disturb the ether; and if the strength of the charge is varied, ether oscillations or waves are excited. A simple way of producing these "electric waves" in the ether is to vary the strength of charge by drawing sparks from the charged body. Of course this can be done according to the Morse code; and as the waves after travelling through the ether with the speed of light are capable of influencing conductors at a distance, it is easy to see that signals can be sent in this way. The first to do so in a practical manner was Signer Marconi, a young Italian hitherto unknown to fame. In carrying out his invention, Marconi made use of facts well known to theoretical electricians, one of whom, Dr, Oliver J. Lodge, had even sent signals with them in 1894; but it often happens in science as in literature that the recognised professors, the men who seem to have everything in their favour—knowledge, even talent—the men whom most people would expect to give us an original discovery or invention, are beaten by an outsider whom nobody heard of, who had neither learning, leisure, nor apparatus, but what he could pick up for himself.

Marconi produces his waves in the ether by electric sparks passing between four brass balls, a device of Professor Righi, following the classical experiments of Heinrich Hertz. The balls are electrified by connecting them to the well-known instrument called an induction coil, sometimes used by physicians to administer gentle shocks to invalids; and as the working of the coil is started and stopped by an ordinary telegraph key for interrupting the electric current, the sparking can be controlled according to the Morse code. In our diagram, which explains the apparatus, the four balls are seen at D, the inner and larger pair being partly immersed in vaseline oil, the outer and smaller pair being connected to the secondary or induced circuit of the induction coil C, which is represented by a wavy line. The primary or inducing circuit of the coil is connected to a battery B through a telegraph signalling key K, so that when this key is opened and closed by the telegraphist according to the Morse code, the induction coil is excited for a longer or shorter time by the current from the battery, in agreement with the longer and shorter signals of the message. At the same time longer or shorter series of sparks corresponding to these signals pass across the gaps between the four balls, and give rise to longer or shorter series of etheric waves represented by the dotted line. So much for the "Transmitter." But how does Marconi transform these invisible waves into visible or audible signals at the distant place? He does this by virtue of a property discovered by Mr. S. A. Varley as far back as 1866, and investigated by Mr. E. Branly in 1889. They found that powder of metals, carbon, and other conductors, while offering a great resistance to the passage of an electric current when in a loose state, coheres together when electric waves act upon it, and opposes much less resistance to the electric current. It follows that if a Morse telegraph instrument at the distant place be connected in circuit with a battery and some loose metal dust, it can be adjusted to work when the etheric waves pass through the dust, and only then. In the diagram R is this Morse "Receiver" joined in circuit with a battery B1; and a thin layer of nickel and silver dust, mixed with a trace of mercury, is placed between two cylindrical knobs or "electrodes" of silver fused into the glass tube d, which is exhausted of air like an electric glow lamp. Now, when the etheric waves proceeding from the transmitting station traverse the glass of the tube and act upon the metal dust, the current of the battery B1 works the Morse receiver, and marks the signals in ink on a strip of travelling paper. Inasmuch as the dust tends to stick together after a wave passes through it, however, it requires to be shaken loose after each signal, and this is done by a small round hammer head seen on the right, which gives a slight tap to the tube. The hammer is worked by a small electromagnet E, connected to the Morse instrument, and another battery b in what is called a "relay" circuit; so that after the Morse instrument marks a signal, the hammer makes a tap on the tube. As this tap has a bell-like sound, the telegraphist can also read the signals of the message by his ear.

Two "self-induction bobbins," L Ll, a well-known device of electricians for opposing resistance to electric waves, are included in the circuit of the Morse instrument the better to confine the action of the waves to the powder in the tube. Further, the tube d is connected to two metal conductors V Vl, which may be compared to resonators in music. They can be adjusted or attuned to the electric waves as a string or pipe is to sonorous waves. In this way the receiver can be made to work only when electric waves of a certain rate are passing through the tube, just as a tuning-fork resounds to a certain note; it being understood that the length of the waves can be regulated by adjusting the balls of the transmitter. As the etheric waves produced by the sparks, like ripples of water caused by dropping a stone into a pool, travel in all directions from the balls, a single transmitter can work a number of receivers at different stations, provided these are "tuned" by adjusting the conductors V Vl to the length of the waves.

This indeed was the condition of affairs at the time when the young Italian transmitted messages from France to England in March, 1899, and it is a method that since has been found useful over limited distances. But to the inventor there seemed no reason why wireless telegraphy should be limited by any such distances. Accordingly he immediately developed his method and his apparatus, having in mind the transmission of signals over considerable intervals. The first question that arose was the effect of the curvature of the Earth and whether the waves follow the surface of the Earth or were propagated in straight lines, which would require the erection of aerial towers and wires of considerable height. Then there was the question of the amount of power involved and whether generators or other devices could be used to furnish waves of sufficient intensity to traverse considerable distances.

Little by little progress was made and in January, 1901, wireless communication was established between the Isle of Wight and Lizard in Cornwall, a distance of 186 miles with towers less than 300 feet in height, so that it was demonstrated that the curvature of the Earth did not seriously affect the transmission of the waves, as towers at least a mile high would have been required in case the waves were so cut off. This was a source of considerable encouragement to Marconi, and his apparatus was further improved so that the resonance of the circuit and the variation of the capacity of the primary circuit of the oscillation transformer made for increased efficiency. The coherer was still retained and by the end of 1900 enough had been accomplished to warrant Marconi in arranging for trans-Atlantic experiments between Poldhu, Cornwall and the United States, stations being located on Cape Cod and in Newfoundland. The trans-Atlantic transmission of signals was quite a different matter from working over 100 miles or so in Great Britain. The single aerial wire was supplanted by a set of fifty almost vertical wires, supported at the top by a horizontal wire stretched between two masts 157 1/2 feet high and 52 1/2 feet apart, converging together at the lower end in the shape of a large fan. The capacity of the condenser was increased and instead of the battery a small generator was employed so that a spark 1 1/2 inches in length would be discharged between spheres 3 inches in diameter. At the end of the year 1901 temporary stations at Newfoundland were established and experiments were carried on with aerial wires raised in the air by means of kites. It was here realized that various refinements in the receiving apparatus were necessary, and instead of the coherer a telephone was inserted in the secondary circuit of the oscillation transformer, and with this device on February 12th the first signals to be transmitted across the Atlantic were heard. These early experiments were seriously affected by the fact that the antennae or aerial wires were constantly varying in height with the movement of the kites, and it was found that a permanent arrangement of receiving wires, independent of kites or balloons, was essential. Yet it was demonstrated at this time that the transmission of electric waves and their detection over distances of 2000 miles was distinctly possible.

