Chapter M: J. Luvini, in an article inserted in ‘Les Mondes,’ March 7, (5)

An articulating telephone is not necessary in order to obtain simultaneous transmission: the musical telephones devised by MM. Petrina, Gray, Froment, &c., are quite sufficient, and a brief explanation of their principle will make this intelligible. Suppose that there are seven electro-magnetic vibrators at the two corresponding stations, which are tuned with the same tuning-fork on the different notes of the scale, and suppose that a key-board, resembling the Morse telegraph key, is arranged so that, by lowering the keys, electric reaction takes place on each vibrator: it is easy to see that these vibrators may be made to react in the same way on the corresponding vibrators of the opposite station; but they must be tuned on the same note, and the sounds emitted will continue while the keys are lowered. By keeping them down for a shorter or longer time, the long or short sounds which constitute the elements of telegraphic language in the Morse system may be obtained, and consequently an audible transmission becomes possible. Let us now suppose that a telegraphist accustomed to this mode of transmission is placed before each of the vibrators, and that they transmit different messages at the same moment in this way: the telegraphic wire will be instantaneously traversed by seven currents, broken and massed upon each other, and they might be expected to produce a medley of confused sounds on the vibrators at the receiving station; but since they each harmonise with the corresponding vibrator, they have no sensible influence except on those for which they are intended. The dominant sound may be made still more distinct by applying a Helmholtz resonator to each vibrator,[18] that is, an acoustic instrument which will only vibrate under the influence of the note to which it is tuned. In this way it is possible to select the transmitted sounds, and only to allow each _employé_ to hear that which is intended for him. Consequently, however confused the sounds may be on the receiving vibrators, the person to whom _do_ is assigned will only receive _do_ sounds, the person to whom _sol_ is assigned will only receive _sol_ sounds, so that correspondence may be carried on as well as if they had each a special wire.

In the mode we have described, this telegraphic system only admits of audible transmissions, and consequently cannot register messages. To supply this defect, it has been suggested to make the receiving vibrators react on registers, so arranging the latter that their electric organ may present such magnetic inertia, that, when it is influenced by the vibrations of sound, its effect may be maintained throughout the time of vibration. Experiments show that a Morse receiver, worked by the current of a local battery, will be enough for this purpose; so that if the musical vibrator is made to react as a relay, that is, on a contact in connection with the local battery and the receiver, the dots and dashes may be obtained on it which are the constituent elements of the Morse code.

On these principles, and considering that the musical spaces separating the different notes of the scale are such as may be easily distinguished by the resonator, seven simultaneous transmissions may be obtained on the same wire; but experience shows that it is necessary to be content with a much smaller number. Yet this number may easily be doubled by applying the mode of transmission in an opposite direction to the system.

Mr. Bell states that the idea of applying the telephone to multiple electric transmissions occurred simultaneously to M. Paul Lacour of Copenhagen, to Mr. Elisha Gray of Chicago, to Mr. Varley of London, and to Mr. Edison of New York; but there is some confusion here, for we have already seen, from reference to the patents, that Mr. Varley’s system dates from 1870, that of M. Paul Lacour from September 1874, that of Mr. Elisha Gray from February 1875, and those of Messrs. Bell and Edison were still later. Yet it appears from Mr. Gray’s specification that he was the first to conceive and execute instruments of the kind. In fact, in a specification drawn up on August 6, 1874, he distinctly put forward the system we have described, and which is the basis of those of which we have still to speak. This specification was only an addition to two others made out in April and June 1874. Mr. Varley’s system has only an indirect relation to the one we have described. It appears from what Mr. Bell said on the subject in a paper addressed to the Society of Telegraphic Engineers in London, that he himself only attaches a secondary interest to this invention.

He said that he had been struck with the idea that the greater or less duration of a musical sound might represent the dot and dash of the telegraphic alphabet, and it occurred to him that simultaneous telegraphic transmissions, of which the number should only be limited by the delicacy of the sense of hearing, might be obtained by suitable combinations of long and short sounds, and that these should be effected by a keyboard of tuning-forks applied to one end of a telegraphic line, and so arranged as to react electrically on electro-magnetic instruments striking on the strings of a piano. For this purpose it would be necessary to assign an employé to each of the keys for the service of transmission, and to arrange that his correspondent should only distinguish his peculiar note among all those transmitted. It was this idea, Mr. Bell adds, which led to his researches in telephony.

For several years he sought for the best mode of reproducing musical sounds at a distance by means of vibrating rheotomes: the best results were given by a steel plate vibrating between two contacts, of which the vibrations were electrically produced and maintained by an electro-magnet and a local battery. In consequence of its vibration, the two contacts were touched alternately, and the two circuits were alternately broken; the local circuit which kept the plate in vibration, and the other which was connected with the line, and reacted on the distant receiver, so as to effect simultaneous vibrations in it. A Morse key was placed in the latter circuit near the sending instrument, and when it was lowered, vibrations were sent through the line; when it was raised, these vibrations ceased, and it is easy to see that, by lowering the key for a longer or shorter time, the short and long sounds necessary for the different combinations of telegraphic language could be obtained. Moreover, if the vibrating plate of the receiving instrument were so regulated as to vibrate in unison with the sending instrument in correspondence, it would vibrate better with this sender than with another whose plate was not so adjusted.

