The receiving instrument used by Messrs. Pollak & Virag in their high-speed system of telegraphy. This instrument is capable of receiving and photographically recording messages at the astonishing speed of 50,000 words an hour.
The receiving instrument used by Messrs. Pollak & Virag in their high-speed system of telegraphy. This instrument is capable of receiving and photographically recording messages at the astonishing speed of 50,000 words an hour.
The Bain Chemical Telegraph was able to transmit the enormous number of 1500 words per minute; that is, at ten times the rate of ordinary conversation! But even when improvements had reduced the line wires from five to one, the system, on account of the method of composing the message to be sent, was not found sufficiently practical to come into general use.
Its place was taken by slower but preferable systems: those of duplex and multiplex telegraphy.
When a message is sent over the wires, the actual time of making the signals is more than is required for the current to pass from place to place. This fact has been utilised by the inventors of methods whereby two or more messages may not only be sent thesameway along the same wire, but may also besent indifferentdirections. Messages are “duplex” when they travel across one another, “multiplex” when they travel together.
The principle whereby several instruments are able to use the same wire is that ofdistributingamong the instruments the time during which they are in contact with the line.
Let us suppose that four transmitters are sending messages simultaneously from London to Edinburgh.
Wires from all four instruments are led into a circular contact-maker, divided into some hundreds of insulated segments connected in rotation with the four transmitters. Thus instrument A will be joined to segments 1, 5, 9, 13; instrument B to segments 2, 6, 10, 14; instrument C with segments 3, 7, 11, 15; and so on.
Along the top of the segments an arm, connected with the telegraph line to Edinburgh, revolves at a uniform rate. For about 1/500 of a second it unites a segment with an instrument. If there are 150 segments on the “distributor,” and the arm revolves three times a second, each instrument will be put into contact with the line rather oftener than 110 times per second. And if the top speed of fifty words a minute is being worked to, each of the fifteen signals occurring in each second will be on the average divided among seven moments of contact.
A similar apparatus at Edinburgh receives the messages. It is evident that for the system to work satisfactorily, or even to escape dire confusion, therevolving arms must run at a level speed in perfect unison with one another. When the London arm is over segment 1, the Edinburgh arm must cover the same number. The greatest difficulty in multiplex telegraphy has been to adjust the timing exactly.
Paul la Cour of Copenhagen invented for driving the arms a device called the Phonic Wheel, as its action was regulated by the vibrations of a tuning-fork. The wheel, made of soft iron, and toothed on its circumference, revolves at a short distance from the pole of a magnet. As often as a current enters the magnet the latter attracts the nearest tooth of the wheel; and if a regular series of currents pass through it the motion of the wheel will be uniform. M. la Cour produced the regularity of current impulses in the motor magnet by means of a tuning-fork, which is unable to vibrate more than a certain number of times a second, and at each vibration closed a circuit sending current into the magnet. To get two tuning-forks of the same note is an easy matter; and consequently a uniformity of rotation at both London and Edinburgh stations may be insured.
So sensitive is this “interrupter” system that as many as sixteen messages can be sent simultaneously, which means that a single wire is conveying from 500 to 800 words a minute. We can easily understand the huge saving that results from such a system; the cost of instruments, interrupter, &c., being butsmall in proportion to that of a number of separate conductors.
The word-sending capacity of a line may be even further increased by the use of automatic transmitters able to work much faster in signal-making than the human brain and hand. Sir Charles Wheatstone’s Automatic Transmitter has long been used in the Post-Office establishments.
The messages to be sent are first of all punched on a long tape with three parallel rows of perforations. The central row is merely for guiding the tape through the transmitting machine. The positions of the holes in the two outside rows relatively to each other determine the character of the signal to be sent. Thus, when three holes (including the central one) are abreast, a Morse “dot” is signified; when the left-hand hole is one place behind the right hand, a “dash” will be telegraphed.
In the case of a long communication the matter is divided among a number of clerks operating punching machines. Half-a-dozen operators could between them punch holes representing 250 to 300 words a minute; and the transmitter is capable of despatching as many in the same time, while it has the additional advantage of being tireless.
The action of the transmitter is based upon the reversal of the direction or nature of current. The punched tape is passed between an oscillating lever, carrying two points, and plates connected with thetwo poles of the battery. As soon as a hole comes under a pin the pin drops through and makes a contact.
At the receiving end the wire is connected with a coil wound round the pole of a permanent bar-magnet. Such a magnet has what is known as a north pole and a south pole, the one attractive and the other repulsive of steel or soft iron. Any bar of soft iron can be made temporarily into a magnet by twisting round it a few turns of a wire in circuit with the poles of a battery. But which will be the north and which the south pole depends on thedirectionof the current. If, then, a current passes in one direction round the north pole of a permanent magnet it will increase the magnet’s attractive power, but will decrease it if sent in the other direction.
The “dot” holes punched in the tape being abreast cause first a positive and then a negative current following at a very short interval; but the “dash” holes not being opposite allow the positive current to occupy the wires for a longer period. Consequently the Morse marker rests for correspondingly unequal periods on the recording “tape,” giving out a series of dots and dashes, as the inker is snatched quickly or more leisurely from the paper.
The Wheatstone recorder has been worked up to 400 words a minute, and when two machines are by the multiplex method acting together this rate is of course doubled.
As a speed machine it has, however, been completelyput in the shade by a more recent invention of two Hungarian electricians, Anton Pollak and Josef Virag, which combines the perforated strip method of transmission with the telephone and photography. The message is sent off by means of a punched tape, and is recorded by means of a telephonic diaphragm and light marking a sensitised paper.
In 1898 the inventors made trials of their system for the benefit of the United Electrical Company of Buda-Pesth. The Hungarian capital was connected by two double lines of wire with a station 200 miles distant, where the two sets were joined so as to give a single circuit of 400 miles in length. A series of tests in all weathers showed that the Pollak-Virag system could transmit as many as 100,000 words an hour over that distance.