A more systematic and thorough test occurred in February, 1902, when a receiving station was installed on the steamship Philadelphia, proceeding from Southampton to New York. The receiving aerial was rigged to the mainmast, the top of which was 197 feet above the level of the sea, and a syntonic receiver was employed, enabling the signals to be recorded on the tape of an ordinary Morse recorder. On this voyage readable messages were received from Poldhu up to a distance of 1551 miles, and test letters were received as far as 2099 miles. It was on this voyage that Marconi made the interesting discovery of the effect of sunlight on the propagation of electric waves over great distances. He found that the waves were absorbed during the daytime much more than at night and he eventually reached the conclusion that the ultraviolet light from the sun ionized the gaseous molecules of the air, and ionized air absorbs the energy of the electric waves, so that the fact was established that clear sunlight and blue skies, though transparent to light, serve as a fog to the powerful Hertzian waves of wireless telegraphy. For that reason the transmission of messages is carried on with greater facility on the shores of England and Newfoundland across the North Atlantic than in the clearer atmosphere of lower latitudes. But atmospheric conditions do not affect all forms of waves the same, and long waves with small amplitudes are far less subject to the effect of daylight than those of large amplitude and short wave length, and generators and circuits were arranged to produce the former. But the difficulty did not prove insuperable, as Marconi found that increasing the energy of the transmitting station during the daytime would more than make up for the loss of range.

The experiments begun at Newfoundland were transferred to Nova Scotia, and at Glace Bay in 1902 was established a station from which messages were transmitted and experimental work carried on until its work was temporarily interrupted by fire in 1909. Here four wooden lattice towers, each 210 feet in height, were built at the corner of a square 200 feet on a side, and a conical arrangement of 400 copper wires supported on stays between the tops of the towers and connected in the middle at the generating station was built. Additional machinery was installed and at the same time a station at Cape Cod for commercial work was built. In December, 1902, regular communication was established between Glace Bay and Poldhu, but it was only satisfactory from Canada to England as the apparatus at the Poldhu station was less powerful and efficient than that installed in Canada. The transmission of a message from President Roosevelt to King Edward marked the practical beginning of trans-Atlantic wireless telegraphy. By this time a new device for the detection of messages was employed, as the coherer we have described even in its improved forms was found to possess its limitations of sensitiveness and did not respond satisfactorily to long distance signals. A magnetic detector was devised by Marconi while other inventors had contrived electrolytic, mercurial, thermal, and other forms of detector, used for the most part with a telephone receiver in order to detect minute variations in the current caused by the reception of the electro-magnetic waves. With one of Marconi's magnetic detectors signals from Cape Cod were read at Poldhu.

In 1903 wireless telegraphy had reached such a development that the transmission of news messages was attempted in March and April of that year. But the service was suspended, owing to defects which manifested themselves in the apparatus, and in the meantime a new station in Ireland was erected. But there was no cessation of the practical experiments carried on, and in 1903 the Cunard steamship Lucania received, during her entire voyage across from New York to Liverpool, news transmitted direct from shore to shore. In the meantime intercommunication between ships had been developed and the use of wireless in naval operations was recognized as a necessity.

Various improvements from time to time were made in the aerial wires, and in 1905 a number of horizontal wires were connected to an aerial of the inverted cone type previously used. The directional aerial with the horizontal wires was tried at Glace Bay, and adopted for all the long distance stations, affording considerable strengthening of the received signals at Poldhu stations. Likewise improvements in the apparatus were effected at both trans-Atlantic stations, consisting of the adoption of air condensers composed of insulated metallic plate suspended in the air, which were found much better than the condensers where glass was previously used to separate the plates. For producing the energy employed for transmitting the signals a high tension continuous current dynamo is used. An oscillatory current of high potential is produced in a circuit which consists of rapidly rotating disks in connection with the dynamo and suitable condensers.

The production of electric oscillations can be accomplished in several ways and waves of the desired frequency and amplitude produced. Thus in 1903 it was found by Poulsen, elaborating on a principle first discovered by Duddell, that an oscillatory current may be derived from an electric arc maintained under certain conditions and that undamped high frequency waves so produced were suitable for wireless telegraphy. This discovery was of importance, as it was found that the waves so generated were undamped, that is, capable of proceeding to their destination without loss of amplitude. On this account they were especially suitable for wireless telephony where they were early applied, as it was found possible so to arrange a circuit with an ordinary microphone transmitter that the amplitude of the waves would be varied in harmony with the vibrations of the human voice. These waves so modulated could be received by some form of sensitive wave detector at a distant station and reproduced in the form of sound with an ordinary telephone receiver. With undamped waves from the arc and from special forms of generators wireless telephony over distances as great as 200 miles has been accomplished and over shorter distances, especially at sea and for sea to shore, communication has found considerable application. It is, however, an art that is just at the beginning of its usefulness, standing in much the same relation to wireless telegraphy that the ordinary telephone does to the familiar system employing metallic conductors.

On the spark and arc systems various methods of wireless telegraphy have been developed and improved so that Marconi no longer has any monopoly of methods or instruments. Various companies and government officials have devised or modified systems so that to-day wireless is practically universal and is governed by an international convention to which leading nations of the world subscribe.

