In practice electricity is measured by various units or standards named after celebrated electricians. Thus the unit of quantity is the coulomb, the unit of current or quantity flowing per second is the ampere, the unit of electromotive force is the volt, and the unit of resistance is the ohm.

The quantity of water or any other "electrolyte" decomposed by electricity is proportional to the strength of the current. One ampere decomposes .00009324 gramme of water per second, liberating .000010384 gramme of hydrogen and .00008286 gramme of oxygen.

The quantity in grammes of any other chemical element or ion which is liberated from an electrolyte or body capable of electrochemical decomposition in a second by a current of one ampere is given by what is called the electrochemical equivalent of the ion. This is found by multiplying its ordinary chemical equivalent or combining weight by .000010384, which is the electrochemical equivalent of hydrogen. Thus the weight of metal deposited from a solution of any of its salts by a current of so many amperes in so many seconds is equal to the number of amperes multiplied by the number of seconds, and by the electrochemical equivalent of the metal.

The deposition of a metal from a solution of its salt is very easily shown in the case of copper. In fact, we have already seen that in the Daniell cell the current decomposes a solution of sulphate of copper and deposits the pure metal on the copper plate. If we simply make a solution of blue vitriol in a glass beaker and dip the wires from a voltaic cell into it, we shall find the wire from the negative pole become freshly coated with particles of new copper. The sulphate has been broken up, and the liberated metal, being positive, gathers on the negative electrode. Moreover, if we examine the positive electrode we shall find it slightly eaten away, because the sulphuric acid set free from the sulphate has combined with the particles of that wire to make new sulphate. Thus the copper is deposited on one electrode, namely, the cathode, by which the current leaves the bath, and at the expense of the other electrode, that is to say, the anode, by which the current enters the bath.

The fact that the weight of metal deposited in this way from its salts is proportional to the current, has been utilised for measuring the strength of currents with a fine degree of accuracy. If, for example, the tubes of the voltameter described on page 38 were graduated, the volume of gas evolved would be a measure of the current. Usually, however, it is the weight of silver or copper deposited from their salts in a certain time which gives the current in amperes.

Electro-plating is the principal application of this chemical process. In 1805 Brugnatelli took a silver medal and coated it with gold by making it the cathode in a solution of a salt of gold, and using a plate of gold for the anode. The shops of our jewellers are now bright with teapots, salt cellars, spoons, and other articles of the table made of inferior metals, but beautified and preserved from rust in this way.

Figure 44 illustrates an electro-plating bath in which a number of spoons are being plated. A portion of the vat V is cut away to show the interior, which contains a solution S of the double cyanide of gold and potassium when gold is to be laid, and the double cyanide of silver and potassium when silver is to be deposited. The electrodes are hung from metal rods, the anode A being a plate of gold or silver G, as the case may be, and the cathode C the spoons in question. When the current of the battery or dynamo passes through the bath from the anode to the cathode, gold or silver is deposited on the spoons, and the bath recuperates its strength by consuming the gold or silver plate.

Enormous quantities of copper are now deposited in a similar way, sulphate of copper being the solution and a copper plate the anode. Large articles of iron, such as the parts of ordnance, are sometimes copper-plated to preserve them from the action of the atmosphere. Seamless copper pipes for conveying steam, and wires of pure copper for conducting electricity, are also deposited, and it is not unlikely that the kettle of the future will be made by electrolysis.

Nickel-plating is another extensive branch of the industry, the white nickel forming a cloak for metals more subject to corrosion. Nickel is found to deposit best from a solution of the double sulphate of nickel and ammonia. Aluminium, however, has not yet been successfully deposited by electricity.

In 1836 De la Rue observed that copper laid in this manner on another surface took on its under side an accurate impression of that surface, even to the scratches on it, and three years later Jacobi, of St. Petersburg, and Jordan, of London, applied the method to making copies or replicas of medals and woodcuts. Even non-metallic surfaces could be reproduced in copper by taking a cast of them in wax and lining the mould with fine plumbago, which, being a conductor, served as a cathode to receive the layer of metal. It is by the process of electrotyping or galvano- plastics that the copper faces for printing woodcuts are prepared, and copies made of seals or medals.

Natural objects, such as flowers, ferns, leaves, feathers, insects, and lizards, can be prettily coated with bronze or copper, not to speak of gold and silver, by a similar process. They are too delicate to be coated with black lead in order to receive the skin of metal, but they can be dipped in solutions, leaving a film which can be reduced to gold or silver. For instance, they may be soaked in an alcoholic solution of nitrate of silver, made by shaking 2 parts of the crystals in 100 parts of alcohol in a stoppered bottle. When dry, the object should be suspended under a glass shade and exposed to a stream of sulphuretted hydrogen gas; or it may be immersed in a solution of 1 part of phosphorus in 15 parts of bisulphide of carbon, 1 part of bees-wax, 1 part of spirits of turpentine, 1 part of asphaltum, and 1/8 part of caoutchouc dissolved in bisulphide of carbon. This leaves a superficial film which is metallised by dipping in a solution of 20 grains of nitrate of silver to a pint of water. On this metallic film a thicker layer of gold and silver in different shades can be deposited by the current, and the silver surface may also be "oxidised" by washing it in a weak solution of platinum chloride.

Electrolysis is also used to some extent in reducing metals from their ores, in bleaching fibre, in manufacturing hydrogen and oxygen from water, and in the chemical treatment of sewage.



CHAPTER VI.

THE TELEGRAPH AND TELEPHONE.

Like the "philosopher's stone," the "elixir of youth," and "perpetual motion," the telegraph was long a dream of the imagination. In the sixteenth century, if not before, it was believed that two magnetic needles could be made sympathetic, so that when one was moved the other would likewise move, however far apart they were, and thus enable two distant friends to communicate their minds to one another.

The idea was prophetic, although the means of giving effect to it were mistaken. It became practicable, however, when Oersted discovered that a magnetic needle could be swung to one side or the other by an electric current passing near it.

The illustrious Laplace was the first to suggest a telegraph on this principle. A wire connecting the two poles of a battery is traversed, as we know, by an electric current, which makes the round of the circuit, and only flows when that circuit is complete. However long the wire may be, however far it may run between the poles, the current will follow all its windings, and finish its course from pole to pole of the battery. You may lead the wire across the ocean and back, or round the world if you will, and the current will travel through it.

The moment you break the wire or circuit, however, the current will stop. By its electromotive force it can overcome the resistance of the many miles of conductor; but unless it be unusually strong it cannot leap across even a minute gap of air, which is one of the best insulators.

If, then, we have a simple device easily manipulated by which we can interrupt the circuit of the battery, in accordance with a given code, we shall be able to send a series of currents through the wire and make sensible signals wherever we choose. These signs can be produced by the deviation of a magnetic needle, as Laplace pointed out, or by causing an electro-magnet to attract soft iron, or by chemical decomposition, or any other sensible effect of the current.

Ampere developed the idea of Laplace into a definite plan, and in 1830 or thereabout Ritchie, in London, and Baron Schilling, in St. Petersburg, exhibited experimental models. In 1833 and afterwards Professors Gauss and Weber installed a private telegraph between the observatory and the physical cabinet of the University of Gottingen. Moreover, in 1836 William Fothergill Cooke, a retired surgeon of the Madras army, attending lectures on anatomy at the University of Heidelberg, saw an experimental telegraph of Professor Moncke, which turned all his thoughts to the subject. On returning to London he made the acquaintance of Professor Wheatstone, of King's College, who was also experimenting in this direction, and in 1836 they took out a patent for a needle telegraph. It was tried successfully between the Euston terminus and the Camden Town station of the London and North-Western Railway on the evening of July 25th, 1837, in presence of Mr. Robert Stephenson, and other eminent engineers. Wheatstone, sitting in a small room near the booking-office at Euston, sent the first message to Cooke at Camden Town, who at once replied. "Never," said Wheatstone, "did I feel such a tumultuous sensation before, as when, all alone in the still room, I heard the needles click, and as I spelled the words I felt all the magnitude of the invention pronounced to be practicable without cavil or dispute."

The importance of the telegraph in working railways was manifest, and yet the directors of the company were so purblind as to order the removal of the apparatus, and it was not until two years later that the Great Western Railway Company adopted it on their line from Paddington to West Drayton, and subsequently to Slough. This was the first telegraph for public use, not merely in England, but the world. The charge for a message was only a shilling, nevertheless few persons availed themselves of the new invention, and it was not until its fame was spread abroad by the clever capture of a murderer named Tawell that it began to prosper. Tawell had killed a woman at Slough, and on leaving his victim took the train for Paddington. The police, apprised of the murder, telegraphed a description of him to London. The original "five needle instrument," now in the museum of the Post Office, had a dial in the shape of a diamond, on which were marked the letters of the alphabet, and each letter of a word was pointed out by the movements of a pair of needles. The dial had no letter "q," and as the man was described as a quaker the word was sent "kwaker." When the tram arrived at Paddington he was shadowed by detectives, and to his utter astonishment was quietly arrested in a tavern near Cannon Street.