From Hungary the inventors went to the United States, in which country of “records” no less than 155,000 words were despatched and received in the sixty minutes. This average—2580 words per minute, 43 per second—is truly remarkable! Even between New York and Chicago, separated by 950 odd miles, the wires kept up an average of 1000 per minute.
The apparatus that produces these marvellous results is of two types. The one type records messages in the Morse alphabet, the other makes clearly-written longhand characters. The former is the faster of the two, but the legibility of the other more than compensates for the decrease of speed by one-half.
Specimens of the punched tape used for transmitting messages by the Pollak-Virag system, and of a message as it is delivered by the receiving machine.
Specimens of the punched tape used for transmitting messages by the Pollak-Virag system, and of a message as it is delivered by the receiving machine.
The Morse alphabet method closely resembles the Wheatstone system. The message is prepared for transmission by being punched on a tape. But there is this difference in the position of the holes, that whereas in the Wheatstone method two holes are used for each dot and dash, only one is required in the Pollak-Virag. If to the right of the central guiding line it signifies a “dash,” if to the left, a “dot.”
The “reversal-of-current” method, already explained, causes at the receiver end an increase or decrease in the power of a permanent magnet to attract or repel a diaphragm, the centre of which is connected by a very fine metal bar with the centre of a tiny mirror hinged at one side on two points. A very slight movement of the diaphragm produces an exaggerated movement of the mirror, which, as it tilts backwards and forwards, reflects the light from an electric lamp on to a lens, which concentrates the rays into a bright spot, and focuses them on to a surface of sensitised paper.
In their earliest apparatus the inventors attached the paper to the circumference of a vertical cylinder, which revolved at an even pace on an axle, furnished at the lower end with a screw thread, so that the portion of paper affected by the light occupied a spiral path from top to bottom of the cylinder.
In a later edition, however, an endless band of sensitised paper is employed, and the lamp is screened from the mirror by a horizontal mantle in which iscut a helical slit making one complete turn of the cylinder in its length. The mantle is rotated in unison with the machinery driving the sensitised band; and as it revolves, the spot at which the light from the filament can pass through the slit to the mirror is constantly shifting from right to left, and the point at which the reflected light from the mirror strikes the sensitised paper from left to right. At the moment when a line is finished, the right extremity of the mantle begins to pass light again, and the bright spot of light recommences its work at the left edge of the band, which has now moved on a space.
The movements of the mirror backwards and forwards produce on the paper a zigzag tracing known as syphon-writing. The record, which is continuous from side to side of the band, is a series of zigzag up-and-down strokes, corresponding to the dots and dashes of the Morse alphabet.
The apparatus for transmitting longhand characters is more complicated than that just described. Two telephones are now used, and the punched tape has in it five rows of perforations.
If we take a copy-book and examine the letters, we shall see that they all occupy one, two, or three bands of space. For instance,a, between the lines, occupies one band;g, two bands; andf, three. In forming letters, the movements of the fingers trace curves and straight lines, the curves being the resultants of combined horizontal and vertical movements.
Messrs. Pollak and Virag, in order to producecurves, were obliged to add a second telephone, furnished also with a metal bar joined to the mirror, which rests on three points instead of on two. One of these points is fixed, the other two represent the ends of the two diaphragm bars, which move the mirror vertically and horizontally respectively, either separately or simultaneously.
A word about the punched paper before going further. It contains, as we have said, five rows of perforations. The top three of these are concerned only with the up-and-down strokes of the letters, the bottom two with the cross strokes. When a hole of one set is acting in unison with a hole of the other set a composite movement or curve results.
The topmost row of all sends through the wires a negative current of known strength; this produces upward and return strokes in the upper zone of the letters: for instance, the upper part of at. The second row passespositivecurrents of equal strength with the negative, and influences the up-and-down strokes of the centre zone,e.g.those ofo; the third row passes positive currentstwiceas strong as the negative, and is responsible for double-length vertical strokes in the centre and lower zones,e.g.the stroke inp.
In order that the record shall not be a series of zigzags it is necessary that the return strokes in the vertical elements shall be on the same path as the out strokes; and as the point of light is continuously tending to move from left to right of the paper theremust at times be present a counteracting tendency counterbalancing it exactly, so that the path of the light point is purely vertical. At other times not merely must the horizontal movements balance each other, but the right-to-left element must be stronger than the left-to-right, so that strokes such as the left curve of anemay be possible. To this end rows 4 and 5 of the perforations pass currents working the second telephone diaphragm, which moves the mirror on a vertical axis so that it reflects the ray horizontally.
It will be noticed that the holes in rows 3, 4, 5 vary in size to permit the passage of currents during periods of different length. In this manner the little junction-hooks of such letters asr,w,v,bare effected.
As fast as the sensitised paper strip is covered with the movements of the dancing spot of light it is passed on over rollers through developing and fixing chemical baths; so that the receiving of messages is purely automatic.
The reader can judge for himself the results of this ingenious system as shown in a short section of a message transmitted by Mr. Pollak. The words shown actually occupied two seconds in transmission. They are beautifully clear.
It is said that by the aid of a special “multiplex” device thirty sets of Pollak-Virag apparatus can be used simultaneously on a line! The reader will be able, by the aid of a small calculation, to arrive at some interesting figures as regards their united output.
A common enough sight in any large town is a great sheaf of fine wires running across the streets and over the houses. If you traced their career in one direction you would find that they suddenly terminate, or rather combine into cables, and disappear into the recesses of a house, which is the Telephone Exchange. If you tracked them the other way your experience would be varied enough. Some wires would lead you into public institutions, some into offices, some into snug rooms in private houses. At one time your journey would end in the town, at another you would find yourself roaming far into the country, through green fields and leafy lanes until at last you ran the wire to earth in some large mansion standing in a lordly park. Perhaps you might have to travel hundreds of miles, having struck a “trunk” line connecting two important cities; or you might even be called upon to turn fish and plunge beneath the sea for a while, groping your way along a submarine cable.