One of the recent features of wireless telegraphy of interest is the success of various directional devices. As we have seen, various schemes were tried by Marconi ranging from metallic reflectors used by Hertz in his early experiments with the electric waves to the more successful arrangement of aerial conductors. In Europe Bellini and Tosi have developed a method for obtaining directed aerial waves which promises to be of considerable utility, enabling them to be projected in a single direction just as a searchlight beam and thus restrict the number of points at which the signals could be intercepted and read. Likewise an arrangement was perfected which enabled a station to determine the direction in which the waves were being projected and consequently the bearing of another vessel or lighthouse or other station. The fundamental principle was the arrangement of the antennae, two triangular systems being provided on the same mast, but in one the current is brought down in a perpendicular direction. The action depends upon the difference of the current in the two triangles.

Wireless telegraph apparatus is found installed in almost every seagoing passenger vessel of large size engaged in regular traffic, and as a means of safety as well as a convenience its usefulness has been demonstrated. Thus on the North Atlantic the largest liners are never out of touch with land on one side of the ocean or the other, and news is supplied for daily papers which are published on shipboard. Every ship in this part of the ocean equipped with the Marconi system, for example, is in communication on an average with four vessels supplied with instruments of the same system every twenty-four hours. In case of danger or disaster signals going out over the sea speedily can bring succour, as clearly was demonstrated in the case of the collision between the White Star steamship Republic and the steamship Florida on January 26, 1909. Here wireless danger messages were sent out as long as the Republic was afloat and its wireless apparatus working. These brought aid from various steamers in the vicinity and the passengers were speedily transferred from the sinking Republic. On April 15, 1912, the White Star liner Titanic, the largest ship afloat, sank off Newfoundland, after colliding with an iceberg. Wireless SOS calls for help brought several steamships to the scene, and 703 persons from a total of 2,206, were rescued. On October 9, 1913, the Uranium liner Volturno caught fire in mid- ocean, and her wireless calls brought ten steamships to her aid, which, despite a heavy sea, rescued 532 persons from a total of 657. Again, on November 14, 1913, the Spanish steamship Balmes caught fire off Bermuda, and at her wireless call the Cunard liner Pannonia saved all of her passengers—103. The Titanic horror led the principal maritime nations to take immediate steps to perfect their wireless systems, and the installation of apparatus and operators soon became a prime requisite of the equipment of the world's shipping. Wireless telegraphy has been developed to great efficiency in all the leading navies, and powerful plants are installed on all warships. The United States, Great Britain, and Germany, most noticeably, have established shore stations, by which they can "talk all around the world" from any ship or station. In operation secrecy is most important. For in the navy practically all important messages are sent in code or cipher under all conditions while in commercial work the tapping of land wires or the stealing of messages while illegal is physically possible for the evil disposed yet has never proved in practice a serious evil. The problem of interference, however, seems to have been fairly solved by the large systems though the activity of amateurs is often a serious disturbance for government and other stations.

Despite the progress of wireless telegraphy it has not yet supplanted the submarine cable and the land wire, and in conservative opinion it will be many years before it will do so. In fact, since Marconi's work there has been no diminution in the number or amount of cables laid and the business handled, nor is there prospect of such for years to come. While the cable has answered admirably for telegraphic purposes yet for telephony over considerable distances it has failed entirely so that wireless telephony over oceans starts with a more than favorable outlook. But wireless telegraphy to a large extent has made its own field and here its work has been greatly successful. Thus when Peary's message announcing his discovery of the North Pole came out of the Frozen North, it was by way of the wireless station on the distant Labrador coast that it reached an anxious and interested civilization. It is this same wireless that watches the progress of the fishing fleets at stations where commercial considerations would render impossible the maintenance of a submarine cable. It is the wireless telegraph that maintains communication in the interior of Alaska and between islands in the Pacific and elsewhere where conditions of development do not permit of the more expensive installation of submarine cable or climatic or other conditions render impossible overland lines. At sea its advantages are obvious. Everywhere the ether responds to the impulses of the crackling sparks, and even from the airship we soon may expect wireless messages as the few untrodden regions of our globe are explored.



CHAPTER XL

ELECTRO-CHEMISTRY AND ELECTRO-METALLURGY.

In no department of the application of electricity to practical work has there been a greater development than in electro- metallurgy and electro-chemistry. To-day there are vast industries depending upon electrical processes and the developments of a quarter of a century have been truly remarkable. Already more than one-half of the copper used in the arts is derived by electrolytic refining. The production of aluminum depends entirely on electricity, the electric furnace as a possible rival to the blast furnace for the production of iron and steel is being seriously considered, and many other metallurgical processes are being undertaken on a large scale. We have seen in our chapter on Electrolysis how a metal may be deposited from a solution of its salt and how this process could be used for deriving a pure metal or for plating or coating with the desired metal the surface of another metal or one covered with graphite. In the following pages it is intended to take up some of the more notable accomplishments in this field achieved by electricity, which have been developed to a state of commercial importance.

The electric arc not only supplies light, but heat of great intensity which the electrical engineer as well as the pure scientist has found so valuable for many practical operations. It is of course obvious that for most chemical operations, and especially in the field of metallurgy, heat is required for the separation of combinations of various elements, for their purification, as well as for the combination with other elements into alloys or compounds of direct utility. The usual method of generating heat is by the combustion of some fuel, such as coal, coke, gas or oil, and this has been utilized for hundreds of years in smelting metals and ores and in refining the material from a crude state. Now it may happen that a nation or region may be rich in metalliferous ores, but possess few, if any, coal deposits. Accordingly the ore must be mined and transported considerable distances for treatment and the advantages of manufacturing industries are lost to the neighborhood of its original production. But if water power is available, as it is in many mountainous countries where various ores are found, then this power can be transformed into electricity which is available as power not only in various manufacturing operations, but for primary metallurgical work in smelting the ores and obtaining the metal therefrom. A striking instance of this is the kingdom of Sweden, which contains but little coal, yet is rich in minerals and in water power, so that its waterfalls have been picturesquely alluded to as the country's "white coal." Likewise, at Niagara Falls a portion of the vast water power developed there has been used in the manufacture of aluminum, calcium carbide, carborundum, and other materials, while at other points in the United States and Canada, not to mention Europe, large industries where electricity is used for metallurgical or chemical work are carried on and the erection of new plants is contemplated.