In Cooke and Wheatstone's early telegraph the wire travelled the whole round of the circuit, but it was soon found that a "return" wire in the circuit was unnecessary, since the earth itself could take the place of it. One wire from the sending station to the receiving station was sufficient, provided the apparatus at each end were properly connected to the ground. This use of the earth not only saved the expense of a return wire, but diminished the resistance of the circuit, because the earth offered practically no resistance.

Figure 45 is a diagram of the connections in a simple telegraph circuit. At each of the stations there is a battery B B', an interruptor or sending key K K'to make and break the continuity of the circuit, a receiving instrument R R'to indicate the signal currents by their sensible effects, and connections with ground or "earth plates" E E' to engage the earth as a return wire. These are usually copper plates buried in the moist subsoil or the water pipes of a city. The line wire is commonly of iron supported on poles, but insulated from them by earthenware "cups" or insulators.

At the station on the left the key is in the act of SENDING a message, and at the post on the right it is conformably in the position for receiving the message. The key is so constructed that when it is at rest it puts the line in connection with the earth through the RECEIVING INSTRUMENT and the earth plate.

The key K consists essentially of a spring-lever, with two platinum contacts, so placed that when the lever is pressed down by the hand of the telegraphist it breaks contact with the receiver R, and puts the line-wire L in connection with the earth E through the battery B, as shown on the left. A current then flows into the line and traverses the receiver R' at the distant station, returning or seeming to return to the sending battery by way of the earth plate E' on the right and the intermediate ground.

The duration of the current is at the will of the operator who works the sending-key, and it is plain that signals can be made by currents of various lengths. In the "Morse code" of signals, which is now universal, only two lengths of current are employed— namely, a short, momentary pulse, produced by instant contact of the key, and a jet given by a contact about three times longer. These two signals are called "dot" and "dash," and the code is merely a suitable combination of them to signify the several letters of the alphabet. Thus e, the commonest letter in English, is telegraphed by a single "dot," and the letter t by a single "dash," while the letter a is indicated by a "dot" followed after a brief interval or "space" by a dash.

Obviously, if two kinds of current are used, that is to say, if the poles of the battery are reversed by the sending-key, and the direction of the current is consequently reversed in the circuit, there is no need to alter the length of the signal currents, because a momentary current sent in one direction will stand for a "dot" and in the other direction for a "dash." As a matter of fact, the code is used in both ways, according to the nature of the line and receiving instrument. On submarine cables and with needle and "mirror" instruments, the signals are made by reversing currents of equal duration, but on land lines worked by "Morse" instruments and "sounders," they are produced by short and long currents.

The Morse code is also used in the army for signalling by waving flags or flashing lights, and may also be serviceable in private life. Telegraph clerks have been known to "speak" with each other in company by winking the right and left eye, or tapping with their teaspoon on a cup and saucer. Any two distinct signs, however made, can be employed as a telegraph by means of the Morse code, which runs as shown in figure 46.

The receiving instruments R R' may consist of a magnetic needle pivotted on its centre and surrounded by a coil of wire, through which the current passes and deflects the needle to one side or the other, according to the direction in which it flows. Such was the pioneer instrument of Cooke and Wheatstone, which is still employed in England in a simplified form as the "single" and "double" needle-instrument on some of the local lines and in railway telegraphs. The signals are made by sending momentary currents in opposite directions by a "double current" key, which (unlike the key K in figure 45) reverses the poles

A .- J -.-. B -... K -.- C ... L — D -.. M - - E . N -. F .-. O . . G —. Q ..-. H . .. R . .. I ..

S ... 1 .—. T - 2 ..-.. U ..- 3 ...-. V ...- 4 ....- W .- 5 —- X .-.. 6 ...... Y .. .. 7 —.. Z ... . 8 -.. .. & . .. 9 -..- Period ..—.. 0 —— Comma .-.-

The International (Morse) code used elsewhere is the same as the above, with the following exceptions:

C -.-. Q —.- F . -. R .-. J .—- X -..- L .-.. Y -.— O —- Z —.. P .—.

FIG. 46.—Morse Signal Alphabet.

of the battery, in putting the line to one or the other, and thus making the "dot" signal with the positive and the "dash" signal with the negative pole. It follows that if the "dot" is indicated by a throw of the needle to the right side, a "dash" will be given by a throw to the left.

Most of the telegraph instruments for land lines are based on the principle of the electro-magnet. We have already seen (page 59) how Ampere found that a spiral of wire with a current flowing in it behaved like a magnet and was able to suck a piece of soft iron into it. If the iron is allowed to remain there as a core, the combination of coil and core becomes an electro-magnet, that is to say, a magnet which is only a magnet so long as the current passes. Figure 47 represents a simple "horse-shoe" electro-magnet as invented by Sturgeon. A U-shaped core of soft iron is wound with insulated wire W, and when a current is sent through the wire, the core is found to become magnetic with a "north" pole in one end and a "south" pole in the other. These poles are therefore able to attract a separate piece of soft iron or armature A. When the current is stopped, however, the core ceases to be a magnet and the armature drops away. In practice the electromagnet usually takes the form shown in figure 48, where the poles are two bobbins or solenoids of wire 61 having straight cores of iron which are united by an iron bar B, and A is the armature.

Such an electromagnet is a more powerful device than a swinging needle, and better able to actuate a mechanism. It became the foundation of the recording instrument of Samuel Morse, the father of the telegraph in America. The Morse, or, rather, Morse and Vail instrument, actually marks the signals in "dots" and "dashes" on a ribbon of moving paper. Figure 49 represents the Morse instrument, in which an electromagnet M attracts an iron armature A when a current passes through its bobbins, and by means of a lever L connected with the armature raises the edge of a small disc out of an ink-pot I against the surface of a travelling slip of paper P, and marks a dot or dash upon it as the case may be. The rest of the apparatus consists of details and accessories for its action and adjustment, together with the sending-key K, which is used in asking for repetitions of the words, if necessary.

A permanent record of the message is of course convenient, nevertheless the operators prefer to "read" the signals by the ear, rather than the eye, and, to the annoyance of Morse, would listen to the click of the marking disc rather than decipher the marks on the paper. Consequently Alfred Vail, the collaborator of Morse, who really invented the Morse code, produced a modification of the recording instrument working solely for the ear. The "sounder," as it is called, has largely driven the "printer" from the field. This neat little instrument is shown in figure 50, where M is the electromagnet, and A is the armature which chatters up and down between two metal stops, as the current is made and broken by the sending-key, and the operator listening to the sounds interprets the message letter by letter and word by word.

The motion of the armature in both of these instruments takes a sensible time, but Alexander Bain, of Thurso, by trade a watchmaker, and by nature a genius, invented a chemical telegraph which was capable of a prodigious activity. The instrument of Bain resembled the Morse in marking the signals on a tape of moving paper, but this was done by electrolysis or electro-chemical decomposition. The paper was soaked in a solution of iodide of potassium in starch and water, and the signal currents were passed through it by a marking stylus or pencil of iron. The electricity decomposed the solution in its passage and left a blue stain on the paper, which corresponded to the dot and dash of the Morse apparatus. The Bain telegraph can record over 1000 words a minute as against 40 to 50 by the Morse or sounder, nevertheless it has fallen into disuse, perhaps because the solution was troublesome.

It is stated that a certain blind operator could read the signals by the smell of the chemical action; and we can well believe it. In fact, the telegraph appeals to every sense, for a deaf clerk can feel the movements of a sounder, and the signals of the current can be told without any instrument by the mere taste of the wires inserted in the mouth.

A skilful telegraphist can transmit twenty-five words a minute with the single-current key, and nearly twice as many by the double-current key, and if we remember that an average English word requires fifteen separate signals, the number will seem remarkable; but by means of Wheatstone's automatic sender 150 words or more can be sent in a minute.

Among telegraphs designed to print the message in Roman type, that of Professor David Edward Hughes is doubtless the fittest, since it is now in general use on the Continent, and conveys our Continental news. In this apparatus the electromagnet, on attracting its armature, presses the paper against a revolving type wheel and receives the print of a type, so that the message can be read by a novice. To this effect the type wheel at the receiving station has to keep in perfect time as it revolves, so that the right letter shall be above the paper when the current passes. Small varieties of the type-printer are employed for the distribution of news and prices in most of the large towns, being located in hotels, restaurants, saloons, and other public places, and reporting prices of stocks and bonds, horse races, and sporting and general news. The "duplex system," whereby two messages, one in either direction, can be sent over one wire simultaneously without interfering, and the quadruplex system, whereby four messages, two in either direction, are also sent at once, have come into use where the traffic over the lines is very great. Both of these systems and their modifications depend on an ingenious arrangement of the apparatus at each end of the line, by which the signal currents sent out from one station do not influence the receivers there, but leave them free to indicate the currents from the distant station. When the Wheatstone Automatic Sender is employed with these systems about 500 words per minute can be sent through the line. Press news is generally sent by night, and it is on record, that during a great debate in Parliament, as many as half a million words poured out of the Central Telegraph Station at St. Martin's-le-Grand in a single night to all parts of the country.

Errors occur now and then through bad penmanship or the similarity of certain signals, and amusing telegrams have been sent out, as when the nomination of Mr. Brand for the Speakership of the Commons took the form of "Proposed to brand Speaker"; and an excursion party assured their friends at home of their security by the message, "Arrived all tight."