In addition to the visible overhead wires that traverse a town there are many led underground through special conduits. And many telephone wires never come out of doors at all, their object being to furnish communication between the rooms of thesame house. The telephone and its friend, the electric-bell, are now a regular part of the equipment of any large premises. The master of the house goes to his telephone when he wishes to address the cook or the steward, or the head-gardener or the coachman. It saves time and labour.
Should he desire to speak to his town-offices he will, unless connected direct, “ring up” the Exchange, into which, as we have seen, flow all the wires of the subscribers to the telephone system of that district. The ringing-up is usually done by rapidly turning a handle which works an electric magnet and rings a bell in the Exchange. The operator there, generally a girl, demands the number of the person with whom the ringer wants to speak, rings up that number, and connects the wires of the two parties.
In some exchanges,e.g.the new Post-Office telephone exchanges, the place of electric-bells is taken by lamps, to the great advantage of the operators, whose ears are thus freed from perpetual jangling. The action of unhooking the telephone receiver at the subscriber’s end sends a current into a relay which closes the circuit of an electric lamp opposite the subscriber’s number in the exchange. Similarly, when the conversation is completed the action of hanging up the receiver again lights another lamp of a different colour, given the exchange warning that the wires are free again.
In America, the country of automatic appliances, the operator is sometimes entirely dispensed with.A subscriber is able, by means of a mechanical contrivance, to put himself in communication with any other subscriber unless that subscriber is engaged, in which case a dial records the fact.
The popularity of the telephone may be judged from the fact that in 1901 the National Telephone Company’s system transmitted over 807 millions of messages, as compared with 89 millions of telegrams sent over the Post Office wires. In America and Germany, however, the telephone is even more universally employed than in England. In the thinly populated prairies of West America the farm-houses are often connected with a central station many miles off, from which they receive news of the outer world and are able to keep in touch with one another. We are not, perhaps, as a nation sufficiently alive to the advantages of an efficient telephone system; and on this account many districts remain telephoneless because sufficient subscribers cannot be found to guarantee use of a system if established. It has been seriously urged that much of our country depopulation might be counteracted by a universal telephone service, which would enable people to live at a distance from the towns and yet be in close contact with them. At present, for the sake of convenience and ease of “getting at” clients and customers, many business men prefer to have their homes just outside the towns where their business is. A cheap and efficient service open to every one would do away with a great deal of travelling that is necessary under existing circumstances,and by making it less important to live near a town allow people to return to the country.
Even Norway has a good telephone system. The telegraph is little used in the more thinly inhabited districts, but the telephone may be found in most unexpected places, in little villages hidden in the recesses of the fiords. Switzerland, another mountainous country, but very go-ahead in all electrical matters, is noted for the cheapness of its telephone services. At Berne or Geneva a subscriber pays £4 the first year, £2, 12s. the second year, and but £1, 12s. the third. Contrast these charges with those of New York, where £15, 10s. to £49, 10s. is levied annually according to service.
The telephone as a public benefactor is seen at its best at Buda-Pesth, the twin-capital of Hungary. In 1893, one Herr Theodore Buschgasch founded in that city a “newspaper”—if so it may be called—worked entirely on the telephone. The publishing office was a telephone exchange; the wires and instruments took the place of printed matter. The subscribers were to be informed entirely by ear of the news of the day.
TheTelefon Hirmondoor “Telephonic Newsteller,” as the “paper” was named, has more than six thousand subscribers, who enjoy their telephones for the very small payment of eighteen florins, or about a penny a day, for twelve hours a day.
News is collected at the central office in the usual journalistic way by telephone, telegraph, and reporters.It is printed by lithography on strips of paper six inches wide and two feet long. These strips are handed to “stentors,” or men with powerful and trained voices, who read the contents to transmitting instruments in the offices, whence it flies in all directions to the ears of the subscribers.
These last know exactly when to listen and what description of information they will hear, for each has over his receiver a programme which is rigidly adhered to. It must be explained at once that theTelefon Hirmondois more than a mere newspaper, for it adds to its practical use as a first-class journal that of entertainer, lecturer, preacher, actor, political speaker, musician. TheTelefonoffices are connected by wire with the theatres, churches, and public halls, drawing from them by means of special receivers the sounds that are going on there, and transmitting them again over the wires to the thousands of subscribers. The Buda-Pesthian has therefore only to consult his programme to see when he will be in touch with his favourite actor or preacher. The ladies know just when to expect the latest hints about the fashions of the day. Nor are the children forgotten, for a special period is set aside weekly for their entertainment in the shape of lectures or concerts.
The advertising fiend, too, must have his say, though he pays dearly for it. On payment of a florin the stentors will shout the virtues of his wares for a space of twelve seconds. The advertising periods are sandwiched in between items of news, so that thesubscriber is bound to hear the advertisements unless he is willing to risk missing some of the news if he hangs up his receiver until the “puff” is finished.
Thanks to theTelefon Hirmondothe preacher, actor, or singer is obliged to calculate his popularity less by the condition of the seats in front of him than by the number of telephones in use while he is performing his part. On the other hand, the subscriber is spared a vast amount of walking, waiting, cab-hire, and expense generally. In fact, if the principle is much further developed, we shall begin to doubt whether a Buda-Pesthian will be able to discover reasons for getting out of bed at all if the receiver hanging within reach of his hand is the entrance to so many places of delight. Will he become a very lazy person; and what will be the effect on his entertainers when they find themselves facing benches that are used less every day? Will the sight of a row of telephone trumpets rouse the future Liddon, Patti, Irving, or Gladstone to excel themselves? It seems rather doubtful. Telephones cannot look interested or applaud.
What is inside the simple-looking receiver that hangs on the wall beside a small mahogany case, or rests horizontally on a couple of crooks over the case? In the older type of instrument the transmitter and receiver are separate, the former fixed in front of the case, the latter, of course, movable so that it can be applied to the ear. But improved patterns have transmitter and receiver in a single movable handle,so shaped that the earpiece is by the ear while the mouthpiece curves round opposite the mouth. By pressing a small lever with the fingers the one or the other is brought into action when required.