The application of electricity to metallurgical and chemical work has been, in nearly all cases, the result of scientific research, and elaborate experimental laboratories are maintained by the various corporations interested in the present or future use of electrical processes. It is recognized by many of the older workers in this field that electrical developments are bound to come in the near future, and while they have not installed such appliances in their works yet they are keeping close watch of present developments, and in many cases experimental investigation and research is being carried on where electrical methods have not yet been introduced generally into the plant.

Prior to 1886 the refining of copper was the only electro- metallurgical industry and at that time it was carried on on a very limited scale. To-day the production of electrolytic copper as an industry is second in importance only to the actual production of that metal. From the small refinery started by James Elkington at Pembury in South Wales, a vast industry has developed in which there has been a change in the size of operations and in the details of methods rather than in the fundamental process. For a solution of copper sulphate is employed as the electrolyte, blocks of raw copper as the anodes, and thin sheets of pure copper as the cathodes. The passage of the electric current, as we have seen on page 79, in the chapter on Electrolysis, is able to decompose the copper in the electrolyte and to precipitate chemically pure copper on the cathode, the copper of the solution being replenished from the raw material used as the anode by which the current is passed into the bath. At this Welsh factory 250 tons yearly were produced, and small earthenware pots sufficed for the electrolyte. Thirty years later one American factory alone was able to produce at least 350 tons of electrolytic copper in twenty-four hours, and over 400,000 tons is the aggregate output of the refineries of the world, which is about 53 per cent, of the total raw copper production. Of this amount 85 per cent, comes from American refineries, whose output has more than doubled since 1900.

The chief reason for this increased output of electrolytic copper has been the great demand for its use in the electrical industries where not only a vast amount is consumed, but where copper of high purity, to give the maximum conductivity required by the electrical engineer, is demanded. When it is realized that every dynamo is wound with copper wire and that the same material is used for the trolley wire and for the distribution wires in electric lighting, it will be apparent how the demand for copper has increased in the last quarter of a century. Electrolytic methods not only supply a purer article and are economical to operate, especially if there is water power in the vicinity, but the copper ores contain varying amounts of silver and gold which can be recovered from the slimes obtained in the electrolytic process. Wherever possible machinery has been substituted for hand labor, the raw copper anodes have been cast, and the charging and discharging of the vats is carried on by the most modern mechanical methods in which efficiency and economy are secured. On the chemical side of the process attempts have been made to improve the electrolyte, notably by the addition of a small amount of hydrochloric acid to prevent the loss of silver in the slimes, and this part of the work is watched with quite as much care as the other stages. Electric furnaces have also been constructed for smelting copper ores, but these have not found wide application, and the problem is one of the future. For the most part the copper electrically refined is produced in an ordinary smelter. The mints of the United States are now all equipped with electrolytic refining plants to produce the pure metal needed for coinage and they have proved most satisfactory and economical.

As the electrolytic production of copper is an industry of great present importance, so the production of iron and steel by electricity promises to be of the greatest future importance. Electric furnaces for making steel are now maintained, and the industry has passed beyond an experimental condition. But it has not reached the point where it is competing with the Bessemer or the open hearth process of the manufacture of steel, while for the smelting of iron ores the electric furnace has not yet been found practical from an economic standpoint. Before 1880 Sir William Siemens showed that an electric arc could be used to melt iron or steel in a crucible, and he patented an electric crucible furnace which was the first attempt to use electricity in iron and steel manufacture. He stated that the process would not be too costly and that it had a great future before it. This was an application of the intense heat of the arc, which supplies a higher temperature than any source known except that of the sun. This heat is used to melt the metal, in which condition various impurities can be removed and necessary ingredients added. Siemens' furnace did not find extensive application, largely on account of the great metallurgical developments then taking place in the iron industry and the thorough knowledge of metallurgical processes as carried on, possessed by metallurgical engineers. But the idea by no means languished, and in 1899 Paul Heroult and other electro-metallurgists were active in developing a practical electric furnace for iron and steel work. The Swedish engineer, F. A. Kjellin, was also active and as the result of the efforts of these and other workers, by 1909 electric furnaces were employed, not only in the manufacture of special steels whose composition and making were attended with special care, but for rails and structural material. There were reported to be between thirty and forty electric steel plants in various countries, and the outlook for the future was distinctly bright. The application of electro- metallurgy at this time was confined to the manufacture of steel, as the smelting of iron had not emerged from the experimental stage of its development, though extensive trials on a large scale of various furnaces have been undertaken in Europe and by the Canadian government at Sault Ste. Marie, where the Heroult furnace, soon to be described, was employed. Electro-metallurgy of steel, as in all utilization of electrical power, depends upon obtaining electricity at a reasonable cost, and then utilizing the heat of the arc or of the current in the most practical and economical form. One of the pioneer furnaces for this purpose which has seen considerable development and practical application is the Heroult furnace, which is a tilting furnace of the crucible type, whose operation depends upon both the heat of the arc and on the heat produced by the resistance of the molten material. In the Heroult process the impurities of the molten iron are washed out by treatment with suitable slags. The furnace consists of a crucible in the form of a closed shallow iron tank, thickly lined with dolomite and magnazite brick, with a hearth of crushed dolomite. The electric current enters the crucible through two massive electrodes of solid carbon, 70 inches in length and 14 inches in diameter, so mounted that they can be moved either vertically or horizontally by the electrician in charge. These electrodes are water-jacketed to reduce the rate of consumption. The furnace contains an inlet for an air blast and openings in its covering for charging the material and for the escape of the gases. The actual process of steel-making consists of charging the crucible with steel scrap, pig iron, iron ore, and lime of the proper quality and in the right proportions, placing this material on the hearth of the furnace. Combined arc and resistance heating is applied to raise the charge to the melting point. The current is of 120 volts or the same as that used in an ordinary incandescent lighting circuit, but is alternating and of 4,000 amperes. This is for a three-ton furnace. As the material melts the lime and silicates form a slag which fuses rapidly and covers the iron and steel in the crucible, so that the molten bath is protected from the action of the gases which are liberated and the oxygen in the atmosphere. The next step in the process is to lower the electrodes until they just touch beneath the surface of the molten slag so that subsequent heating is due not to the effect of the arc but to the resistance which the bath offers to the passage of the current.