It is evident that different sounds might be simultaneously transmitted with several plates by this arrangement of contact breaker, and that at the receiving station the sounds might be distinguished by each employé, since the one which corresponds to the fundamental note of each vibrating plate is reproduced by that plate. Consequently, the sounds produced by the vibrating plate of _do_, for example, will only be audible at the receiving station on the plate tuned to _do_, and the same will be the case with the other plates; so that the sounds will reach their destination, if not without confusion, yet with sufficient clearness to be distinguished by the employés.

Mr. Bell sums up the defects still existing in his system as follows:--1st. The receiver of the messages must have a good musical ear, in order to distinguish the value of sounds. 2nd. Since the signals can only take place when the transmitted currents are in the same direction, two wires must be employed in order to exchange messages on each side.

He surmounted the first difficulty by providing the receiver with an instrument which he called the vibrating contact breaker, and which registered automatically the sounds produced. This contact breaker was placed in the circuit of a local battery, which could work a Morse instrument under certain conditions. When the sounds emitted by the instrument did not correspond with those for which it had been tuned, the contact breaker had no effect on the telegraphic instrument: it only acted when the sounds were those which were to be interpreted, and its action necessarily corresponded to the length of the sounds.

Mr. Bell adds that he applied the system to electro-chemical telegraphs; but we need not dwell on this part of the invention, since, as we have said, it is no longer his special study.

_System of M. Lacour of Copenhagen._--M. Lacour’s system was patented on the 2nd September, 1874, but his experiments were commenced on the 5th June of the same year. Since M. Lacour believed that the vibrations would be imperceptible on long lines, his first attempts were made on a somewhat short line; but in November 1874 fresh experiments were made between Fredericia and Copenhagen on a line 225 miles in length, and it was ascertained that vibratory effects could be easily transmitted, even under the influence of a rather weak battery.

In M. Lacour’s system, the sending instrument is a simple tuning-fork, placed in a horizontal position, and one of its arms reacts on a contact breaker, which can produce precisely the same number of discharges of currents as there are vibrations of the tuning-fork. If a Morse manipulator is inserted in the circuit, it is evident that if it is worked so as to produce the dots and dashes of the Morse alphabet, the same signals will be reproduced at the opposite station, and the signals will be manifested by long and short sounds, if an electro-magnetic receiver is connected with the circuit. This sender is shown fig. 59.

Fig. 60 represents M. Lacour’s receiver. It consists of a tuning-fork F made of soft iron, not of steel like the sending tuning-fork, and each of its branches is inserted in the bobbin of an electro-magnetic coil C C; two distinct electro-magnets M M react close to the extremities of the fork, in such a way that the polarities developed on the two branches of the fork under the influence of the coils C C should be of contrary signs to those of the electro-magnets M M.

If this double electro-magnetic system is inserted in a line circuit, it follows that, for each discharge of the transmitted current, a corresponding attraction of the branches of the tuning-fork will take place, and consequently there will be a vibration, producing a sound, if the discharges are numerous. This sound will naturally be short or long in proportion to the duration of the sender’s action, and it will be the same as that of the tuning-fork in that instrument. Again, if one branch of the tuning-fork reacts on a contact P inserted in the circuit of the local battery communicating with a Morse receiver, traces will be produced on this receiver of length varying with the duration of the sounds, for the Morse electro-magnet will be so quickly affected by the successive breaks in the current that its armature will remain stationary throughout each vibration. ‘I have not yet been able,’ said M. Lacour in an address delivered before the Danish Academy of Science in 1875, ‘to calculate the time necessary for the production of definite vibrations in the tuning-fork. Different factors have to be considered, but experiment has shown that the time which elapses before the local circuit is broken is such a small fraction of a second as to be almost inappreciable, even when the current is very weak.

‘Since intermittent currents only affect a tuning-fork on condition that it vibrates in unison with the one which produces them, it follows that if a series of sending tuning-forks, tuned to the different notes of the scale, is placed at one end of a circuit, and if a similar series of electro-magnetic tuning-forks, in exact accordance with the first, is placed at the other end of the circuit, the intermittent currents transmitted by the sending tuning-forks will be added to each other without becoming confused, and each of the receiving tuning-forks will only be affected by the currents emitted by the tuning-fork in unison with it. In this way the combinations of elementary signals representing a word may be telegraphed simultaneously.’