The construction of the instrument, of which we are at first a little afraid, and with which we later on learn to become rather angry, is in its general lines simple enough. The first practical telephone, constructed in 1876 by Graham Bell, a Scotchman, consisted of a long wooden or ebonite handle down the centre of which ran a permanent bar-magnet, having at one end a small coil of fine insulated wire wound about it The ends of the wire coil are led through the handles to two terminals for connection with the line wires. At a very short distance from the wire-wound pole of the magnet is firmly fixed by its edges a thin circular iron plate, covered by a funnel-shaped mouthpiece.
The iron plate is, when at rest, concave, its centre being attracted towards the pole of the magnet. When any one speaks into the mouthpiece the sound waves agitate the diaphragm (or plate), causing its centre to move inwards and outwards. The movements of the diaphragm affect the magnetism of the magnet, sometimes strengthening it, sometimes weakening it, and consequently exciting electric currents of varying strength in the wire coil. These currents passing through the line wires to a similar telephone excite the coil in it, and in turn affect the magnetism of the distant magnet, which attractsor releases the diaphragm near its pole, causing undulations of the air exactly resembling those set up by the speaker’s words. To render the telephone powerful enough to make conversation possible over long distances it was found advisable to substitute for the one telephone a special transmitter, and to insert in the circuit a battery giving a much stronger current than could possibly be excited by the magnet in the telephone at the speaker’s end.
Edison in 1877 invented a special transmitter made of carbon. He discovered that the harder two faces of carbon are pressed together the more readily will they allow current to pass; the reason probably being that the points of contact increase in number and afford more bridges for the current.
Accordingly his transmitter contains a small disc of lampblack (a form of carbon) connected to the diaphragm, and another carbon or platinum disc against which the first is driven with varying force by the vibrations of the voice.
The Edison transmitter is therefore in idea only a modification of the microphone. It acts as aregulatorof current, in distinction to the Bell telephone, which is only anexciterof current. Modern forms of telephones unite the Edison transmitter with the Bell receiver.
The latter is extremely sensitive to electric currents, detecting them even when of the minutest power. We have seen that Marconi used a telephone in his famous transatlantic experiments to distinguish thesignals sent from Cornwall. A telephone may be used with an “earth return” instead of a second wire; but as this exposes it to stray currents by induction from other wires carried on the same poles or from the earth itself, it is now usual to use two wires, completing the metallic circuit. Even so a subscriber is liable to overhear conversations on wires neighbouring his own; the writer has lively recollections of first receiving news of the relief of Ladysmith in this manner.
Owing to the self-induction of wires in submarine cables and the consequent difficulty of forcing currents through them, the telephone is at present not used in connection with submarine lines of more than a very moderate length. England has, however, been connected with France by a telephone cable from St. Margaret’s Bay to Sangatte, 23 miles; and Scotland with Ireland, Stranraer to Donaghadee, 26 miles. The former cable enables speech between London and Marseilles, a distance of 900 miles; and the latter makes it possible to speak from London to DublinviâGlasgow. The longest direct line in existence is that between New York and Chicago, the complete circuit of which uses 1900 miles of stout copper wire, raised above the ground on poles 35 feet high.
The efficiency of the telephone on a well laid system is so great that it makes very little difference whether the persons talking with one another are 50 or 500 miles apart. There is no reason why aCape-to-Cairo telephone should not put the two extremities of Africa in clear vocal communication. We may even live to see the day when a London business man will be able to talk with his agent in Sydney, Melbourne, or Wellington.
A step towards this last achievement has been taken by M. Germain, a French electrician, who has patented a telephone which can be used with stronger currents than are possible in ordinary telephones; thereby, of course, increasing the range of speech on submarine cables.
The telephone that we generally use has a transmitter which permits but a small portion of the battery power to pass into the wires, owing to the resistance of the carbon diaphragm. The weakness of the current is to a great extent compensated by the exceedingly delicate nature of the receiver.
M. Germain has reversed the conditions with a transmitter that allows a very high percentage of the current to flow into the wires, and a comparatively insensitive receiver. The result is a “loud-speaking telephone”—not a novelty, for Edison invented one as long ago as 1877—which is capable of reproducing speech in a wonderfully powerful fashion.
M. Germain, with the help of special tubular receivers, has actually sent messages through a line having the same resistance as that of the London-Paris line, so audibly that the words could be heard fifteen yards from the receiver in the open air!
In days when wireless telegraphy is occupying such a great deal of the world’s attention, it is not likely to cause much astonishment in the reader to learn that wireless transmission ofspeechover considerable distances is an accomplished fact. We have already mentioned (see “Wireless Telegraphy”) that by means of parallel systems of wires Sir William Preece bridged a large air-gap, and induced in the one sounds imparted to the other.
Since then two other methods have been introduced; and as a preface to the mention of the first we may say a few words about Graham Bell’sPhotophone.
In this instrumentlightis made to do the work of a metal connection between speaker and listener. Professor Bell, in arranging the Photophone, used a mouthpiece as in his electric telephone, but instead of a diaphragm working in front of a magnet to set up electric impulses along a wire he employed a mirror of very thin glass, silvered on one side. The effect of sound on this mirror was to cause rapid alterations of its shape from concave to convex, and consequent variations of its reflecting power. A strong beam of light was concentrated on the centre of the mirror through a lens, and reflected by the mirror at an angle through another lens in the direction of the receiving instrument. The receiver consisted of a parabolic reflector to catch the raysand focus them on a selenium cell connected by an electric circuit with an ordinary telephone earpiece.
On delivering a message into the mouthpiece the speaker would, by agitating the mirror, send a succession of light waves of varying intensity towards the distant selenium cell. Selenium has the peculiar property of offering less resistance to electrical currents when light is thrown upon it than when it is in darkness: and the more intense is the light the less is the obstruction it affords. The light-waves from the mirror, therefore, constantly alter its capacity as a conductor, allowing currents to pass through the telephone with varying power.