Air from an air blast is introduced into the crucible to oxidize the impurities of the metal, particularly the sulphur and the phosphorus which are carried into the slag and this is removed by the tilting of the furnace. Fresh quantities of lime, etc., are added, and the operation is repeated until a comparatively pure metal remains, when an alloy high in carbon is added and whatever other constituents are desired for the finished steel. The charge is then tipped into the casting ladle and the part of the electric furnace is finished. For three tons of steel eight to ten hours are required in the Heroult crucible furnace.

Furnaces of an altogether different type are those employing an alternating current, such as the Kjellin and Rochling furnaces, where the metal to be heated really forms the secondary circuit of a large and novel form of transformer which in principle is analogous to the familiar transformer seen to step down the potential of alternating current as for house lighting. For such a transformer the primary coil is formed of heavy wire and the secondary circuit is the molten metal which is contained in an annular channel. The current obtained in the metal is of considerable intensity, but at lower potential than that in the primary coil, and roughly is equal to that of the primary multiplied by the number of turns in the coil. The condition is similar to that in the ordinary induction coil where the current from a battery at low potential flows around a coil of a few turns and is surrounded by a second coil with a large number of turns of fine wire in which current of small intensity but of high potential is generated. In the induction furnace the reverse takes place and the current flowing in the metal derived from that of the heavy coil in the primary is of great intensity. For this type of furnace molten metal is required and the furnace is never entirely emptied, so that its process is continuous. The temperature attained is not as high as in the arc furnace, so that the raw materials used have to be of a high degree of purity, and this has proved a restriction of the field of usefulness of this type of furnace in many cases. It, however, has been improved recently and two rings of molten metal employed instead of one so that a wide centre trough is obtained in which the metal is subjected to ordinary resistance heat by direct or alternating currents. This furnace permits of various metallurgical operations and the elimination of impurities as in the Heroult type.

A third type of furnace that is meeting with some extensive use is the Giroud, which, like the Heroult furnace, is based on the arc and resistance in principle, but in its construction has a number of different features. As the current passes horizontally from the upper electrodes through the slag and molten metal in the furnace chamber to the base electrodes of the furnace, it permits of the easy regulation of the arcs and the use of lower electromotive force, while there is only one arc in the path of the current instead of two as in the Heroult type.

Sufficient quantities of steel have been made in electric furnaces to permit of the determination of the quality of the product as well as the economy of the process. It has been found in Germany that rail steel made in the induction furnace has a much higher bending and breaking limit than ordinary Bessemer or Thomas rail steel, and in Germany in 1908 rails so made commanded a considerably higher price per ton than those of ordinary rail steel. After trial orders had proved satisfactory, in 1908 5,000 tons of rails were ordered for the Italian and Swiss governments at a German works, where furnaces of eight tons capacity had been installed. In the United States only a few electric steel furnaces are in operation, and these, for the most part, for purposes of demonstration and experiment. But in Europe the industry is well established, and while at present small, is constantly growing and possesses an assured future.

In addition to the manufacture of steel, the application of the electric furnace for producing what are known as ferro-alloys, or alloys of iron, silicon, chromium, manganese, tungsten and vanadium, is now a large and important industry. Special steels have their uses in different mechanical applications and the advantage of alloying them with the rarer metals has been demonstrated for several important purposes, as for example, the use of chrome steel for armor plate, and steel containing vanadium for parts of motor cars. These industries for the most part contain electric arc furnaces and have, as their object, the manufacture of ferro-alloys, which are introduced into the steel, it having been found advantageous to use the rare metals in this form rather than in their crude state.

There is one electro-metallurgical process that has made possible the production in commercial form and for ordinary use of a metal that once was little more than a chemical curiosity. In 1885 there were produced 3.12 tons of aluminum, and its value was roughly estimated at about $12 a pound. By 1908 America alone produced over 9,000 tons valued at over $500,000,000, while European manufacturers were also large producers. In 1888 the electrolytic manufacture of aluminum was commenced in America and in the following year it was begun in Switzerland. Aluminum is formed by the electrolysis of the aluminum oxide in a fused bath of cryolite and fluorspar. The aluminum may be obtained in the form of bauxite, and is produced in large rectangular iron pots with a thick carbon lining. The pot itself is the cathode, while large graphite rods suspended in the bath serve as the anodes. After the arc is formed and the heat of the bath rises to a sufficient degree the material is decomposed and the metal is separated out so that it can be removed by ladling or with a siphon. The application of heat to obtain this metal previous to the invention of the electric furnace could only be considered a laboratory problem and the expense involved did not permit of commercial application. Now, however, aluminum is universally available and with the expiration of certain patents, the material has sold as low as 25 cents a pound.