Telegraphs, in the literal sense of the word, which actually write the message as with a pen, and make a copy or facsimile of the original, have been invented from time to time. Such are the "telegraphic pen" of Mr. E. A. Cowper, and the "telautographs" of Mr. J. H. Robertson and Mr. Elisha Gray. The first two are based on a method of varying the strength of the current in accordance with the curves of the handwriting, and making the varied current actuate by means of magnetism a writing pen or stylus at the distant station. The instrument of Gray, which is the most successful, works by intermittent currents or electrical impulses, that excite electro-magnets and move the stylus at the far end of the line. They are too complicated for description here, and are not of much practical importance.

Telegraphs for transmitting sketches and drawings have also been devised by D'Ablincourt and others, but they have not come into general use. Of late another step forward has been taken by Mr. Amstutz, who has invented an apparatus for transmitting photographic pictures to a distance by means of electricity. The system may be described as a combination of the photograph and telegraph. An ordinary negative picture is taken, and then impressed on a gelatine plate sensitised with bichromate of potash. The parts of the gelatine in light become insoluble, while the parts in shade can be washed away by water. In this way a relief or engraving of the picture is obtained on the gelatine, and a cross section through the plate would, if looked at edgeways, appear serrated, or up and down, like a section of country or the trace of the stylus in the record of a phonograph. The gelatine plate thus carved by the action of light and water is wrapped round a revolving drum or barrel, and a spring stylus or point is caused to pass over it as the barrel revolves, after the manner of a phonographic cylinder. In doing so the stylus rises and falls over the projections in the plate and works a lever against a set of telegraph keys, which open electric contacts and break the connections of an electric battery which is joined between the keys and the earth. There are four keys, and when they are untouched the current splits up through four by-paths or bobbins of wire before it enters the line wire and passes to the distant station. When any of the keys are touched, however, the corresponding by-path or bobbin is cut out of circuit. The suppression of a by-path or channel for the current has the effect of adding to the "resistance" of the line, and therefore of diminishing the strength of the current. When all the keys are untouched the resistance is least and the current strongest. On the other hand, when all the keys but the last are touched, the resistance is greatest and the current weakest. By this device it is easy to see that as the stylus or tracer sinks into a hollow of the gelatine, or rises over a height, the current in the line becomes stronger or weaker. At the distant station the current passes through a solenoid or hollow coil of wire connected to the earth and magnetises it, so as to pull the soft iron plug or "core" with greater or less force into its hollow interior. The up and down movement of the plug actuates a graving stylus or point through a lever, and engraves a copy of the original gelatine trace on the surface of a wax or gelatine plate overlying another barrel or drum, which revolves at a rate corresponding to that of the barrel at the transmitting station. In this way a facsimile of the gelatine picture is produced at the distant station, and an electrotype or cliche of it can be made for printing purposes. The method is, in fact, a species of electric line graving, and Mr. Amstutz hopes to apply it to engraving on gold, silver, or any soft metal, not necessarily at a distance.

We know that an electric current in one wire can induce a transient current in a neighbouring wire, and the fact has been utilised in the United States by Phelps and others to send messages from moving trains. The signal currents are intermittent, and when they are passed through a conductor on the train they excite corresponding currents in a wire run along the track, which can be interpreted by the hum they make in a telephone. Experiments recently made by Mr. W. H. Preece for the Post Office show that with currents of sufficient strength and proper apparatus messages can be sent through the air for five miles or more by this method of induction.

We come now to the submarine telegraph, which differs in many respects from the overland telegraph. Obviously, since water and moist earth is a conductor, a wire to convey an electric current must be insulated if it is intended to lie at the bottom of the sea or buried underground. The best materials for the purpose yet discovered are gutta-percha and india-rubber, which are both flexible and very good insulators.

The first submarine cable was laid across the Channel from Dover to Calais in 1851, and consisted of a copper strand, coated with gutta-percha, and protected from injury by an outer sheath of hemp and iron wire. It is the general type of all the submarine cables which have been deposited since then in every part of the world. As a rule, the armour or sheathing is made heavier for shore water than it is for the deep sea, but the electrical portion, or "core," that is to say, the insulated conductor, is the same throughout.

The first Atlantic cable was laid in 1858 by Cyrus W. Field and a company of British capitalists, but it broke down, and it was not until 1866 that a new and successful cable was laid to replace it. Figure 51 represents various cross-sections of an Atlantic cable deposited in 1894.

The inner star of twelve copper wires is the conductor, and the black circle round it is the gutta-percha or insulator which keeps the electricity from escaping into the water. The core in shallow water is protected from the bites of teredoes by a brass tape, and the envelope or armour consists of hemp and iron wire preserved from corrosion by a covering of tape and a compound of mineral pitch and sand.

The circuit of a submarine line is essentially the same as that of a land line, except that the earth connection is usually the iron sheathing of the cable in lieu of an earth-plate. On a cable, however, at least a long cable, the instruments for sending and receiving the messages are different from those employed on a land line. A cable is virtually a Leyden jar or condenser, and the signal currents in the wire induce opposite currents in the water or earth. As these charges hold each other the signals are retarded in their progress, and altered from sharp sudden jets to lagging undulations or waves, which tend to run together or coalesce. The result is that the separate signal currents which enter a long cable issue from it at the other end in one continuous current, with pulsations at every signal, that is to say, in a lapsing stream, like a jet of water flowing from a constricted spout. The receiving instrument must be sufficiently delicate to manifest every pulsation of the current. Its indicator, in fact, must respond to every rise and fall of the current, as a float rides on the ripples of a stream.

Such an instrument is the beautiful "mirror" galvanometer of Lord Kelvin, Ex-President of the Royal Society, which we illustrate in figure 52, where C is a coil of wire with a small magnetic needle suspended in its heart, and D is a steel magnet supported over it. The needle (M figure 53) is made of watch spring cemented to the back of a tiny mirror the size of a half-dime which is hung by a single fibre of floss silk inside an air cell or chamber with a glass lens G in front, and the coil C surrounds it. A ray of light from a lamp L (figure 52) falls on the mirror, and is reflected back to a scale S, on which it makes a bright spot. Now, when the coil C is connected between the end of the cable and the earth, the signal current passing through it causes the tiny magnet to swing from side to side, and the mirror moving with it throws the beam up and down the scale. The operator sitting by watches the spot of light as it flits and flickers like a fire-fly in the darkness, and spells out the mysterious message.

A condenser joined in the circuit between the cable and the receiver, or between the receiver and the earth, has the effect of sharpening the waves of the current, and consequently of the signals. The double-current key, which reverses the poles of the battery and allows the signal currents to be of one length, that is to say, all "dots," is employed to send the message.

Another receiving instrument employed on most of the longer cables is the siphon recorder of Lord Kelvin, shown in figure 54, which marks or writes the message on a slip of travelling paper. Essentially it is the inverse of the mirror instrument, and consists of a light coil of wire S suspended in the field between the poles of a strong magnet M. The coil is attached to a fine siphon (T5) filled with ink, and sometimes kept in vibration by an induction coil so as to shake the ink in fine drops upon a slip of moving paper. The coil is connected between the cable and the earth, and, as the signal current passes through, it swings to one side or the other, pulling the siphon with it. The ink, therefore, marks a wavy line on the paper, which is in fact a delineation of the rise and fall of the signal current and a record of the message. The dots in this case are represented by the waves above, and the "dashes" by the waves below the middle line, as may be seen in the following alphabet, which is a copy of one actually written by the recorder on a long submarine cable.

Owing to induction, the speed of signalling on long cables is much slower than on land lines of the same length, and only reaches from 25 to 45 words a minute on the Atlantic cables, or 30 to 50 words with an automatic sending-key; but this rate is practically doubled by employing the Muirhead duplex system of sending two messages, one from each end, at the same time.

The relation of the telegraph to the telephone is analogous to that of the lower animals and man. In a telegraph circuit, with its clicking key at one end and its chattering sounder at the other, we have, in fact, an apish forerunner of the exquisite telephone, with its mysterious microphone and oracular plate. Nevertheless, the telephone descended from the telegraph in a very indirect manner, if at all, and certainly not through the sounder. The first practical suggestion of an electric telephone was made by M. Charles Bourseul, a French telegraphist, in 1854, but to all appearance nothing came of it. In 1860, however, Philipp Reis, a German schoolmaster, constructed a rudimentary telephone, by which music and a few spoken words were sent. Finally, in 1876, Mr. Alexander Graham Bell, a Scotchman, residing in Canada, and subsequently in the United States, exhibited a capable speaking telephone of his invention at the Centennial Exhibition, Philadelphia.

Figure 56 represents an outside view and section of the Bell telephone as it is now made, where M is a bar magnet having a small bobbin or coil of fine insulated wire C girdling one pole. In front of this coil there is a circular plate of soft iron capable of vibrating like a diaphragm or the drum of the ear. A cover shaped like a mouthpiece O fixes the diaphragm all round, and the wires W W serve to connect the coil in the circuit.