In this way Professor Bell bridged 800 yards of space; over which he sent, besides articulate words, musical notes, using for the latter purpose a revolving perforated disc to interrupt a constant beam of light a certain number of times per second. As the speed of the disc increased the rate of the light-flashes increased also, and produced in the selenium cell the same number of passages to the electric current, converted into a musical note by the receiver. So that by means of mechanical apparatus a “playful sunbeam” could literally be compelled to play a tune.
From the Photophone we pass to another method of sound transmission by light, with which is connected the name of Mr. Hammond V. Hayes of Boston, Massachusetts. It is embodied in the Radiophone, or the Ray-speaker, for it makes strong rays of light carry the human voice.
Luminous bodies give off heat. As the light increases, so as a general rule does the heat also. At present we are unable to create strong light without having recourse to heat to help us, since we do not know how to cause other vibrations of sufficient rapidity to yield the sensation of light. But we can produce heat directly, and heat will set atoms in motion, and the ether too, giving us light, but taking as reward a great deal of the energy exerted. Now, the electric arc of a searchlight produces a large amount of lightandheat. The light is felt by the eye at a distance of many miles, but the body is not sensitive enough to be aware of the heat emanating from the same source. Mr. Hayes has, however, found the heat accompanying a searchlight beam quite sufficient to affect a mechanical “nerve” in a far-away telephone receiver.
The transmitting apparatus is a searchlight, through the back of which run four pairs of wires connected with a telephone mouthpiece after passing through a switch and resistance-box or regulator. The receiver is a concave mirror, in the focus of which is a tapering glass bulb, half filled with carbonised filament very sensitive to heat. The tapering end of the bulb projects through the back of the mirror into an ear tube.
If a message is to be transmitted the would-be speaker turns his searchlight in the direction of the person with whom he wishes to converse, and makes the proper signals. On seeing them the other presents his mirror to the beam and listens.
The speaker’s voice takes control of the searchlight beam. The louder the sound the more brilliantly glows the electric arc; the stronger becomes the beam, the greater is the amount of heat passed on to the mirror and gathered on the sensitive bulb. The filament inside expands. The tapering point communicates the fact to the earpiece.
This operation being repeated many times a second the earpiece fills with sound, in which all the modulations of the far-distant voice are easily distinguishable.
Two sets of the apparatus above described are necessary for a conversation, the functions of the searchlight and the bulb not being reversible. But inasmuch as all large steamers carry searchlights the necessary installation may be completed at a small expense. Mr. Hayes’ invention promises to be a rival to wireless telegraphy over comparatively short distances. It can be relied upon in all weathers, and is a fast method of communication. Like the photophone it illustrates the inter-relationship of the phenomena of Sound, Light, and Heat, and the readiness with which they may be combined to attain an end.
Next we turn from air to earth, and to the consideration of the work of Mr. A. F. Collins of Philadelphia. This electrician merely makes use of the currents flowing in all directions through the earth, and those excited by an electric battery connected with earth. The outfit requisite for sending wireless spoken messages consists of a couple of convenientstands, as many storage batteries, sets of coils, and receiving and transmitting instruments.
The action of the transmitter is to send from the battery a series of currents through the coils, which transmit them, greatly intensified, to the earth by means of a wire connected with a buried wire-screen. The electric disturbances set up in the earth travel in all directions, and strike a similar screen buried beneath the receiving instrument, where the currents affect the delicate diaphragm of the telephone earpiece.
The system is, in fact, upon all fours with Mr. Marconi’s, the distinguishing feature being that the ether of the atmosphere is used in the latter case, that of the earth in the former. The intensity coils are common to both; the buried screens are the counterpart of the aërial kites or balloons; the telephone transmitter corresponds to the telegraphic transmitting key; the earpiece to the coherer and relay. No doubt in time Mr. Collins will “tune” his instruments, so obtaining below ground the same sympathetic electric vibrations which Mr. Marconi, Professor Lodge, or others have employed to clothe their aërial messages in secrecy.
Even if Thomas Edison had not done wonders with electric lighting, telephones, electric torpedoes, new processes for separating iron from its ore, telegraphy, animated photography, and other things too numerous to mention, he would still have made for himself an enduring name as the inventor of the Phonograph. He has fitly been called the “Wizard of the West” from his genius for conjuring up out of what would appear to the multitude most unpromising materials startling scientific marvels, among which none is more truly wizard-like than the instrument that is as receptive of sound as the human ear, and of illimitable reproducing power. By virtue of its elfishly human characteristic, articulate speech, it occupies, and always will occupy, a very high position as a mechanical wonder. When listening to a telephone we are aware of the fact that the sounds are immediate reproductions of a living person’s voice, speaking at the moment and at a definite distance from us; but the phonographic utterances are those of a voice perhaps stilled for ever, and the difference adds romance to the speaking machine.
The Phonograph was born in 1876. As we may imagine, its appearance created a stir. A contributorto theTimeswrote in 1877: “Not many weeks have passed since we were startled by the announcement that we could converse audibly with each other, although hundreds of miles apart, by means of so many miles of wire with a little electric magnet at each end.
“Another wonder is now promised us—an invention purely mechanical in its nature, by means of which words spoken by the human voice can be, so to speak, stored up and reproduced at will over and over again hundreds, it may be thousands, of times. What will be thought of a piece of mechanism by means of which a message of any length can be spoken on to a plate of metal—that plate sent by post to any part of the world and the message absolutely respoken in the very voice of the sender, purely by mechanical agency? What, too, shall be said of a mere machine, by means of which the old familiar voice of one who is no longer with us on earth can be heard speaking to us in the very tones and measure to which our ears were once accustomed?”
The first Edison machine was the climax of research in the realm of sound. As long ago as 1856 a Mr. Leo Scott made an instrument which received the formidable name of Phonautograph, on account of its capacity to register mechanically the vibrations set up in the atmosphere by the human voice or by musical instruments. A large metal cone like the mouth of an ear-trumpet had stretched across its smaller end a membrane, to which was attached a very delicatetracing-point working on the surface of a revolving cylinder covered with blackened paper. Any sound entering the trumpet agitated the membrane, which in turn moved the stylus and produced a line on the cylinder corresponding to the vibration. Scott’s apparatus could only record. It was, so to speak, the first half of the phonograph. Edison, twenty years later, added the active half. His machine, as briefly described in theTimes, was simple; so very simple that many scientists must have wondered how they failed to invent it themselves.