M. Lacour enumerates the ways in which this system may be applied as follows: ‘If the keys in connection with the sending tuning-forks are placed side by side, and are lowered in succession, or two or three together, it will be enough to play on the keys as on a musical instrument, in order that the air may be heard at the receiving station, or the signals transmitted simultaneously may each belong to a different message. This system will therefore allow the furthest station on a line to communicate with one or several intermediate stations, and _vice versa_, without disturbing the communication at other stations. In this way two stations can exchange signals, unperceived by the rest. The power of sending many signals at once affords a good means of improving the autographic telegraph. In the instruments now in use, such as those of Caselli and D’Arlincourt, there is only one tracing stylus, and this stylus must pass over the whole surface of the telegram in order to obtain a copy of it, but with the telephone a certain number of styli may be placed side by side in the form of a comb, and this comb need only be drawn in a certain direction to pass over the surface of the telegram. In this way a more faithful copy will be obtained in a shorter time.’

M. Lacour also observes that his system possesses a merit already pointed out by Mr. Varley, namely, that the instruments permit the passage of ordinary currents without revealing their presence, whence it follows that the accidental currents which often disturb telegraphic transmissions will have no effect on these systems.

M. Lacour began without applying an electro-magnetic system to his instrument in order to maintain the movement of the tuning-fork, but he soon saw that this accessory was indispensable, and he made the tuning-forks themselves electro-magnetic. It also occurred to him to convert the transmitted currents into pulsatory currents by inserting an induction coil in the circuit, which was also done by Mr. Elisha Gray. Finally, in order to obtain the immediate action of the tuning-forks and the immediate cessation of their action, he constructed them so as to reduce their inertia as much as possible. This was effected by inserting the two branches of the tuning-fork in the same coil and by lengthening its handle, and turning it back so that it might pass through a second coil, dividing into two branches and embracing the two vibrating branches, but without touching them. When a current traverses both coils, it produces, in the kind of horseshoe magnet formed by the two systems, opposite polarities which provoke a double reaction in the vibrating branches--a reaction by repulsion exerted by the two branches in virtue of the same polarity, and a reaction by attraction by the other two branches in virtue of their opposite polarities; and this double action is repeated by the movements of a contact breaker applied to one of the vibrating branches of the tuning-fork.

_Mr. Elisha Gray’s System._--According to the system originally patented, each sender, represented fig. 61, consists of an electro-magnet M M resting below a small copper tablet B S, in such a way that its poles pass through this tablet and are on a level with its upper surface. A steel plate A S is fixed above these poles; its tension can be regulated by means of a screw S; and another screw _c_ is placed on the plate, and is in electric communication with a local battery R′ by means of a Morse key. Below the plate A S there is a contact _d_ connected with the line wire L; this contact is met by the plate at the moment of its attraction by the electro-magnet, and breaks the current of a line battery P, which acts on the receiver of the opposite station. Finally, the electric communication established between the local battery R′ and the electro-magnet, as may be seen in the figure, produces vibrations in the steel plate A S at each lowering of the key, as in the case of ordinary vibrations--vibrations which, with a suitable tension of the plate and a given intensity of the battery R′, can produce a definite musical note. Moreover, since at each vibration the plate A S meets the contact, discharges of the line current take place through the line L, and react on the receiving instrument, causing it to reproduce exactly the same vibrations as those of the sending instrument.

The receiving instrument represented fig. 62 exactly resembles the one we have just described, except that there is no contact _d_ below the vibrating plate A S, and the contact _c_, instead of communicating with the line wire, is in electric connection with a register E and a local battery P. It follows from this arrangement that when the plate A S vibrates under the influence of the broken currents passing through the electro-magnet M M, similar vibrations are sent through the register; but if the electro-magnetic organ of this register is properly regulated, these vibrations can only produce the effect of a continuous current, and hence the length of the traces left on the instrument will vary with the duration of the sounds produced. In this way the registration of the dashes and dots which constitute the signs of the Morse vocabulary will be effected.

If it is remembered that the plate A S vibrates under the influence of electro-magnetic attractions more readily in proportion to their approximation in number to the vibrations corresponding to the fundamental sound it can emit, it becomes clear that if this plate is tuned to the same note as that of the corresponding instrument, it will be rendered peculiarly sensitive to the vibrations transmitted by the sender, and the other vibrations which may affect it will only act faintly. Moreover, a resonator placed above the plate will greatly increase this predisposition; so that if several systems of this kind, tuned to different notes, produce simultaneous transmissions, the sounds corresponding to the different vibrations will be in a certain sense selected and distributed, in spite of their combination, into the receivers for which they are specially adapted, and each of them may retain the traces of the sounds emitted by adding the register, which may be so arranged as to act as an ordinary Morse receiver. Mr. Gray states that the number of sending instruments and independent local circuits may be equal to that of the tones and semitones of two or more octaves, provided that each vibrating plate be tuned to a different note of the scale. The instruments may be placed side by side, and their respective local keys, arranged like the keys of a piano, will make it easy to play an air combining notes and chords; there may also be an interval between the instruments, which may be sufficiently far from each other to allow the employés to work without being distracted by sounds not intended for them.