The soft iron diaphragm is, of course, magnetised by the induction of the pole, and would be attracted bodily to the pole were it not fixed by the rim, so that only its middle is free to move. Now, when a person speaks into the mouthpiece the sonorous waves impinge on the diaphragm and make it vibrate in sympathy with them. Being magnetic, the movement of the diaphragm to and from the bobbin excites corresponding waves of electricity in the coil, after the famous experiment of Faraday (page 64). If this undulatory current is passed through the coil of a similar telephone at the far end of the line, it will, by a reverse action, set the diaphragm in vibration and reproduce the original sonorous waves. The result is, that when another person listens at the mouthpiece of the receiving telephone, he will hear a faithful imitation of the original speech.

The Bell telephone is virtually a small magneto-electric generator of electricity, and when two are joined in circuit we have a system for the transmission of energy. As the voice is the motive power, its talk, though distinct, is comparatively feeble, and further improvements were made before the telephone became as serviceable as it is now.

Edison, in 1877, was the first to invent a working telephone, which, instead of generating the current, merely controlled the strength of it, as the sluice of a mill-dam regulates the flow of water in the lead. Du Moncel had observed that powder of carbon altered in electrical resistance under pressure, and Edison found that lamp-black was so sensitive as to change in resistance under the impact of the sonorous waves. His transmitter consisted of a button or wafer of lamp-black behind a diaphragm, and connected in the circuit. On speaking to the diaphragm the sonorous waves pressed it against the button, and so varied the strength of the current in a sympathetic manner. The receiver of Edison was equally ingenious, and consisted of a cylinder of prepared chalk kept in rotation and a brass stylus rubbing on it. When the undulatory current passed from the stylus to the chalk, the stylus slipped on the surface, and, being connected to a diaphragm, made it vibrate and repeat the original sounds. This "electro- motograph" receiver was, however, given up, and a combination of the Edison transmitter and the Bell receiver came into use.

At the end of 1877 Professor D. E. Hughes, a distinguished Welshman, inventor of the printing telegraph, discovered that any loose contact between two conductors had the property of transmitting sounds by varying the strength of an electric current passing through it. Two pieces of metal—for instance, two nails or ends of wire—when brought into a loose or crazy contact under a slight pressure, and traversed by a current, will transmit speech. Two pieces of hard carbon are still better than metals, and if properly adjusted will make the tread of a fly quite audible in a telephone connected with them. Such is the famous "microphone," by which a faint sound can be magnified to the ear.

Figure 57 represents what is known as the "pencil" microphone, in which M is a pointed rod of hard carbon, delicately poised between two brackets of carbon, which are connected in circuit with a battery B and a Bell telephone T. The joints of rod and bracket are so sensitive that the current flowing across them is affected in strength by the slightest vibration, even the walking of an insect. If, therefore, we speak near this microphone, the sonorous waves, causing the pencil to vibrate, will so vary the current in accordance with them as to reproduce the sounds of the voice in the telephone.

The true nature of the microphone is not yet known, but it is evident that the air or ether between the surfaces in contact plays an important part in varying the resistance, and, therefore, the current. In fact, a small "voltaic arc," not luminous, but dark, seems to be formed between the points, and the vibrations probably alter its length, and, consequently, its resistance. The fact that a microphone is reversible and can act as a receiver, though a poor one, tends to confirm this theory. Moreover, it is not unlikely that the slipping of the stylus in the electromotograph is due to a similar cause. Be this as it may, there can be no doubt that carbon powder and the lamp-black of the Edison button are essentially a cluster of microphones.

Many varieties of the Hughes microphone under different names are now employed as transmitters in connection with the Bell telephone. Figure 58 represents a simple micro-telephone circuit, where M is the Hughes microphone transmitter, T the Bell telephone receiver, JB the battery, and E E the earth-plates; but sometimes a return wire is used in place of the "earth." The line wire is usually of copper and its alloys, which are more suitable than iron, especially for long distances. Just as the signal currents in a submarine cable induce corresponding currents in the sea water which retard them, so the currents in a land wire induce corresponding currents in the earth, but in aerial lines the earth is generally so far away that the consequent retardation is negligible except in fast working on long lines. The Bell telephone, however, is extremely sensitive, and this induction affects it so much that a conversation through one wire can be overheard on a neighbouring wire. Moreover, there is such a thing as "self-induction" in a wire—that is to say, a current in a wire tends to induce an opposite current in the same wire, which is practically equivalent to an increase of resistance in the wire. It is particularly observed at the starting and stopping of a current, and gives rise to what is called the "extra-spark" seen in breaking the circuit of an induction coil. It is also active in the vibratory currents of the telephone, and, like ordinary induction, tends to retard their passage. Copper being less susceptible of self-induction than iron, is preferred for trunk lines. The disturbing effect of ordinary induction is avoided by using a return wire or loop circuit, and crossing the going and coming wires so as to make them exchange places at intervals. Moreover, it is found that an induction coil in the telephone circuit, like a condenser in the cable circuit, improves the working, and hence it is usual to join the battery and transmitter with the primary wire, and the secondary wire with the line and the receiver.

The longest telephone line as yet made is that from New York to Chicago, a distance of 950 miles. It is made of thick copper wire, erected on cedar poles 35 feet above the ground.

Induction is so strong on submarine cables of 50 or 100 miles in length that the delicate waves of the telephone current are smoothed away, and the speech is either muffled or entirely stifled. Nevertheless, a telephone cable 20 miles long was laid between Dover and Calais in 1891, and another between Stranraer and Donaghadee more recently, thus placing Great Britain on speaking terms with France and other parts of the Continent.

Figure 59 shows a form of telephone apparatus employed in the United Kingdom. In it the transmitter and receiver, together with a call-bell, which are required at each end of the line, are neatly combined. The transmitter is a Blake microphone, in which the loose joint is a contact of platinum on hard carbon. It is fitted up inside the box, together with an induction coil, and M is the mouthpiece for speaking to it. The receiver is a pair of Bell telephones T T, which are detached from their hooks and held to the ear. A call-bell B serves to "ring up" the correspondent at the other end of the line.

Excepting private lines, the telephone is worked on the "exchange system"—that is to say, the wires running to different persons converge in a central exchange, where, by means of an apparatus called a "switch board," they are connected together for the purpose of conversation

A telephone exchange would make an excellent subject for the artist. He delights to paint us a row of Venetian bead stringers or a band of Sevilhan cigarette makers, but why does he shirk a bevy of industrious girls working a telephone exchange? Let us peep into one of these retired haunts, where the modern Fates are cutting and joining the lines of electric speech between man and man in a great city.

The scene is a long, handsome room or gallery, with a singular piece of furniture in the shape of an L occupying the middle. This is the switchboard, in which the wires from the offices and homes of the subscribers are concentrated like the nerves in a ganglion. It is known as the "multiple switchboard," an American invention, and is divided into sections, over which the operators preside. The lines of all the subscribers are brought to each section, so that the operator can cross connect any two lines in the whole system without leaving her chair. Each section of the board is, in fact, an epitome of the whole, but it is physically impossible for a single operator to make all the connections of a large exchange, and the work is distributed amongst them. A multiplicity of wires is therefore needed to connect, say, two thousand subscribers. These are all concealed, however, at the back of the board, and in charge of the electricians. The young lady operators have nothing to do with these, and so much the better for them, as it would puzzle their minds a good deal worse than a ravelled skein of thread. Their duty is to sit in front of the board in comfortable seats at a long table and make the needful connections. The call signal of a subscriber is given by the drop of a disc bearing his number. The operator then asks the subscriber by telephone what he wants, and on hearing the number of the other subscriber he wishes to speak with, she takes up a pair of brass plugs coupled by a flexible conductor and joins the lines of the subscribers on the switchboard by simply thrusting the plugs into holes corresponding to the wires. The subscribers are then free to talk with each other undisturbed, and the end of the conversation is signalled to the operator. Every instant the call discs are dropping, the connecting plugs are thrust into the holes, and the girls are asking "Hullo! hullo!" "Are you there?" "Who are you?" "Have you finished?" Yet all this constant activity goes on quietly, deftly —we might say elegantly—and in comparative silence, for the low tones of the girlish voices are soft and pleasing, and the harsher sounds of the subscriber are unheard in the room by all save the operator who attends to him.



CHAPTER VII.

ELECTRIC LIGHT AND HEAT.

The electric spark was, of course, familiar to the early experimenters with electricity, but the electric light, as we know it, was first discovered by Sir Humphrey Davy, the Cornish philosopher, in the year 1811 or thereabout. With the magic of his genius Davy transformed the spark into a brilliant glow by passing it between two points of carbon instead of metal. If, as in figure 60, we twist the wires (+ and—) which come from a voltaic battery, say of 20 cells, about two carbon pencils, and bring their tips together in order to start the current, then draw them a little apart, we shall produce an artificial or mimic star. A sheet of dazzling light, which is called the electric arc, is seen to bridge the gap. It is not a true flame, for there is little combustion, but rather a nebulous blaze of silvery lustre in a bluish veil of heated air. The points of carbon are white-hot, and the positive is eaten away into a hollow or crater by the current, which violently tears its particles from their seat and whirls them into the fierce vortex of the arc. The negative remains pointed, but it is also worn away about half as fast as the positive. This wasting of the carbons tends to widen the arc too much and break the current, hence in arc lamps meant to yield the light for hours the sticks are made of a good length, and a self- acting mechanism feeds them forward to the arc as they are slowly consumed, thus maintaining the splendour of the illumination.