A metal cylinder grooved with a continuous square-section thread of many turns to the inch was mounted horizontally on a long axle cut at one end with a screw-thread of the same “pitch” as that on the cylinder. The axle, working in upright supports, and furnished with a heavy flywheel to render the rate of revolution fairly uniform, was turned by a handle. Over the grooved cylinder was stretched a thin sheet of tinfoil, and on this rested lightly a steel tracing-point, mounted at the end of a spring and separated from a vibrating diaphragm by a small pad of rubber tubing. A large mouthpiece to concentrate sound on to the diaphragm completed the apparatus.
To make a record with this machine the cylinder was moved along until the tracing-point touched one extremity of the foil. The person speaking into the mouthpiece turned the handle to bring a fresh surface of foil continuously under the point, which, owing to the thread on the axle and the groove on thecylinder being of the same pitch, was always over the groove, and burnished the foil down into it to a greater or less depth according to the strength of the impulses received from the diaphragm.
A unique group of Phonographs. 1. The oldest phonograph in existence, now in South Kensington Museum. 2. Tinfoil instrument. 3. A cheaper form of the same. 4. A “spectacle-form” graphophone. 5. An exactly similar instrument, half-size scale. 6. A doll fitted with phonograph.
A unique group of Phonographs. 1. The oldest phonograph in existence, now in South Kensington Museum. 2. Tinfoil instrument. 3. A cheaper form of the same. 4. A “spectacle-form” graphophone. 5. An exactly similar instrument, half-size scale. 6. A doll fitted with phonograph.
The record being finished, the point was lifted off the foil, the cylinder turned back to its original position, and the point allowed to run again over the depressions it had made in the metal sheet. The latter now became the active part, imparting to the air by means of the diaphragm vibrations similar in duration and quality to those that affected it when the record was being made.
It is interesting to notice that the phonograph principle was originally employed by Edison as a telephone “relay.” His attention had been drawn to the telephone recently produced by Graham Bell, and to the evil effects of current leakage in long lines. He saw that the amount of current wasted increased out of proportion to the length of the lines—even more than in the proportion of the squares of their lengths—and he hoped that a great saving of current would be effected if a long line were divided into sections and the sound vibrations were passed from one to the other by mechanical means. He used as the connecting link between two sections a strip of moistened paper, which a needle, attached to a receiver, indented with minute depressions, that handed on the message to another telephone. The phonograph proper, as a recording machine, was an after-thought.
Edison’s first apparatus, besides being heavy andclumsy, had in practice faults which made it fall short of the description given in theTimes. Its tone was harsh. The records, so far from enduring a thousand repetitions, were worn out by a dozen. To these defects must be added a considerable difficulty in adjusting a record made on one machine to the cylinder of another machine.
Edison, being busy with his telephone and electric lamp work, put aside the phonograph for a time. Graham Bell, his brother, Chichester Bell, and Charles Sumner Tainter, developed and improved his crude ideas. They introduced the Graphophone, using easily removable cylinder records. For the tinfoil was substituted a thin coating of a special wax preparation on light paper cylinders. Clockwork-driven motors replaced the hand motion, and the new machines were altogether more handy and effective. As soon as he had time Edison again entered the field. He conceived the solid wax cylinder, and patented a small shaving apparatus by means of which a record could be pared away and a fresh surface be presented for a new record.
The phonograph or graphophone of to-day is a familiar enough sight; but inasmuch as our readers may be less intimately acquainted with its construction and action than with its effects, a few words will now be added about its most striking features.
In the first place, the record remains stationary while the trumpet, diaphragm and stylus pass over it. The reverse was the case with the tinfoil instrument.
The record is cut by means of a tiny sapphire point having a circular concave end very sharp at the edges, to gouge minute depressions into the wax. The point is agitated by a delicate combination of weights and levers connecting it with a diaphragm of French glass 1/140 inch thick. The reproducing point is a sapphire ball of a diameter equal to that of the gouge. It passes over the depressions, falling into them in turn and communicating its movements to a diaphragm, and so tenderly does it treat the records that a hundred repetitions do not inflict noticeable damage.
It is a curious instance of the manner in which man unconsciously copies nature that the parts of the reproducing attachment of a phonograph contains parts corresponding in function exactly to those bones of the ear known as the Hammer, Anvil, and Stirrup.
To understand the inner working of the phonograph the reader must be acquainted with the theory of sound. All sound is the result of impulses transmitted by a moving body usually reaching the ear through the medium of the air. The quantity of the sound, or loudness, depends on the violence of the impulse; the tone, or note, on the number of impulses in a given time (usually fixed as one second); and the quality, ortimbre, as musicians say, on the existence of minor vibrations within the main ones.
If we were to examine the surface of a phonograph record (or phonogram) under a powerfulmagnifying glass we should see a series of scoops cut by the gouge in the wax, some longer and deeper than others, long and short, deep and shallow, alternating and recurring in regular groups. The depth, length, and grouping of the cuts decides the nature of the resultant note when the reproducing sapphire point passes over the record—at a rate of about ten inches a second.
The study of a tracing made on properly prepared paper by a point agitated by a diaphragm would enable us to understand easily the cause of that mysterious variation intimbrewhich betrays at once what kind of instrument has emitted a note of known pitch. For instance, let us take middle C, which is the result of a certain number of atmospheric blows per second on the drum of the ear. The same note may come from a piano, a violin, a banjo, a man’s larynx, an organ, or a cornet; but we at once detect its source. It is scarcely imaginable that a piano and a cornet should be mistaken for one another. Now, if the tracing instrument had been at work while the notes were made successively it would have recorded a wavy line, each wave of exactly the samelengthas its fellows, but varying in itsoutlineaccording to the character of the note’s origin. We should notice that the waves were themselves wavy in section, being jagged like the teeth of a saw, and that the small secondary waves differed in size.