In a new arrangement, exhibited at the Paris Exhibition, 1878, Mr. Gray considerably modified the way of working the various electro-magnetic organs which we have just described. In this case, the plates consist of tuning-forks with one branch kept in continual vibration at both stations, and the signals only become perceptible by intensifying the sounds produced. This arrangement follows from the necessity of keeping the line circuit always closed for multiple transmissions of this nature, so as to react with pulsatory currents, which are alone able, as we have already seen, to retain the individual character of several sounds simultaneously transmitted.

Under these conditions, the sender consists, as we see (fig. 63), of a bar tuning-fork, _a_, which is grooved for the passage of a runner, heavy enough to tune the fork to the desired note, and it oscillates between two electro-magnets _e_ and _f_ and two contacts I and G. The difference of resistance in the electro-magnets is very great: in the one _f_ the resistance is equal to 2¾ miles of telegraphic wire, in the other it does not exceed 440 yards. When electric communication is established as we see in the figure, the following effect takes place. Since the current of the local battery through the two electro-magnets is broken by the rest-contact of the Morse key H, the plate _a_ is subject to two contrary actions; but since the electro-magnet _f_ has more turns than the electro-magnet _e_, its action is preponderant, and the plate is attracted towards _f_, and produces a contact with the spring G, which opens a way of less resistance for the current. Since the current then passes almost wholly through G, _b_, 1, 2, B, the electro-magnet is now able to act; the plate _a_ is then attracted towards _e_, and, by producing a contact on the spring I, it sends the current of the line B P through the telegraphic line, if the key H is at the same time lowered on the sending contact: if not, there will be no effect in this direction, but since the plate _a_ has left the spring G, the first effect of attraction by the electro-magnet _f_ will be repeated, and this tends to draw the plate again towards _f_. This state of things is repeated indefinitely so as to maintain the vibration of the plate, and to send out signals corresponding with these vibrations whenever the key H is lowered. The elastic nature of the plate makes these vibrations more easy, and it ought also to be put in mechanical vibration at the outset.

The receiver, represented fig. 64, consists of an electro-magnet M, mounted on a sounding-box C, and having an armature formed by a tuning-fork L L firmly buttressed on the box by a cross bar T. There is a runner P on the armature, sliding in a groove, which makes it possible to tune the vibrations of the tuning-fork to the fundamental note of the sounding-box C, which is so arranged as to vibrate in unison with it. Under these conditions, the box as well as the tuning-fork will act as an analyser of the vibrations transmitted by the currents, and may set the register at work by itself reacting on a breaker of the local current. To obtain this result, a membrane of gold-beater’s skin or parchment must be stretched before the opening of the box, and a platinum contact must be applied to it, so arranged as to meet a metallic spring connected with any kind of register or a Morse instrument, when the membrane vibrates. As, however, in America the messages are generally received by sound, this addition to the system is not in use.

The instrument is not only regulated by the runner P, but also by a regulating screw V which allows the electro-magnet M to be properly adjusted. The regulating system is made more exact by the small screw V, and the instrument is connected with the line by the binding screw B. Of course this double arrangement is necessary for each of the sending systems.

As I have already said, seven different messages might theoretically be sent at once in this way, but Mr. Gray has only adapted his instrument for four; he has, however, made use of the duplex system, which allows him to double the number of transmissions, so that eight messages may be sent at the same time, four in one direction, and four in another.

Mr. Hoskins asserts that this system has been worked with complete success on the lines of the Western Union Telegraph Company, from Boston to New York, and from Chicago to Milwaukee. Since these experiments were made, fresh improvements have rendered it possible to send a much larger number of messages.

Mr. Gray has also, aided by Mr. Hoskins, devised a system by which telephonic messages may be sent on a wire previously used for Morse instruments. Mr. Varley had already solved this problem, but Mr. Gray’s system seems to have produced important results, and has therefore a claim to our attention. We do not, however, describe it here, since it is not within the lines marked out for us, and those who are interested in the subject will find all the necessary details in a paper inserted in the ‘Journal of the Society of Telegraphic Engineers, London,’ vol. vi.

_Mr. Varley’s System._--This system is evidently the earliest in date, since it was patented in 1870, and the patent describes the principle of most of the arrangements which have since been adopted by Messrs. Lacour, Gray, and Bell. It is based upon the use of his own musical telephone, which we have already described, but with some variations in its arrangement, which make it somewhat like the Reiss system.