Electrolytic methods serve also for the refining of nickel and for the production of lead, and as in other fields of metallurgy, these processes are attracting the attention of chemists and of engineers. While tin as yet has not yielded to electrolytic or electro-thermal methods with any success, the removal of tin from tin scraps and cuttings has been carried on with considerable success. With zinc the electrolytic and electro-thermal processes have not been able yet to compete with the older metallurgical method of distillation, but an important industry is electro- galvanizing, where a solution of zinc sulphate is deposited on iron and gives a protective coating. Experimental methods with the use of electricity in extracting zinc from its ores are being tested at various European plants, but the matter has not yet reached a commercial scale.

One of the earliest notable uses of the electric furnace in a large electro-chemical industry was for the production of carborundum, a carbide of silicon, which is remarkably useful as an abrasive, being available in the manufacture of grinding stones and other like purposes to replace emery and corundum. It is produced by the use of a simple electric furnace of the resistance type, where coke, sand, and sawdust are heated to a temperature of between 2000 degrees and 3000 degrees C. The chemical reaction involves the production of carbon monoxide, and gives a carbide of silicon, a crystalline solid which has the excellent abrasive properties mentioned. The manufacture was first started by its inventor, E. G. Acheson, about 1891 on a small scale, and in the following year 1,000 pounds of the material were produced at the Niagara Falls works. Within fifteen years its output had increased to well over six million pounds.

The electric furnaces at Niagara Falls have supplied many interesting electro-chemical processes. After making a carbide in the electric furnace it was found possible to decompose it by further increasing the heat to a point where the second element is volatilized and the pure carbon in the form of artificial graphite remains. In more recent work the carbide containing the silicon has been done away with and ordinary anthracite coal used as a charge from which the pure graphite is obtained. This graphite has been found especially useful in electrical work as for electrodes, while a more recent process enables a soft variety of graphite to be obtained which becomes a competitor of the natural material.

One of the most interesting of the many electro-chemical processes is the heating of lime and coke in the electric furnace so as to obtain a product in the form of calcium carbide, which, on solution in water, forms acetylene gas, a useful and valuable illuminant. This process dates from 1893 when T. L. Willson in the United States first started its manufacture on a large scale, and the great electrochemist, Henri Moissin, about the same time independently invented a similar process as a result of his notable work with the electric furnace. The process involves merely a transformation at a high temperature, a portion of the carbon in the form of coke, uniting with pulverized lime to give the calcium carbide or CaC2. Now this material, when water is added to it, decomposes, and acetylene or C2H2 is formed, which is a gas of high illuminating value as the carbon separates and glows brightly after being heated to incandescence in the flame.

The electric furnace at Niagara Falls has been able to produce still another combination in the form of siloxicon by heating carbon and silicon to a temperature slightly below that required to produce carborundum. This product is a highly refractory material and is valuable for the manufacture of crucibles, muffles, bricks, etc., for work where extreme temperatures are employed. The electric furnace enables various elements to be isolated, such. as silicon, sodium, and phosphorus, and when obtained in their pure state they find wide application.

The most important electro-chemical work of the future is to devise some means of obtaining nitrogen from the air. It is stated by scientists that the nitrogen of the soil is being exhausted and that at some future time the Earth may not be able to bear crops sufficient for the sustenance of man, unless some artificial means be found to replenish the nitrogen. Unlimited supplies of nitrogen exist in the air, but to fix it with other materials in such form that it will be useful as a fertilizer has been one of the problems to which the electro-chemists have recently devoted much attention. By the use of the electric arc and passing air through a furnace, various substances have been tried to take up the nitrogen of the air. Thus when calcium carbide is heated and brought into contact with nitrogen one atom of carbon is given up and two atoms of nitrogen take its place, resulting in the production of cyanamide.

Other important electro-chemical processes are involved in the electrolysis of the various alkaline salts to obtain metallic sodium and such products as chlorates. Thus by the electrolysis of sodium chloride metallic sodium and chlorine is obtained. From the metallic sodium solid caustic soda is then derived by a secondary reaction, while the chlorine is combined with lime to form chloride of lime or bleaching powder. In some processes the electrolysis affords directly an alkaline hypochlorite or a chlorate, the former being of wide commercial use as a bleaching agent in textile works and in the paper industry. The same process employed in the electrolysis of sodium salts is used in the case of magnesium and calcium.

Electrolysis is also made use of in the manufacture of chloroform and iodoform, as the chlorine or iodine which is produced in the electrolytic cell is allowed to act upon the alcohol or acetone under such conditions that chloroform or iodoform is produced.

Electro-chemistry plays an important part in many other industries whose omission from our description must not be considered as indicating any lack of their importance. New processes constantly are being discovered which may range all the way from the production of artificial gems to the wholesale production of the most common chemicals used in the arts. In many branches of chemical industry manufacturing processes have been completely changed, and from the research laboratories, which all large progressive manufacturers now maintain, as well as from workers in universities and scientific schools, new methods and discoveries are constantly forthcoming.



CHAPTER XII.

ELECTRIC RAILWAYS.

The electric railway of Dr. Werner von Siemens constructed at Berlin in 1879 was the forerunner of a number of systems which have had the effect of changing materially the problems of transportation in all parts of the world. The electric railway not only was found suitable as a substitute for the tramway with its horse-drawn car, but far more economical than the cable cars, which were installed to meet the transportation problems of large cities with heavy traffic, or, as in the case of certain cities on the Pacific slope, where heavy grades made transportation a serious problem. Furthermore, the electric railway was found serviceable for rural lines where small steam engines or "dummies" were operated with limited success, and then only under exceptional conditions. As a result, practically every country of the world where the density of population and the state of civilization has warranted, is traversed by a network of electric railways, securing the most complete intercommunication between the various localities and handling local transportation in a manner impossible for a railway line employing steam locomotives.