The minor waves are the harmonics of the mainnote. Some musical instruments are richer in these harmonics than others. The fact that these delicate variations are recorded as minute indentations in the wax and reproduced is a striking proof of the phonograph’s mechanical perfection.
Furthermore, the phonograph registers not only these composite notes, but also chords or simultaneous combinations of notes, each of which may proceed from a different instrument. In its action it here resembles a man who by constant practice is able to add up the pounds, shillings, and pence columns in his ledger at the same time, one wave system overlapping and blending with another.
The phonograph is not equally sympathetic with all classes of sounds. Banjo duets make good records, but the guitar gives a poor result. Similarly, the cornet is peculiarly effective, but the bass drum disappointing. The deep chest notes of a man come from the trumpet with startling truth, but the top notes on which the soprano prides herself are often sadly “tinny.” The phonograph, therefore, even in its most perfect form is not the equal of the exquisitely sensitive human ear; and this may partially be accounted for by the fact that the diaphragm in both recorder and reproducer has its own fundamental note which is not in harmony with all other notes, whereas the ear, like the eye, adapts itself to any vibration.
Yet the phonograph has an almost limitless répertoire. It can justly be claimed for it that it is many musical instruments rolled into one. It will reproduceclearly and faithfully an orchestra, an instrumental soloist, the words of a singer, a stump orator, or a stage favourite. Consequently we find it every where—at entertainments, in the drawing-room, and even tempting us at the railway station or other places of public resort to part with our superfluous pence. At the London Hippodrome it discourses to audiences of several thousand persons, and in the nursery it delights the possessors of ingeniously-constructed dolls which, on a button being pressed and concealed machinery being brought into action, repeat some well-known childish melody.
It must not be supposed that the phonograph is nothing more than a superior kind of scientific toy. More serious duties than those of mere entertainment have been found for it.
At the last Presidential Election in the States the phonograph was often called upon to harangue large meetings in the interests of the rival candidates, who were perhaps at the time wearing out their voices hundreds of miles away with the same words.
Since the pronunciation of a foreign language is acquired by constant imitation of sounds, the phonograph, instructed by an expert, has been used to repeat words and phrases to a class of students until the difficulties they contain have been thoroughly mastered. The sight of such a class hanging on the lips—or more properly the trumpet—of a phonograph gifted with the true Parisian accent may be common enough in the future.
As a mechanical secretary and substitute for the shorthand writer the phonograph has certainly passed the experimental stage. Its daily use by some of the largest business establishments in the world testify to its value in commercial life. Many firms, especially American, have invested heavily in establishing phonograph establishments to save labour and final expense. The manager, on arriving at his office in the morning, reads his letters, and as the contents of each is mastered, dictates an answer to a phonograph cylinder which is presently removed to the typewriting room, where an assistant, placing it upon her phonograph and fixing the tubes to her ears, types what is required. It is interesting to learn that at Ottawa, the seat of the Canadian Government, phonographs are used for reporting the parliamentary proceedings and debates.
There is therefore a prospect that, though the talking-machine may lose its novelty as an entertainer, its practical usefulness will be largely increased. And while considering the future of the instrument, the thought suggests itself whether we shall be taking full advantage of Mr. Edison’s notable invention if we neglect to make records of all kinds of intelligible sounds which have more than a passing interest. If the records were made in an imperishable substance they might remain effective for centuries, due care being taken of them in special depositories owned by the nation. To understand what their value would be to future generations we have only to imagine ourselves listening to the long-stilled thunder of EarlChatham, to the golden eloquence of Burke, or the passionate declamations of Mrs. Siddons. And in the narrower circle of family interests how valuable a part of family heirlooms would be the phonograms containing a vocal message to posterity from Grandfather this, or Great-aunt that, whose portraits in the drawing-room album do little more than call attention to the changes in dress since the time when their subjects faced the camera!
Record-Making and Manufacture.—Phonographic records are of two shapes, the cylindrical and the flat, the latter cut with a volute groove continuously diminishing in diameter from the circumference to the centre. Flat records are used in the Gramophone—a reproducing machine only. Their manufacture is effected by first of all making a record on a sheet of zinc coated with a very thin film of wax, from which the sharp steel point moved by the recording diaphragm removes small portions, baring the zinc underneath. The plate is then flooded with an acid solution, which eats into the bared patches, but does not affect the parts still covered with wax. The etching complete, the wax is removed entirely, and a cast or electrotypenegativerecord made from the zinc plate. The indentations of the original are in this represented by excrescences of like size; and when the negative block is pressed hard down on to a properly prepared disc of vulcanite or celluloid, the latter is indented in a manner that reproduces exactly the tones received on the “master” record.
Cylindrical records are made in two ways, by moulding or by copying. The second process is extremely simple. The “master” cylinder is placed on a machine which also rotates a blank cylinder at a short distance from and parallel to the first. Over the “master” record passes a reproducing point, which is connected by delicate levers to a cutting point resting on the “blank,” so that every movement of the one produces a corresponding movement of the other.
This method, though accurate in its results, is comparatively slow. Themouldingprocess is therefore becoming the more general of the two. Edison has recently introduced a most beautiful process for obtaining negative moulds from wax positives. Owing to its shape, a zinc cylinder could not be treated like a flat disc, as, the negative made, it could not be detached without cutting. Edison, therefore, with characteristic perseverance, sought a way of electrotyping the wax, which, being a non-conductor of electricity, would not receive a deposit of metal. The problem was how to deposit on it.