It was Mr. Varley’s aim to make his telephone work in conjunction with instruments with ordinary currents, by the addition of rapid electric waves, incapable of making any practical change in the mechanical or chemical capacity of the currents which serve for the ordinary signals, yet able to make distinct signals, perceptible to the ear and even to the eye. He says: ‘An electro-magnet offers at first a great resistance to the passage of an electric current, and may consequently be regarded as a partially opaque body with respect to the transmission of very rapid inverse currents or of electric waves. Therefore, if a tuning-fork, or an instrument with a vibrating plate, tuned to a given note, be placed at the sending station, and so arranged as to be kept in constant vibration by magnetic influence, the current which acts upon it must be passed into two helices placed one above the other so as to constitute the primary helix of an induction coil: in this way it will be possible to obtain in two distinct circuits two series of rapidly broken currents, which will correspond to the two directions of the vibrations of the tuning-fork, and we shall also have the induced currents produced in the secondary helix by these currents, which may act on a third circuit. This third circuit may be placed in connection with a telegraphic line previously used by an ordinary telegraphic system, if a condenser is applied to it, and in this way two different transmissions may be obtained simultaneously.’

Fig. 65 represents the arrangement of this system. D is the vibrating plate of the tuning-fork designed to produce the electric contacts necessary to maintain it in motion. These contacts are at S and S′, and the electro-magnets which affect it are at M and M′. The induction coil is at I′, and the three helices of which it is composed are indicated by the circular lines which surround it. There is a Morse manipulator at A, another at A′, and the two batteries which work the system are at P and P′. The condenser is at C, and the telephone is at the end of the line L.

When the vibration of the plate D tends to the right, and the electric contact takes place at S′, the current of the battery P′, after traversing the primary helix, reaches the electro-magnets M M′, which give it an impulse in the contrary direction. When, on the other hand, it tends to the left, the current is sent through the second primary circuit, which will be balanced by the first. Consequently there will be a series of reversed currents in the induced circuit corresponding to the key A′, which will alternately charge and discharge the condenser C, thus sending into the line a corresponding series of electric undulations which will react on the telephone placed at the end of the line; and as the duration of the transmitted currents will vary with the time that the key A′ is lowered, a correspondence in the Morse code may be obtained in the telephone, while another correspondence is exchanged with the key A and the ordinary Morse receivers.

In order to render the vibratory signals visible, Mr. Varley proposes to use a fine steel wire, stretched through a helix and facing a narrow slit, to reproduce the vibrations. A light, which is intercepted by the wire, is placed behind the slit. As soon as a current passes, the wire vibrates and the light appears. A lens is placed so as to magnify the image of the luminous slit, and project it on a white screen while the wire is in vibration.

VARIOUS USES OF THE TELEPHONE.

_Its domestic application._--We have seen that telephones may be used with advantage in public and private offices: they can be set up at a much less expense than acoustic tubes, and in cases where the latter would never be employed. With the aid of the calls we have described, they offer the same advantages, and the connection between the instruments is more easily concealed. The difference of price in establishing them is in the ratio of one to seven.

For this purpose electro-magnetic telephones are evidently the best, since they require no battery and are always ready to work. They are already in use in many Government offices, and it is probable that they will soon be combined with electric bells for the service of hotels and of large public and private establishments: they may even be used in private houses for giving orders to servants and porters, who may thus save visitors from the fatigue of a useless ascent of several storeys.

In factories, telephones will certainly soon replace the telegraphic communication which has already become general. They may not only be used for ordinary messages, but to call for help in case of fire, and they will become an integral part of several systems already established for this purpose.

In countries which have free telegraphic communication, the telephone has already replaced in great measure the private telegraph instruments which have hitherto been in use; and if the same privilege is extended to France, no other mode of correspondence will be used.

_Its application to telegraphic service._--The advantage to be derived by the telegraphic service from the telephone is rather limited, since, as far as the speed of transmission is concerned, it is of less value than many of the telegraphic instruments now in use, and the messages which it produces cannot be registered. Yet in municipal offices not overburdened with messages they offer the advantage of not requiring a trained service. On longer lines their use would be of little value. The ‘Berne Telegraphic Journal’ has published some interesting remarks on this subject, of which the following is a summary.

1st. In order to send a message with the special advantages of the system, the sender ought to be able to address his correspondent without the intervention of an official. Those who are acquainted with the network of wires know this to be impossible. Intermediate offices for receiving messages are essential, and the public cannot be admitted to those set apart for sending and receiving; consequently the sender must deliver a written message.

2nd. If the message is written, the chief advantage of the instrument is lost, since it must be read and uttered aloud, which could not be done if expressed in a language with which the employés were unacquainted.

3rd. The instruments now in use at the telegraph offices can transmit messages more quickly than if they were spoken.

In Germany, however, a telephone service has been established in several telegraph offices, and its possible advantages are enumerated as follows in the official circular which created it:

‘The offices which will be opened to the public for the service of telephonic messages in Germany will be regarded as independent establishments; yet they will be in connection with the ordinary telegraph offices, which will undertake to send telephonic messages through their wires.

‘The transmission will take place as follows: The sending office will request the receiving office to prepare the instrument; as soon as the tubes are adjusted, the sending office will give the signal for despatching the verbal message.