The great advance in electric transportation, aside from its meeting an economic need, has been due to the development of systems of generating and transmitting power economically over long distances. If water power is available, turbines and electric generators can be installed and power produced and transmitted over long distances, as, for example, from Niagara Falls to Buffalo, or even to much greater distances as in the case of power plants on the Pacific coast where mountain streams and lakes are employed for this purpose with considerable efficiency. A high tension alternating current thus can be transmitted over considerable distances and then transformed into direct current which flows along the trolley wires and is utilized in the motors. This transformation is usually accomplished by means of a rotary converter, that is, an alternating current motor which carries with it the essential elements of a direct current dynamo and receiving the alternating current of high potential turns it out in the form of direct current at a, lower and standard potential. The alternating current at high potential can be transmitted over long distances with a minimum of loss, while the direct current at lower potential is more suitable for the motor and can be used with greater advantage, yet its potential or pressure decreases rapidly over long lengths of line, so that it is more economical to use sub-stations to convert the alternating current from the power plant. It must not be inferred, however, that all electric railways employ direct current machinery. In Europe alternating current has been used with great success and also in the United States where a number of lines have been equipped with this form of power. But the greater number of installations employ the direct current at about 500-600 volts and this is now the usual practice. Whether it will continue so in the future or not is perhaps an open question.

The electric car, as we have seen, employs a motor which is geared to the axle of the driving trucks, and the current is derived from the trolley wire by the familiar pole and wheel and after flowing through the controller to the motor returns by the rail. The speed of the car is regulated by the amount of current which the motorman allows to pass through the motor and the circuits through which it flows in order to produce different effects in the magnetic attraction of the magnet and the armature. In the ordinary electric car for urban or suburban uses there has been a constant increase in the power of the motor and size of the cars, as it has been found that even large cars can be handled with the required facility necessary in crowded streets and that they are correspondingly more economical to maintain and operate.

The success of electric traction in large cities had been demonstrated but a few years when it was appreciated that the overhead wires of the trolley were unsightly and dangerous, especially in the case of fire or the breaking of the wires or supports. Accordingly a system was developed where the current was obtained from conductors laid in a conduit on insulated supports through a slot in the centre of the track between the rails. A plow suspended from the bottom of the car was in contact with the conductors which were steel rails mounted on insulated supports, and through them the current passed by suitable conductors to the controller and motors. This system found an immediate vogue in American cities, and though more costly to install than the overhead trolley, was far more satisfactory in its results and appearance. In certain cities, Washington, D. C., for example, the conduit is used in the built-up portion of the town and when the suburbs are reached the plow is removed and the motors are connected with the trolley wire by the usual pole and wheel.

Perhaps the most important feature of the electric railway in the United States has been the development and increase of its efficiency. Wherever possible traffic conditions warranted, it was comparatively easy to secure the right of way along country highways with little, if any, expense, and the construction of track and poles for such work was not a particularly heavy outlay. It was found, as we have seen, that the current could be transmitted over considerable distances so that the opportunity was afforded to supply transportation between two towns at some small distance where the local business at the time of the construction of the road would not warrant the outlay. This led to the systems of interurban lines, small at first, but as their success was demonstrated, gradually extending and uniting so that not only two important towns were connected, but eventually a large territory was supplied with adequate transportation facilities and even mail, express, and light freight could be handled.

Again the success of such enterprises made it feasible for the electric railways to forsake the public highway and to secure a right of way of their own, and gradually to develop express and through service, often in direct competition with the local service of the steam railways in the same territory. Here larger cars were required and power stations of the most modern and efficient type in order to secure proper economy of operation. The general character of machinery, both generators and motors, was preserved even for these long distance lines, and their operation became simply an engineering problem to secure the maximum efficiency with a minimum expenditure.

With the success of electric railways in cities and for suburban and interurban service naturally arose the question, why electric power whose availability and economy had been shown in so many circumstances could not be used for the great trunk lines where steam locomotives have been developed and employed for so many years? The question is not entirely one of engineering unless as part of the engineering problem we consider the various economic elements that enter into the question, and their investigation is the important task of the twentieth century engineer. For he must answer the question not only is a method possible mechanically, but is it profitable from a practical and economic standpoint? And it is here that the question of the electrification of trunk lines now rests. The steam locomotive has been developed to a point perhaps of almost maximum efficiency where the greatest speed and power have been secured that are possible on machines limited by the standard gauge of the track, 4 feet 8 1/2 inches, and the curves which present railway lines and conditions of construction demand. Now, withal, the steam locomotive mechanically considered is inefficient, as it must take with it a large weight of fuel and water which must be transformed into steam under fixed conditions. If for example, we have one train a day working over a certain line, there would be no question of the economy of a steam locomotive, but with a number, we are simply maintaining isolated units for the production of power which could be developed to far greater advantage in a central plant. Just as the factory is more economical than a number of workers engaged at their homes, and the large establishment of the trust still more economical in production than a number of factories, so the central power station producing electricity which can be transmitted along a line and used as required is obviously more advantageous than separate units producing power on the spot with various losses inherent in small machines.

But even if the central station is theoretically superior and more economical it does not imply that it is either good policy or economy to electrify at once all the trunk lines of a country such as the United States and to send to the scrap heap thousands of good locomotives at the sacrifice of millions of dollars and the outlay of millions more for electrical equipment. In other words, unless the financial returns will warrant it, there is no good and positive reason for the electrification of our great trans- continental lines and even shorter railroads. That is the situation to-day, but to-morrow is another question, and the far- seeing railroad man must be ready with his answer and with his preparations. To-day terminal services in large cities can better be performed by electricity, and not only is there economy in their operation, but the absence of dirt, smoke and noise is in accord with public sentiment if not positively demanded by statute or ordinance. Suburban service can be worked much more economically and effectively by trains of motor cars, and time table and schedule are not limited by the number of available locomotives on a line so equipped. On mountain grades, where auxiliary power or engines of extreme capacity are required, electricity generated by water power from melting snow or mountain lakes or streams in the vicinity may be availed of. Under such conditions powerful motors can be used on mountain divisions, not only with economy, but with increased comfort to passengers, especially where there are long tunnels. All this and more the railway man of to-day realizes, and electrification to this extent has been accomplished or is in course of construction. For each one of the services mentioned typical installations can be given as examples, and to accomplish the various ends, there is not only one system but several systems of electrical working, which have been devised by electrical engineers to meet the difficulties.