Any one who has seen a Crookes’ tube such as is used for X-ray work may have noticed on the glass a black deposit which arises from the flinging off from the negative pole of minute particles of platinum. Edison took advantage of this repellent action; and by enclosing his wax records in a vacuum between two gold poles was able to coat them with an infinitesimally thin skin of pure gold, on which silveror nickel could be easily deposited. The deposit being sufficiently thick the wax was melted out and the surface of the electrotype carefully cleaned. To make castings it was necessary only to pour in wax, which on cooling would shrink sufficiently to be withdrawn. The delicacy of the process may be deduced from the fact that some of the sibilants, or hissing sounds of the voice, are computed to be represented by depressions less than a millionth of an inch in depth, and yet they are most distinctly reproduced! Cylinder records are made in two sizes, 2-1/2 and 5 inches in diameter respectively. The larger size gives the most satisfactory renderings, as the indentations are on a larger scale and therefore less worn by the reproducing point. One hundred turns to the inch is the standard pitch of the thread; but in some records the number is doubled.
Phonographs, Graphophones, and Gramophones are manufactured almost entirely in America, where large factories, equipped with most perfect plant and tools, work day and night to cope with the orders that flow in freely from all sides. One factory alone turns out a thousand machines a day, ranging in value from a few shillings to forty pounds each. Records are made in England on a large scale; and now that the Edison-Bell firm has introduced the unbreakable celluloid form their price will decrease. By means of the Edison electrotyping process a customer can change his record without changing his cylinder. He takes the cylinder to the factory, where it is heated,placed in the mould, and subjected to great pressure which drives the soft celluloid into the mould depressions; and behold! in a few moments “Auld Lang Syne” has become “Home, Sweet Home,” or whatever air is desired. Thus altering records is very little more difficult than getting a fresh book at the circulating library.
This instrument is a phonograph working entirely by means of light and electricity.
The flame of an electric lamp is brought under the influence of sound vibrations which cause its brilliancy to vary at every alteration of pitch or quality.
The light of the flame is concentrated through a lens on to a travelling photographic sensitive film, which, on development in the ordinary way, is found to be covered with dark and bright stripes proportionate in tone to the strength of the light at different moments. The film is then passed between a lamp and a selenium plate connected with an electric circuit and a telephone. The resistance of the selenium to the current varies according to the power of the light thrown upon it. When a dark portion of the film intercepts the light of the lamp the selenium plate offers high resistance; when the light finds its way through a clear part of the film the resistance weakens. Thus the telephone is submitted to a series of changes affecting the “receiver.” As in the makingof the record speech-vibrations affect light, and the light affects a sensitive film; so in its reproduction the film affects a sensitive selenium plate, giving back to a telephone exactly what it received from the sound vibrations.
One great advantage of Mr. Ruhmer’s method is that from a single film any number of records can be printed by photography; another, that, as with the Telegraphone (see below), the same film passed before a series of lamps successively is able to operate a corresponding number of telephones.
The inventor is not content with his success. He hopes to record not merely sounds but even pictures by means of light and a selenium plate.
Having dealt with the phonograph and the telephone separately, we may briefly consider one or two ingenious combinations of the two instruments. The word Telephonograph signifies an apparatus for recording sounds sent from a distance. It takes the place of the human listener at the telephone receiver.
Let us suppose that a Reading subscriber wishes to converse along the wires with a friend in London, but that on ringing up his number he discovers that the friend is absent from his home or office. He is left with the alternative of either waiting till his friend returns, which may cause a serious loss of time, or of dictating his message, a slow and laborious process. This withthe ordinary telephonic apparatus. But if the London friend be the possessor of a Telephonograph, the person answering the call-bell can, if desired to do so, switch the wires into connection with it and start the machinery; and in a very short time the message will be stored up for reproduction when the absent friend returns.
The Telephonograph is the invention of Mr. J. E. O. Kumberg. The message is spoken into the telephone transmitter in the ordinary way, and the vibrations set up by the voice are caused to act upon a recording stylus by the impact of the sound waves at the further end of the wires. In this manner a phonogram is produced on the wax cylinder in the house or office of the person addressed, and it may be read off at leisure. A very sensitive transmitter is employed, and if desired the apparatus can be so arranged that by means of a double-channel tube the words spoken are simultaneously conveyed to the telephone and to an ordinary phonograph, which insures that a record shall be kept of any message sent.
TheTelegraphone, produced by Mr. Valdemar Poulsen, performs the same functions as the telephonograph, but differs from it in being entirely electrical. It contains no waxen cylinder, no cutting-point; their places are taken respectively by a steel wire wound on a cylindrical drum (each turn carefully insulated from its neighbours) and by a very small electro-magnet, which has two delicate points that pass along the wire, one on either side, resting lightly upon it.
As the drum rotates, the whole of the wire passes gradually between the two points, into which a series of electric shocks is sent by the action of the speaker’s voice at the further end of the wires. The shocks magnetise the portion of steel wire which acts as a temporary bridge between the two points. At the close of three and a half minutes the magnet has worked from one end of the wire coil to the other; it is then automatically lifted and carried back to the starting-point in readiness for reproduction of the sounds. This is accomplished by disconnecting the telegraphone from the telephone wires and switching it on to an ordinary telephonic earpiece or receiver. As soon as the cylinder commences to revolve a second time, the magnet is influenced by the series of magnetic “fields” in the wires, and as often as it touches a magnetised spot imparts an impulse to the diaphragm of the receiver, which vibrates at the rate and with the same force as the vibrations originally set up in the distant transmitter. The result is a clear and accurate reproduction of the message, even though hours and even days may have elapsed since its arrival.
As the magnetic effects on the wire coil retain their power for a considerable period, the message may be reproduced many times. As soon as the wire-covered drum is required for fresh impressions, the old one is wiped out by passing a permanent magnet along the wire to neutralise the magnetism of the last message.
Mr. Poulsen has made an instrument of a different type to be employed for the reception of an unusually lengthy communication. Instead of a wire coil on a cylinder, a ribbon of very thin flat steel spring is wound from one reel on to another across the poles oftwoelectro-magnets, which touch the lower side only of the strip. The first magnet is traversed by a continuous current to efface the previous record; the second magnetises the strip in obedience to impulses from the telephone wires. The message complete, the strip is run back, and the magnets connected with receivers, which give out loud and intelligent speech as the strip again traverses them. The Poulsen machine makes the transmission of the same message simultaneously through several telephones an easy matter, as the strip can be passed over a series of electro-magnets each connected with a telephone.