Many ingenious lamps have been devised by Serrin, Dubosq, Siemens, Brockie, and others, some regulating the arc by clockwork and electro-magnetism, or by thermal and other effects of the current. They are chiefly used for lighting halls and railway stations, streets and open spaces, search-lights and lighthouses. They are sometimes naked, but as a rule their brightness is tempered by globes of ground or opal glass. In search-lights a parabolic mirror projects all the rays in any one direction, and in lighthouses the arc is placed in the focus of the condensing lenses, and the beam is visible for at least twenty or thirty miles on clear nights. Very powerful arc lights, equivalent to hundreds of thousands of candles, can be seen for 100 or 150 miles.

Figure 61 illustrates the Pilsen lamp, in which the positive Carbon G runs on rollers rr through the hollow interior of two solenoids or coils of wire MM' and carries at its middle a spindle-shaped piece of soft iron C. The current flows through the solenoid M on its way to the arc, but a branch or shunted portion of it flows through the solenoid M', and as both of these solenoids act as electromagnets on the soft iron C, each tending to suck it into its interior, the iron rests between them when their powers are balanced. When, however, the arc grows too wide, and the current therefore becomes too weak, the shunt solenoid M' gains a purchase over the main solenoid M, and, pulling the iron core towards it, feeds the positive carbon to the arc. In this way the balance of the solenoids is readjusted, the current regains its normal strength, the arc its proper width, and the light its brilliancy.

Figure 62 is a diagrammatic representation of the Brush arc lamp. X and Y are the line terminals connecting the lamp in circuit. On the one hand, the current splits and passes around the hollow spools H H', thence to the rod N through the carbon K, the arc, the carbon K', and thence through the lamp frame to Y. On the other hand, it runs in a resistance fine-wire coil around the magnet T, thence to Y. The operation of the lamp is as follows: K and K' being in contact, a strong current starts through the lamp energising H and H', which suck in their core pieces N and S, lifting C, and by it the "washer-clutch" W and the rod N and carbon K, establishing the arc. K is lifted until the increasing resistance of the lengthening arc weakens the current in H H' and a balance is established. As the carbons burn away, C gradually lowers until a stop under W holds it horizontal and allows N to drop through W, and the lamp starts anew. If for any reason the resistance of the lamp becomes too great, or the circuit is broken, the increased current through T draws up its armature, closing the contacts M, thus short-circuiting the lamp through a thick, heavy wire coil on T, which then keeps M closed, and prevents the dead lamp from interfering with the others on its line. Numerous modifications of this lamp are in very general use.

Davy also found that a continuous wire or stick of carbon could be made white-hot by sending a sufficient current through it, and this fact is the basis of the incandescent lamp now so common in our homes.

Wires of platinum, iridium, and other inoxidisable metals raised to incandescence by the current are useful in firing mines, but they are not quite suitable for yielding a light, because at a very high temperature they begin to melt. Every solid body becomes red-hot—that is to say, emits rays of red light, at a temperature of about 1000 degrees Fahrenheit, yellow rays at 1300 degrees, blue rays at 1500 degrees, and white light at 2000 degrees. It is found, however, that as the temperature of a wire is pushed beyond this figure the light emitted becomes far more brilliant than the increase of temperature would seem to warrant. It therefore pays to elevate the temperature of the filament as high as possible. Unfortunately the most refractory metals, such as platinum and alloys of platinum with iridium, fuse at a temperature of about 3450 degrees Fahrenheit. Electricians have therefore forsaken metals, and fallen back on carbon for producing a light. In 1845 Mr. Staite devised an incandescent lamp consisting of a fine rod or stick of carbon rendered white-hot by the current, and to preserve the carbon from burning in the atmosphere, he enclosed it in a glass bulb, from which the air was exhausted by an air pump. Edison and Swan, in 1878, and subsequently, went a step further, and substituted a filament or fine thread of carbon for the rod. The new lamp united the advantages of wire in point of form with those of carbon as a material. The Edison filament was made by cutting thin slips of bamboo and charring them, the Swan by carbonising linen fibre with sulphuric acid. It was subsequently found that a hard skin could be given to the filament by "flashing" it—that is to say, heating it to incandescence by the current in an atmosphere of hydrocarbon gas. The filament thus treated becomes dense and resilient.

Figure 63 represents an ordinary glow lamp of the Edison-Swan type, where E is the filament, moulded into a loop, and cemented to two platinum wires or electrodes P penetrating the glass bulb L, which is exhausted of air.

Platinum is chosen because it expands and contracts with temperature about the same as glass, and hence there is little chance of the glass cracking through unequal stress. The vacuum in the bulb is made by a mercurial air pump of the Sprengel sort, and the pressure of air in it is only about one-millionth of an atmosphere. The bulb is fastened with a holder like that shown in figure 64, where two little hooks H connected to screw terminals T T are provided to make contact with the platinum terminals of the lamp (P, figure 63), and the spiral spring, by pressing on the bulb, ensures a good contact.

Fig. 65 is a cut of the ordinary Edison lamp and socket. One end of the filament is connected to the metal screw ferule at the base. The other end is attached to the metal button in the centre of the extreme bottom of the base. Screwing the lamp into the socket automatically connects the filament on one end to the screw, on the other to an insulated plate at the bottom of the socket.

The resistance of such a filament hot is about 200 ohms, and to produce a good light from it the battery or dynamo ought to give an electromotive force of at least 100 volts. Few voltaic cells or accumulators have an electromotive force of more than 2 volts, therefore we require a battery of 50 cells joined in series, each cell giving 2 volts, and the whole set 100 volts. The strength of current in the circuit must also be taken into account. To yield a good light such a lamp requires or "takes" about 1/2 an ampere. Hence the cells must be chosen with regard to their size and internal resistance as well as to their kind, so that when the battery, in series, is connected to the lamp, the resistance of the whole circuit, including the filament or lamp, the battery itself, and the connecting wires shall give by Ohm's law a current of 12 an ampere. It will be understood that the current has the same strength in every part of the circuit, no matter how it is made up. Thus, if 1/2 of an ampere is flowing in the lamp, it is also flowing in the battery and wires. An Edison-Swan lamp of this model gives a light of about 15 candles, and is well adapted for illuminating the interior of houses. The temperature of the carbon filament is about 3450 degrees Fahr—that is to say, the temperature at which platinum melts. Similar lamps of various sizes and shapes are also made, some equivalent to as many as 100 candles, and fitted for large halls or streets, others emitting a tiny beam like the spark of a glow-worm, and designed for medical examinations, or lighting flowers, jewels, and dresses in theatres or ball-rooms.

The electric incandescent lamp is pure and healthy, since it neither burns nor pollutes the air. It is also cool and safe, for it produces little heat, and cannot ignite any inflammable stuffs near it. Hence its peculiar merit as a light for colliers working in fiery mines. Independent of air, it acts equally well under water, and is therefore used by divers. Moreover, it can be fixed wherever a wire can be run, does not tarnish gilding, and lends itself to the most artistic decoration.

Electric lamps are usually connected in circuit on the series, parallel, and three wire system.

The series system is shown in figure 66, where the lamps L L follow each other in a row like beads on a string. It is commonly reserved for the arc lamp, which has a resistance so low that a moderate electromotive force can overcome the added resistance of the lamps, but, of course, if the circuit breaks at any point all the lamps go out.

The parallel system is illustrated in figure 67, where the lamps are connected between two main conductors cross-wise, like the steps of a ladder. The current is thus divided into cross channels, like water used for irrigating fields, and it is obvious that, although the circuit is broken at one point, say by the rupture of a filament, all the lamps do not go out.

Fig. 68 exhibits the Edison three-wire system, in which two batteries or dynamos are connected together in series, and a third or central main conductor is run from their middle poles. The plan saves a return wire, for if two generators had been used separately, four mains would have been necessary.

The parallel and three-wire systems in various groups, with or without accumulators as local reservoirs, are chiefly employed for incandescent lamps.

The main conductors conveying the current from the dynamos are commonly of stout copper insulated with air like telegraph wires, or cables coated with india-rubber or gutta-percha, and buried underground or suspended overhead. The branch and lamp conductors or "leads" are finer wires of copper, insulated with india-rubber or silk.

The current of an installation or section of one is made and broken at will by means of a "switch" or key turned by hand. It is simply a series of metal contacts insulated from each other and connected to the conductors, with a sliding contact connected to the dynamo which travels over them. To guard against an excess of current on the lamps, "cut-outs," or safety-fuses, are inserted between the switch and the conductors, or at other leading points in the circuit. They are usually made of short slips of metal foil or wire, which melt or deflagrate when the current is too strong, and thus interrupt the circuit.