‘The sender must speak slowly and clearly, without raising his voice; each syllable must be distinctly pronounced; the final syllables especially must be well articulated, and there must be a pause after each word, in order to give the receiver time to write it down.

‘When the telegram has been received, the employé at the receiving office must verify the number of words; then he must repeat through the telephone the whole message without pausing, so as to make sure that there is no mistake.

‘In order to ensure secrecy, the telephones are placed apart, where persons unconnected with the service cannot hear the verbal message, and the employés are forbidden to reveal to anyone the names of the correspondents.

‘The charge for telephonic messages, as for the ordinary telegraphic services, is at the rate of so much a word.’

The use of the telephone has also been suggested for verifying the perfect junction of telegraphic wires. It is certain that, if the junction is complete, no abnormal sounds will be heard, or only those which result from accidental currents; but if the junction is bad, the imperfect contacts which take place produce variations in electric intensity which are translated into the more or less marked sounds observed in the telephone.

M. Mauborgne, the electrician attached to the Northern Railway of France, has lately used the telephone instead of the galvanometer to ascertain the condition of the circuits in correspondence with the instruments in use for electric signals. The reactions produced on the galvanometer needle by the pieces of iron which are placed at the sides of the railway often make its indications uncertain, and a strong wind produces irregular movements in the instrument which interfere with observations. It was also necessary to place the galvanometer with due regard to the points of the compass, and to wait for the needle to settle, which involved loss of time. The operation is easily accomplished with the telephone, since the strokes of the call-bell are distinctly reproduced; it is made to ring by working the contacts which need verification, and in the same way the condition of the battery can be ascertained.

_Application to military purposes._--Since the telephone was invented, numerous experiments have been made in different countries to ascertain whether it would be of use in military operations. These experiments have hitherto been only moderately satisfactory, on account of the noise inseparable from an army, which generally makes it impossible to hear the telephone, and every means of intensifying its sounds has been eagerly sought. It was at first supposed that the discovery of the microphone had solved the problem, and I received many enquiries from military schools on the subject, but I have not been able to see that anything has been gained from this point of view. The telephone is, however, of great use in schools of artillery and rifle practice. Now that firearms carry so far, it has become necessary to be informed by telegraph of the points hit on the target, in order to judge of the accuracy of aim, and for this purpose telegraphic targets were suggested; but telephones are much to be preferred, and they are now used with good effect.

If the telephone is unsuited for the service of the flying telegraph in the field, it may be of great use in the defence of towns, to transmit the orders of the commandant to different batteries, and even for the exchange of correspondence with captive balloons sent to hover over fields of battle.

In spite of the difficulties attending its use, the experiment was made by the Russians in the late war: the cable wire of communication was 500 or 600 yards long, and so light that it could be laid by one man. The ‘Telegraphic Journal’ of March 15, 1878, states that the bad weather did not interfere with the working of the instruments; but the noise made it difficult to hear, and it was necessary to cover the head with a hood to intercept external sounds. This cannot be considered a satisfactory result, yet the telephone may be of great service to an army by intercepting the enemy’s messages: a bold man, provided with a pocket telephone, who placed himself in a retired spot, might divert the current of the enemy’s telegraphic wire into his telephone, and get possession of all his despatches, as we saw was the case at Clermont. He might even do this by diverting the current to earth or to a rail of the railway line. These are suggestions for future research, and it is probable that they may some day be turned to practical account.

_Its application to the navy._--The telephone may be of the greatest use in naval matters, for the service of electro-semaphores, for island forts and ships at anchor. M. Pollard says that ‘experiments made between the Préfecture Maritime at Cherbourg, the semaphores and the forts on the mole, demonstrate the advantage there would be in establishing telephones at these stations, since they would ensure an easy communication between the vessels of a squadron and the land they are approaching. By sinking small cables which come to the surface of the water along mooring chains, and terminate in buoys or cases which remain permanently in the harbour, the ships of war may in this way place themselves in communication with the Préfecture Maritime as they cast anchor, and, by temporarily connecting the vessels together with light cables, the admiral may communicate freely with the whole squadron.’

The telephone has been tried on board ship for transmitting orders, but without success, on account of the noise always going on in a vessel.

The telephone may be usefully applied to the service of submarine torpedoes. We have already seen how it may be applied in connection with the microphone, but it may also be used in firing the torpedoes after the exact position of the enemy’s ship has been ascertained from two reconnaissances taken from different parts of the coast.

The telephone, again, makes it possible to verify the condition of torpedoes, and to ascertain if there is any fault in the circuit within the explosives. For this purpose a very weak current has been used, and a galvanometer is not always able to indicate the fault, while the extreme sensitiveness of the telephone will do so in the simplest way.