To summarize then, electric working of a trunk line results in increased economy over steam locomotives by concentration of the power and especially by the use of water power where possible. Thus economy is secured to the greatest extent by a complete electrical service and not by a mixed service of electric and steam locomotives. Electrification gives an increase in capacity both in the haulage by a locomotive, an electric locomotive being capable of more work than a steam locomotive, and in schedule and rate of speed, as motor car trains and electric terminal facilities make possible augmented traffic, and an increased use of dead parts of the system such as track and roadbed. There is a great gain in time of acceleration and for stopping, and for the Boston terminal it was estimated that with electricity 50 per cent, more traffic could be handled, as the headway could be reduced from three to two minutes. The modern tendency of electrification deals either with special conditions or where the traffic is comparatively dense. From such a beginning it is inevitable that electric working should be extended and that is the tendency in all modern installations, as for example, at the New York terminal of the New York Central and Hudson River Railroad where the electric zone, first installed within little more than station limits, is gradually being extended. As examples of density of traffic suitable for electrification, yet at the same time possessing problems of their own, are the great terminals such as the Grand Central Station of the New York Central and Hudson River Railroad in New York City, the new Pennsylvania Station in the same city, and that of the Illinois Central Station in the city of Chicago. Not only is there density here but the varied character of the service rendered, such as express, local, suburban, and freight, involves the prompt and efficient handling of trains and cars. Now, with suburban trains made up of motor cars, a certain number of locomotives otherwise employed are released; for these cars can be operated or shifted by their own power. Such terminal stations are often combined with tunnel sections, as in the case of the great Pennsylvania terminal, where the tunnel begins at Bergen, New Jersey, and extends under the Hudson River, beneath Manhattan Island and under the East River to Long Island City. It is here that electric working is essential for the comfort of passengers as well as for efficient operation. But there are tunnel sections not connected with such vast terminals, as in the case of the St. Clair tunnel under the Detroit River.

While the field and future direction of electrification is fairly well outlined and its future is assured, yet this future will be one of steady progress rather than one of sudden upheaval for the economic reasons before stated. To-day there are no final standards either of systems or of motors and the field is open for the final evolution of the most efficient methods. Notwithstanding the extraordinary progress that has been made many further developments are not only possible now but will be demanded with the progress of the art.

The great problem of the electric railway is the transmission of energy, and while power may be economically generated at the central station, yet, as Mr. Frank J. Sprague, one of the pioneers and foremost workers in the electrical engineering of railways has so aptly said, it is still at that central station and it will suffer a certain diminution in being carried to the point of utilization as well as in being transformed into power to move locomotives, so that these two considerations lie at the bottom of the electric railway and on them depend the choice of the system and the design and construction of the motor. The two fundamental systems for electric railways, as in other power problems, are the direct current and the alternating current. In the former we have the familiar trolley wire, fed perhaps by auxiliary conductors carried on the supporting poles or the underground trolley in the conduit, or the third rail laid at the side of the track. All of these have become standard practice and are operated at the usual voltage of from 500 to 600 volts. The current on lines of any considerable length is alternating current, supplied from large central generating stations and transformed to direct as occasion may demand at suitable sub-stations. Recently there has been a tendency to employ high voltage direct current systems where the advantages of the use of direct current motors are combined with the economies of high voltage transmission, chief of which are the avoiding of power losses in transmission and the economy in the first cost of copper. These high voltage direct current lines were first used in Europe, and during the year 1907 experimental lines on the Vienna railway were tested. IN Germany and Switzerland tests were made of direct current system of 2,000 and 3,000 volts and in 1908 there was completed the first section of a 1,200-volt direct current line between Indianapolis and Louisville, which marked the first use of high tension direct current in the United States, and this was followed by other successful installations.

With alternating current there can be used the various forms of single phase or polyphase current familiar in power work, but the latter is now preferred, and in Europe and in the United States in the latter part of 1908 the number of single phase lines was estimated at 27 and 28 respectively, with a total mileage of 782 and 967 miles. A trolley wire or suspended conductor is used. To employ a single phase current, motors of either the repulsion type or of the series type are used and are of heavier weight than the direct current motors, as they must combine the functions of a transformer and a motor. It is for this reason that we often see two electric locomotives at the head of a single train on lines where the single phase system is employed, while on neighboring lines using direct current, one locomotive of hardly larger size suffices. With the polyphase current a motor with a rotating field is used, and they have considerable efficiency as regards weight when compared with the single phase and with the direct current motor. The polyphase motor, however, is open to the objection that it does not lend itself to regulations as well as the direct current form, and with ingenious devices involving the arrangement of the magnetic field and the combination of motors, various running speeds can be had. The usual voltage for these motors is 3,000 volts, but in the polyphase plant designed for the Cascade Tunnel 6,000 volts are to be used. They possess many advantages, especially their ability to run at overload, and consequently a locomotive with polyphase motor will run up grade without serious loss of speed. The single phase system has been carried on on Swiss and Italian railroads, notably on the Simplon Tunnel and the Baltelina lines with great success, and the distribution problems are reduced to a minimum. In the United States a notable installation has been on the New York, New Haven & Hartford Railroad, where the section between Stamford and New York has been worked by electricity exclusively since July 1, 1908. Here the single phase motors use direct current while running over the tracks of the New York Central from Woodlawn to the Grand Central Terminal. On both the New York, New Haven & Hartford and the New York Central locomotives the armature is formed directly on the axle of the driving wheels, so consequently much interest attaches to the new design adopted for the Pennsylvania tunnels, where the armatures of the direct current motors are connected with the driving wheels by connecting rods somewhat after the fashion of the steam locomotive, and following in this respect some successful European practice.