There is some prospect of the luminosity excited in a vacuum tube by the alternating currents from a dynamo or an induction coil becoming an illuminant. Crookes has obtained exquisitely beautiful glows by the phosphorescence of gems and other minerals in a vacuum bulb like that shown in figure 69, where A and B are the metal electrodes on the outside of the glass. A heap of diamonds from various countries emit red, orange, yellow, green, and blue rays. Ruby, sapphire, and emerald give a deep red, crimson, or lilac phosphorescence, and sulphate of zinc a magnificent green glow. Tesla has also shown that vacuum bulbs can be lit inside without any outside connection with the current, by means of an apparatus like that shown in figure 70, where D is an alternating dynamo, C a condenser, P S the primary and secondary coils of a sparking transformer, T T two metal sheets or plates, and SB the exhausted bulbs. The alternating or see-saw current in this case charges the condenser and excites the primary coil P, while the induced current in the secondary coil 5 charges the terminal plates T T. So long as the bulbs or tubes are kept within the space between the plates, they are filled with a soft radiance, and it is easy to see that if these plates covered the opposite walls of a room, the vacuum lamps would yield a light in any part of it.

Electric heating bids fair to become almost as important as electric illumination. When the arc was first discovered it was noticed that platinum, gold, quartz, ruby, and diamond—in fine, the most refractory minerals—were melted in it, and ran like wax. Ores and salts of the metals were also vapourised, and it was clear that a powerful engine of research had been placed in the hands of the chemist. As a matter of fact, the temperature of the carbons in the arc is comparable to that of the Sun. It measures 5000 to 10,000 degrees Fahrenheit, and is the highest artificial heat known. Sir William Siemens was among the first to make an electric furnace heated by the arc, which fused and vapourised metallic ores, so that the metal could be extracted from them. Aluminium, chromium, and other valuable metals are now smelted by its means, and rough brilliants such as those found in diamond mines and meteoric stones have been crystallised from the fumes of carbon, like hoar frost in a cold mist.

The electric arc is also applied to the welding of wires, boiler plates, rails, and other metal work, by heating the parts to be joined and fusing them together.

Cooking and heating by electricity are coming more and more into favour, owing to their cleanliness and convenience. Kitchen ranges, including ovens and grills, entirely heated by the electric current, are finding their way into the best houses and hotels. Most of these are based on the principle of incandescence, the current heating a fine wire or other conductor of high resistance in passing through it. Figure 71 represents an electric kettle of this sort, which requires no outside fire to boil it, since the current flows through fine wires of platinum or some highly resisting metal embedded in fireproof insulating cement in its bottom. Figures 72 and 73 are a sauce-pan and a flat-iron heated in the same way. Figure 74 is a cigar-lighter for smoking rooms, the fusee F consisting of short platinum wires, which become red-hot when it is unhooked, and at the same time the lamp Z is automatically lit. Figure 75 is an electric radiator for heating rooms and passages, after the manner of stoves and hot water pipes. Quilts for beds, warmed by fine wires inside, have also been brought out, a constant temperature being maintained by a simple regulator, and it is not unlikely that personal clothing of the kind will soon be at the service of invalids and chilly mortals, more especially to make them comfortable on their travels.

An ingenious device places an electric heater inside a hot water bag, thus keeping it at a uniform temperature for sick-room and hospital use.



CHAPTER VIII.

ELECTRIC POWER.

On the discovery of electromagnetism (Chap. IV.), Faraday, Barlow, and others devised experimental apparatus for producing rotary motion from the electric current, and in 1831, Joseph Henry, the famous American electrician, invented a small electromagnetic engine or motor. These early machines were actuated by the current from a voltaic battery, but in the middle of the century Jacobi found that a dynamo-electric generator can also work as a motor, and that by coupling two dynamos in circuit—one as a generator, the other as a motor—it was possible to transmit mechanical power to any distance by means of electricity. Figure 76 is a diagram of a simple circuit for the transmission of power, where D is the technical symbol for a dynamo as a generator, having its poles (+ and -) connected by wire to the poles of M, the distant dynamo, as a motor. The generator D is driven by mechanical energy from any convenient source, and transforms it into electric energy, which flows through the circuit in the direction of the arrows, and, in traversing the motor M, is re-transformed into mechanical energy. There is, of course, a certain waste of energy in the process, but with good machines and conductors, it is not more than 10 to 25 per cent., or the "efficiency" of the installation is from 75 to 90 per cent—that is to say, for every 100 horse-power put into the generator, from 75 to 90 horse-power are given out again by the motor.

It was not until 1870, when Gramme had improved the dynamo, that power was practically transmitted in this way, and applied to pumping water, and other work. Since then great progress has been made, and electricity is now recognised, not only as a rival of steam, but as the best means of distributing steam, wind, water, or any other power to a distance, and bringing it to bear on the proper point.

The first electric railway, or, rather, tramway, was built by Dr. Werner von Siemens at Berlin in 1879, and was soon followed by many others. The wheels of the car were driven by an electric motor drawing its electricity from the rails, which were insulated from the ground, and being connected to the generator, served as conductors. It was found very difficult to insulate the rails, and keep the electricity from leaking to the ground, however, and at the Pans Electrical Exhibition of 1881, von Siemens made a short tramway in which the current was drawn from a bare copper conductor running on poles, like a telegraph wire, along the line.

The system will be understood from figure 77, where L is the overhead conductor joined to the positive pole of the dynamo or generator in the power house, and C is a rolling contact or trolley wheel travelling with the car and connected by the wire W to an electric motor M under the car, and geared to the axles. After passing through the motor the current escapes to the rail R by a brush or sliding contact C', and so returns to the negative pole of the generator. A very general way is to allow the return current to escape to the rails through the wheels. Many tramways, covering thousands of miles, are now worked on this plan in the United States. At Bangor, Maine, a modification of it is in use whereby the conductor is divided into sections, alternately connected to the positive and negative poles of two generators, coupled together as in the "three-wire system" of electric lighting (page 119), their middle poles being joined to the earth —that is to say, the rails. It enables two cars to be run on the same line at once, and with a considerable saving of copper.

To make the car independent of the conductor L for a short time, as in switching, a battery of accumulators B may be added and charged from the conductor, so that when the motor is disconnected from the conductor, the discharge from the accumulator may still work it and drive the wheels.

Attempts have been made to run tramcars with the electricity supplied by accumulators alone, but the system is not economical owing to the dead weight of the cells, and the periodical trouble of recharging them at the generating station.

On heavy railroads worked by electricity the overhead conductor is replaced by a third rail along the middle of the track, and insulated from the ground In another system the middle conductor is buried underground, and the current is tapped at intervals by the motor connecting with it for a moment by means of spring contacts as the car travels In each case, however, the outer rails serve as the return conductors

Another system puts one or both the conductors in a conduit underground, the trolley pole entering through a narrow slot similar to that used on cable roads

The first electric carriages for ordinary roads were constructed in 1889 by Mr. Magnus Volk of Brighton. Figure 78 represents one of these made for the Sultan of Turkey, and propelled by a one- horse-power Immisch electric motor, geared to one of the hind wheels by means of a chain. The current for the motor was supplied by thirty "EPS" accumulators stowed in the body of the vehicle, and of sufficient power to give a speed of ten miles an hour. The driver steers with a hand lever as shown, and controls the speed by a switch in front of him.

Vans, bath chairs, and tricycles are also driven by electric motors, but the weight of the battery is a drawback to their use.

In or about the year 1839, Jacobi sailed an electric boat on the Neva, with the help of an electromagnetic engine of one horse- power, fed by the current from a battery of Grove cells, and in 1882 a screw launch, carrying several passengers, and propelled by an electric motor of three horse-power, worked by forty-five accumulators, was tried on the Thames. Being silent and smokeless in its action, the electric boat soon came into favour, and there is now quite a flotilla on the river, with power stations for charging the accumulators at various points along the banks.

Figure 79 illustrates the interior of a handsome electric launch, the Lady Cooper, built for the "E P S," or Electric Power Storage Company. An electric motor in the after part of the hull is coupled directly to the shaft of the screw propeller, and fed by "E P S" accumulators in teak boxes lodged under the deck amidships. The screw is controlled by a switch, and the rudder by an ordinary helm. The cabin is seven feet long, and lighted by electric lamps. Alarm signals are given by an electric gong, and a search-light can be brought into operation whenever it is desirable. The speed attained by the Lady Cooper is from ten to fifteen knots.

M. Goubet, a Frenchman, has constructed a submarine boat for discharging torpedoes and exploring the sea bottom, which is propelled by a screw and an electric motor fed by accumulators. It can travel entirely under water, below the agitation of the waves, where sea-sickness is impossible, and the inventor hopes that vessels of the kind will yet carry passengers across the Channel.

The screw propeller of the Edison and Sim's torpedo is also driven by an electric motor. In this case the current is conveyed from the ship or fort which discharges the torpedo by an insulated conductor running off a reel carried by the torpedo, the "earth" or return half of the circuit being the sea-water.

All sorts of machinery are now worked by the electric motor—for instance, cranes, elevators, capstans, rivetters, lathes, pumps, chaff-cutters, and saws. Of domestic appliances, figure 80 shows an air propeller or ventilation fan, where F is a screw-like fan attached to the spindle of the motor M, and revolving with its armature. Figure 81 represents a Trouve motor working a sewing- machine, where N is the motor which gears with P the driving axle of the machine. Figure 82 represents a fine drill actuated by a Griscom motor. The motor M is suspended from a bracket A B C by the tackle D E, and transmits the rotation of its armature by a flexible shaft S T to the terminal drill O, which can be applied at any point, and is useful in boring teeth.