Captain M’Evoy, of the American Army, suggested a way of ascertaining, while on shore, the condition of torpedoes under water, by connecting the buoys which support them with the land by means of a telephonic line. By inserting, in the buoy which supports the torpedo, metallic disks, so arranged as to vibrate with every movement caused by the waves upon the buoy, a continuous noise will be heard in the telephone, after the circuit has been completed by the metallic disks; and the noise will go on as long as the disks continue to oscillate, and will cease as soon as the buoy is completely covered by the water. When it ceases, therefore, if not affected by some accidental cause, it may be supposed that the enemy’s ship is passing over the buoy.

M. Trève, again, has shown that the telephone might be used with advantage for the telegraphic communication between vessels in tow, and M. des Portes has applied it with good effect to diving operations. In this instance, one of the glass panes in the helmet is replaced by a copper plate in which the telephone is framed, so that the diver need only make a slight movement of his head in order to receive or address communications to those in charge of the apparatus. With this system the keels of vessels may be examined, and an account given of their condition, without bringing up the divers, which has hitherto been necessary.

M. de Parville, the able and learned editor of the _Journal Scientifique_ and the science department of the _Journal des Débats_, has suggested a new and interesting application of the telephone. It concerns the possibility of making use of it to determine the precise position of the magnetic meridian, that is, the true direction of the magnetised needle.

For this purpose a Bell telephone is necessary, of which the magnetic core is formed of an iron rod a mètre in length, kept, by a suitable suspension, at nearly the same angle of inclination as a dipping-needle. This rod will be magnetised under the influence of terrestrial magnetism, and the telephone will be able to transmit the sounds produced by some sort of vibrator placed near its mouthpiece. These sounds will be strong in proportion to the degree of magnetisation of the bar; and if the telephone is turned round the horizon, keeping the bar at the same angle of inclination, the sounds transmitted to the receiving telephone will be greatest when the axis of the bar is in the plane of the magnetic meridian, and least when it is at 90°. It will therefore be possible to ascertain from the direction of the axis at the moment when the sounds are no longer heard, the exact inclination of the magnetic needle from north to south, for it will be given by the perpendicular to the line which is followed by the axis of the iron bar at that moment.

It is possible that, with this system, the disturbing influence on the magnetic needle of the mass of iron in iron-plated vessels might be almost destroyed, and a more exact orientation than that of the compass might be obtained. The same process may make it possible to estimate and measure the variations of terrestrial magnetism. M. de Parville has not himself tried to apply this system; but Mr. Blake’s experiments, of which we spoke in an early part of this work, make it probable that it might be done with advantage.

_Application to industry._--One of the earliest and most important applications of the telephone is that which was first made to the service of mines in England and America in the autumn of 1877. The great length of the galleries is well known, and had already involved the use of the electric telegraph for transmitting orders; but the miners did not understand how to work these instruments, and the service was ill performed. Thanks to the telephone, through which the first corner can send and receive a message, there is no longer any difficulty in the communication between the galleries and the surface of the mine.

The ventilation of mines can also be regulated by the aid of telephones. If one of these instruments is placed near a wheel kept in motion by the air which passes through the ventilating shaft, and another is placed in the inspector’s office he can ascertain by the sound if the ventilation is duly carried on, and if the machine works regularly.

_Application to scientific research._--M. d’Arsonval’s experiments, which we have already mentioned, show that the telephone can be used as an extremely sensitive galvanoscope; but since it can only produce sounds under the influence of broken currents, the circuit on which the experiment is made must be divided at rather close intervals. It has been seen that it is not even necessary to insert the telephone in the circuit: it may be influenced, when at a distance, either immediately or by the induction of the broken current on a circuit placed parallel to the first, and the force of these effects may be increased by the reaction of a core of iron, round which the inducing circuit is wound. The drawback to this system is that the direction of the current is not ascertained, so that it cannot be used as a measuring instrument; but, on the other hand, it is so sensitive, so easy to arrange, and so inexpensive, that it might be of the greatest use as a galvanoscope.

Mr. Warren de La Rue has also made use of the telephone in his researches into the electric discharges of high-tension batteries, in order to follow the different phases of the discharge during the luminous phenomena which it produces. In this way he ascertained that when a condenser is placed in connection with a battery formed of a considerable number of insulated elements, and is gradually discharged through a Geissler tube, a dull and faint sound is heard in the telephone, as long as the stratifications of light appear to be perfectly stable; but the sound becomes considerably stronger, and sometimes even piercing, in proportion to the diffusion of these stratifications, and to their approach to the point of extinction: whence it is shown that the discharge of a battery into tubes in which a vacuum has been made is intermittent.

Mr. Spottiswoode has repeated the same experiments with the discharges of Holtz machines, and with large condensers, and he found that the most piercing sounds produced by the telephone coincided with the greatest development of the stratifications. These sounds, however, sometimes ceased for a moment. It was even possible to ascertain, from the intensity of the sounds produced, the differences of tension which might be manifested in the charge of the condenser and the slackening of the machine’s motion, and the differences of intensity in these sounds might in some cases exceed an octave. The fall in the scale generally appeared in half-tones instead of gradually, and the introduction of resistances into the circuit modified the sounds very much: they might even be intensified by approaching the finger to the discharging tube.