Now that electricity is manufactured and distributed in towns and villages for the electric light, it is more and more employed for driving the lighter machinery. Steam, however, is more economical on a large scale, and still continues to be used in great factories for the heavier machinery. Nevertheless a day is coming when coal, instead of being carried by rail to distant works and cities, will be burned at the pit mouth, and its heat transformed by means of engines and dynamos into electricity for distribution to the surrounding country. I have shown elsewhere that peat can be utilised in a similar manner, and how the great Bog of Allen is virtually a neglected gold field in the heart of Ireland. [Footnote: The Nineteenth Century for December 1894.] The sunshine of deserts, and perhaps the electricity of the atmosphere, but at all events the power of winds, waves, and waterfalls are also destined to whirl the dynamo, and yield us light, heat, or motion. Much has already been done in this direction. In 1891 the power of turbines driven by the Falls of Neckar at Lauffen was transformed into electricity, and transmitted by a small wire to the Electrical Exhibition of Frankfort-on-the-Main, 117 miles away. The city of Rome is now lighted from the Falls of Tivoli, 16 miles distant. The finest cataract in Great Britain, the Falls of Foyers, in the Highlands, which persons of taste and culture wished to preserve for the nation, is being sacrificed to the spirit of trade, and deprived of its waters for the purpose of generating electricity to reduce aluminium from its ores.

The great scheme recently completed for utilizing the power of Niagara Falls by means of electricity is a triumph of human enterprise which outrivals some of the bold creations of Jules Verne.

When in 1678 the French missionaries La Salle and Hennepin discovered the stupendous cataract on the Niagara River between Lake Ontario and Lake Erie, the science of electricity was in its early infancy, and little more was known about the mysterious force which is performing miracles in our day than its manifestation on rubbed amber, sealing-wax, glass, and other bodies. Nearly a hundred years had still to pass ere Franklin should demonstrate the identity of the electric fire with lightning, and nearly another hundred before Faraday should reveal a mode of generating it from mechanical power. Assuredly, neither La Salle nor his contemporaries ever dreamed of a time when the water-power of the Falls would be distributed by means of electricity to produce light or heat and serve all manner of industries in the surrounding district. The awestruck Iroquois Indians had named the cataract "Oniagahra," or Thunder of the Waters, and believed it the dwelling-place of the Spirit of Thunder. This poetical name is none the less appropriate now that the modern electrician is preparing to draw his lightnings from its waters and compel the genius loci to become his willing bondsman.

The Falls of Niagara are situated about twenty-one miles from Lake Erie, and fourteen miles from Lake Ontario. At this point the Niagara River, nearly a mile broad, flowing between level banks, and parted by several islands, is suddenly shot over a precipice 170 feet high, and making a sharp bend to the north, pursues its course through a narrow gorge towards Lake Ontario. The Falls are divided at the brink by Goat Island, whose primeval woods are still thriving in their spray. The Horseshoe Fall on the Canadian side is 812 yards, and the American Falls on the south side are 325 yards wide. For a considerable distance both above and below the Falls the river is turbulent with rapids.

The water-power of the cataract has been employed from olden times. The French fur-traders placed a mill beside the upper rapids, and the early British settlers built another to saw the timher used in their stockades. By-and-by, the Stedman and Porter mills were established below the Falls; and subsequently, others which derived their water-supply from the lower rapids by means of raceways or leads. Eventually, an open hydraulic canal, three- fourths of a mile long, was cut across the elbow of land on the American side, through the town of Niagara Falls, between the rapids above and the verge of the chasm below the Falls, where, since 1874, a cluster of factories has arisen, which discharge their spent water over the cliff in a series of cascades almost rivalling Niagara itself. This canal, which only taps a mere drop from the ocean of power that is running to waste, has been utilised to the full; and the decrease of water-privileges in the New England States, owing to the clearing of the forests and settlement of the country, together with the growth of the electrical industries, have led to a further demand on the resources of Niagara.

With the example of Minneapolis, which draws the power for its many mills from the Falls of St. Anthony, in the Mississippi River, before them, a group of far-seeing and enterprising citizens of Niagara Falls resolved to satisfy this requirement by the foundation of an industrial city in the neighbourhood of the Falls. They perceived that a better site could nowhere be found on the American Continent. Apart from its healthy air and attractive scenery, Niagara is a kind of half-way house between the East and West, the consuming and the producing States. By the Erie Canal at Tonawanda it commands the great waterway of the Lakes and the St. Lawrence. A system of trunk railways from different parts of the States and Canada are focussed there, and cross the river by the Cantilever and Suspension bridges below the Falls. The New York Central and Hudson River, the Lehigh Valley, the Buffalo, Rochester, and Pittsburgh, the Michigan Central, and the Grand Trunk of Canada, are some of these lines. Draining as it does the great lakes of the interior, which have a total area of 92,000 square miles, with an aggregate basin of 290,000 square miles, the volume of water in the Niagara River passing over the cataract every second is something like 300,000 cubic feet; and this, with a fall of 276 feet from the head of the upper rapids to the whirlpool rapids below, is equivalent to about nine million, or, allowing for waste in the turbines, say, seven million horse- power. Moreover, the great lakes discharging—into each other form a chain of immense reservoirs, and the level of the river being little affected by flood or drought, the supply of pure water is practically constant all the year round. Mr. R. C. Reid has shown that a rainfall of three inches in twenty-four hours over the basin of Lake Superior would take ninety days to run off into Lake Huron, which, with Lake Michigan, would take as long to overflow into Lake Erie; and, therefore, six months would elapse before the full effect of the flood was expended at the Falls.

The first outcome of the movement was the Niagara River Hydraulic Power and Sewer Company, incorporated in 1886, and succeeded by the Niagara Falls Power Company. The old plan of utilising the water by means of an open canal was unsuited to the circumstances, and the company adopted that of the late Mr. Thomas Evershed, divisional engineer of the New York State Canals. Like the other, it consists in tapping the river above the Falls, and using the pressure of the water to drive the number of turbines, then restoring the water to the river below the Falls; but instead of a surface canal, the tail-race is a hydraulic tunnel or underground conduit. To this end some fifteen hundred acres of spare land, having a frontage just above the upper rapids, was quietly secured at the low price of three hundred dollars an acre; and we believe its rise in value owing to the progress of the works is such that a yearly rental of two hundred dollars an acre can even now be got for it. This land has been laid out as an industrial city, with a residential quarter for the operatives, wharves along the river, and sidings or short lines to connect with the trunk railways. In carrying out their purpose the company has budded and branched into other companies—one for the purchase of the land; another for making the railways; and a third, the Cataract Construction Company, which is charged with the carrying out of the engineering works, for the utilisation of the water-power, and is therefore the most important of all. A subsidiary company has also been formed to transmit by electricity a portion of the available power to the city of Buffalo, at the head of the Niagara River, on Lake Erie, some twenty miles distant. All these affiliated bodies are, however, under the directorate of the Cataract Construction Company; and amongst those who have taken the most active part in the work we may mention the president, Mr. E. D. Adams; Professor Coleman Sellers, the consulting engineer; and Professor George Forbes, F. R. S., the consulting electrical engineer, a son of the late Principal Forbes of Edinburgh.

In securing the necessary right of way for the hydraulic tunnel or in the acquisitom of land, the Company has shown consummate tact. A few proprietors declined to accept its terms, and the Company selected a parallel route. Having obtained the right of way for the latter, it informed the refractory owners on the first line of their success, and intimated that the Company could now dispense with that. On this the sticklers professed their willingness to accept the original terms, and the bargain was concluded, thus leaving the Company in possession of the rights of way for two tunnels, both of which they propose to utilise.

The liberal policy of the directors is deserving of the highest commendation. They have risen above mere "chauvinism," and instead of narrowly confining the work to American engineers, they have availed themselves of the best scientific counsel which the entire world could afford. The great question as to the best means of distributing and applying the power at their command had to be settled; and in 1890, after Mr. Adams and Dr. Sellers had made a visit of inspection to Europe, an International Commission was appointed to consider the various methods submitted to them, and award prizes to the successful competitors. Lord Kelvin (then Sir William Thomson) was the president, and Professor W. C. Unwin, the well-known expert in hydraulic engineering, the secretary, while other members were Professor Mascart of the Institute, a leading French electrician; Colonel Turretini of Geneva, and Dr. Sellers. A large number of schemes were sent in, and many distinguished engineers gave evidence before the Commission. The relative merits of compressed air and electricity as a means of distributing the power were discussed, and on the whole the balance of opinion was in favour of electricity. Prizes of two hundred and two hundred and fifty pounds were awarded to a number of firms who had submitted plans, but none of these were taken up by the Company. The impulse turbines of Messrs. Faesch & Piccard, of Geneva, who gained a prize of two hundred and fifty pounds, have, however, been adopted since. It is another proof of the determination of the Company to procure the best information on the subject, regardless of cost, that Professor Forbes had carte blanche to go to any part of the world and make a report on any system of electrical distribution which he might think fit.

With the selection of electricity another question arose as to the expediency of employing continuous or alternating currents. At that time continuous currents were chiefly in vogue, and it speaks well for the sagacity and prescience of Professor Forbes that he boldly advocated the adoption of alternating currents, more especially for the transmission of power to Buffalo. His proposals encountered strong opposition, even in the highest quarters; but since then, partly owing to the striking success of the Lauffen to Frankfort experiment in transmitting power by alternating currents over a bare wire on poles a distance of more than a hundred miles, the directors and engineers have come round to his view of the matter, and alternating currents have been employed, at all events for the Buffalo line, and also for the chief supply of the industrial city. Continuous currents, flowing always in the same direction, like the current of a battery, can, it is true, be stored in accumulators, but they cannot be converted to higher or lower pressure in a transformer. Alternating currents, on the other hand, which see-saw in direction many times a second, cannot be stored in accumulators, but they can be sent at high pressure along a very fine wire, and then converted to higher or lower pressures where they are wanted, and even to continuous currents. Each kind, therefore, has its peculiar advantages, and both will be employed to some extent.

With regard to the engineering works, the hydraulic tunnel starts from the bank of the river where it is navigable, at a point a mile and a half above the Falls, and after keeping by the shore, it cuts across the bend beneath the city of Niagara Falls, and terminates below the Suspension Bridge under the Falls at the level of the water. It is 6700 yards long, and of a horseshoe section, 19 feet wide by 21 feet high. It has been cut 160 feet below the surface through the limestone and shale, but is arched with brick, having rubble above, and at the outfall is lined on the invert or under side with iron. The gradient is 36 feet in the mile, and the total fall is 205 feet, of which 140 feet are available for use. The capacity of the tunnel is 100,000 horse- power. In the lands of the company it is 400 feet from the margin of the river, to which it is connected by a canal, which is over 1500 feet long, 500 feet wide at the mouth, and 12 feet deep.

Out of this canal, head-races fitted with sluices conduct the water to a number of wheel-pits 160 feet deep, which have been dug near the edge of the canal, and communicate below with the tunnel. At the bottom of each wheel-pit a 5000 horse-power Girard double turbine is mounted on a vertical shaft, which drives a propeller shaft rising to the surface of the ground; a dynamo of 5000 horse- power is fixed on the top of this shaft, and so driven by it. The upward pressure of the water is ingeniously contrived to relieve the foundation of the weight of the turbine shaft and dynamo. Twenty of these turbines, which are made by the I. P. Morris Company of Philadelphia, from the designs of Messrs. Faesch and Piccard, will be required to utilize the full capacity of the tunnel.

The company possesses a strip of land extending two miles along the shore; and in excavating the tunnel a coffer-dam was made with the extracted rock, to keep the river from flooding the works. This dam now forms part of a system by which a tract of land has been reclaimed from the river. Part of it has already been acquired by the Niagara Paper Pulp Company, which is building gigantic factories, and will employ the tailrace or tunnel of the Cataract Construction Company. Wharfs for the use of ships and canal boats will also be constructed on this frontage. By land and water the raw materials of the West will be conveyed to the industrial town which is now coming into existence; grain from the prairies of Illinois and Dakota; timber from the forests of Michigan and Wisconsin; coal and copper from the mines of Lake Superior; and what not. It is expected that one industry having a seat there will attract others. Thus, the pulp mills will bring the makers of paper wheels and barrels; the smelting of iron will draw foundries and engine works; the electrical refining of copper will lead to the establishment of wire-works, cable factories, dynamo shops, and so on. Aluminum, too, promises to create an important industry in the future. In the meantime, the Cataract Construction Company is about to start an electrical factory of its own, which will give employment to a large number of men. It has also undertaken the water supply of the adjacent city of Niagara Falls. The Cataract Electric Company of Buffalo has obtained the exclusive right to use the electricity transmitted to that city, and the line will be run in a subway. This underground line will be more expensive to make than an overhead line, but it will not require to be renewed every eight to fifteen years, and it will not be liable to interruption from the heavy gales that sweep across the lakes, or the weight of frozen sleet: moreover, it will be more easily inspected, and quite safe for the public. We should also add that, in addition to the contemplated duplicate tunnel of 100,000 horse-power, the Cataract Construction Company owns a concession for utilising 250,000 horse-power from the Horseshoe Falls on the Canadian side in the same manner. It has thus a virtual monopoly of the available water-power of Niagara, and the promoters have not the least doubt that the enterprise will be a great financial success. Already the Pittsburg Reduction Company have begun to use the electricity in reducing aluminum from the mineral known as bauxite, an oxide of the metal, by means of the electric furnace.

Another portion of the power is to be used to produce carbide of calcium for the manufacture of acetylene gas. At a recent electrical exhibition held in New York city a model of the Niagara plant was operated by an electric current brought from Niagara, 450 miles distant; and a collection of telephones were so connected that the spectator could hear the roar of the real cataract.

Thanks to the foresight of New York State and Canada, the scenery of the Falls has been preserved by the institution of public parks, and the works in question will do nothing to spoil it, especially as they will be free from smoke. Mr. Bogarts, State Engineer of New York, estimates that the water drawn from the river will only lower the mean depth of the Falls about two inches, and will therefore make no appreciable difference in the view. Altogether, the enterprise is something new in the history of the world. It is not only the grandest application of electrical power, but one of the most remarkable feats in an age when romance has become science, and science has become romance.



CHAPTER IX.

MINOR USES OF ELECTRICITY.

The electric "trembling bell," now in common use, was first invented by John Mirand in 1850. Figure 83 shows the scheme of the circuit, where

B is a small battery, say two or three "dry" or Leclanche cells, joined by insulated wire to P, a press-button or contact key, and G an electromagnetic gong or bell. On pressing the button P, a spring contact is made, and the current flowing through the circuit strikes the bell. The action of the contact key will be understood from figure 84, where P is the press-button removed to show the underlying mechanism, which is merely a metal spring A over a metal plate B. The spring is connected by wire to a pole of the battery, and the plate to a terminal or binding screw of the bell, or vice versa. When the button P is pressed by the finger the spring is forced against the plate, the circuit is made, and the bell rings. On releasing the button it springs back, the circuit is broken, and the bell stops.

Figure 85 shows the inner mechanism of the bell, which consists of a double-poled electromagnet M, having a soft iron armature A hinged on a straight spring or tongue S, with one end fixed, and the other resting against a screw contact T. The hammer H projects from the armature beside the edge of the gong E.

In passing through the instrument the current proceeds from one terminal, say that on the right, by the wire W to the screw contact T, and thence by the spring S through the bobbins of the electromagnet to the other terminal. The electromagnet attracts the armature A, and the hammer H strikes the gong; but in the act the spring S is drawn from the contact T, and the circuit is broken. Consequently the electromagnet, no longer excited, lets the armature go, and the spring leaps back against the contact T, withdrawing the hammer from the gong. But the instrument is now as it was at first, the current again flows, and the hammer strikes the gong, only to fly back a second time. In this way, as long as the button is pressed by the operator, the hammer will continue to tap the bell and give a ringing sound. Press-buttons are of various patterns, and either affixed to the wall or inserted in the handle of an ordinary bell-pull, as shown in figure 86.

The ordinary electric bell actuated by a battery is liable to get out of order owing to the battery spending its force, or to the contacts becoming dirty. Magnetoelectric bells have, therefore, been introduced of late years. With these no battery or interrupting contacts are required, since the bell-pull or press- button is made in the form of a small dynamo which generates the current when it is pulled or pushed. Figure 87 illustrates a form of this apparatus, where M P is the bell-pull and B the bell, these being connected by a double wire W, to convey the current. The bell-pull consists of a horseshoe magnet M, having a bobbin of insulated wire between its poles, and mounted on a spindle. When the key P is turned round by the hand, the bobbin moves in the magnetic field between the poles of the magnet, and the current thus generated circulates in the wires W, and passing through an electromagnet under the bell, attracts its armature, and strikes the hammer on the bell. Of course the bell may be placed at any distance from the generator. In other types the current is generated and the bell rung by the act of pulling, as in a common house-bell.

Electric bells in large houses and hotels are usually fitted up with indicators, as shown in figure 88, which tell the room from which the call proceeds. They are serviceable as instantaneous signals, annunciators, and alarms in many different ways. An outbreak of fire can be announced by causing the undue rise of temperature to melt a piece of tallow or fusible metal, and thus release a weight, which tails on a press-button, and closes the circuit of an electric bell. Or, the rising temperature may expand the mercury in a tube like that of a thermometer until it connects two platinum wires fused through the glass and in circuit with a bell. Some employ a curving bi-metallic spring to make the necessary contact. The spring is made by soldering strips of brass and iron back to back, and as these metals expand unequally when heated, the spring is deformed, and touches the contact which is connected in the circuit, thus permitting the current to ring the bell. A still better device, however, is a small box containing a thin metallic diaphragm, which expands with the heat, and sagging in the centre, touches a contact screw, thus completing the circuit, and allowing the current to pass.