From experiments made with the telephone between Calais and Boulogne, it appears that this instrument might be applied with advantage to the science of projectiles. In fact, in some artillery practice which took place on the shore at Boulogne, a telephone was placed close to the gun, and the explosion was heard at a distance of nearly two miles, where the projectile fell. It was possible to estimate its velocity by measuring the lapse of time between the moment when the projectile left the gun, and its fall. This calculation is usually made by observing the flash from the cannon’s mouth; but in some cases, as in a fog or in practice at long ranges, the telephone may be usefully substituted for ocular observation. On the field of battle, an observer, provided with a telephone and placed on a hill, might rectify from a distance the aim of his battery, which is generally established in a sheltered and less elevated place.

THE PHONOGRAPH.

Mr. Edison’s Phonograph, which has for the last year attracted so much attention, is an instrument which not only registers the different vibrations produced by speech on a vibrating plate, but reproduces the same words in correspondence with the traces registered. The first function of this instrument is not the result of a new discovery. Physicists have long sought to solve the problem of registering speech, and in 1856 Mr. Leo Scott invented an instrument well known to physicists under the name of Phonautograph, which completely solved the difficulty: this instrument is described in all the more detailed treatises on physics. But the second function of the Edison instrument was not realised nor even mentioned by Mr. Scott, and we are surprised that this able inventor should have regarded Mr. Edison’s invention as an injurious act of spoliation. We regret on his own account, since no one has wished to deprive him of the credit he deserves, that he should have published a pamphlet on the subject, couched in terms of such asperity, which proves nothing, and only states facts which were well known to all physicists. If any other person could claim the invention of the phonograph, at least in its most curious property of reproducing speech, it would certainly be M. Charles Cros; for in a sealed paper deposited at the Académie des Sciences, April 30, 1877, he pointed out the principle of an instrument by means of which speech might be reproduced in accordance with the marks traced on a register like that of the phonautograph.[19] Mr. Edison’s patent, in which the principle of the phonograph is first indicated, is dated July 31, 1877, and he was still only occupied with the repetition of the Morse signals. In this patent Mr. Edison described a mode of registering these signals by means of indentations traced with a stylus on a sheet of paper wound round a cylinder, and this cylinder had a spiral groove cut on its surface. The tracings thus produced were to be used for the automatic transmission of the same message, by passing it again under a stylus which should react on a current breaker. In this patent, therefore, nothing is said of the registration of speech or of its reproduction; but, as the ‘Telegraphic Journal’ of May 1, 1878, observes, the foregoing invention gave him the means of solving this double problem as soon as it was suggested to him. If we may believe the American journals, this suggestion soon came, and it was the result of an accident.

In the course of some experiments Mr. Edison was making with the telephone, a stylus attached to the diaphragm pierced his finger at the moment when the diaphragm began to vibrate under the influence of the voice, and the prick was enough to draw blood. It then occurred to him that if the vibrations of the diaphragm enabled the stylus to pierce the skin, they might produce on a flexible surface such distinct outlines as to represent all the undulations produced by the voice, and even that the same outlines might mechanically reproduce the vibrations which had caused them, by reacting on a plate capable of vibrating in the same way as that which he had already used for the reproduction of the Morse signals. From that moment the phonograph was discovered, since there was only a step between the idea and its realisation, and in less than two days the instrument was made and tried.

This is an ingenious story, yet we would rather believe that the discovery was made in a more serious spirit. In fact, such an inventor as Mr. Edison, who had discovered the electro-motograph, and had applied it to the telephone, was already on the way to discover the phonograph, and we think too well of his powers to attach much credit to this American romance. Besides, Mr. Edison was well acquainted with Mr. Scott’s phonautograph.

Mr. Edison’s phonograph was only patented in January 1877. Consequently, when we look at the principle of the invention, M. Cros undoubtedly may claim priority; but it is a question whether the system described in his sealed paper, and published in the _Semaine du Clergé_, October 8, 1877, would have been capable of reproducing speech. Our doubt seems justified by the unsuccessful attempts of the Abbé Leblanc to carry out M. Cros’ idea. When we have to do with such undulating and complex vibrations as those involved in the reproduction of articulate words, it is necessary that the stereotyping should in some sense be effected by the words themselves, and their artificial reproduction will necessarily fail to mark the slight differences which distinguish the delicate combinations of speech. Besides, the movements performed by a point confined to a groove that follows a sinusoidal curve cannot be effected with all the freedom necessary for the development of sounds, and the friction exerted on the two edges of the groove will often be of a nature to stifle them. A distinguished member of the Société de Physique, when I exhibited the phonograph to that society, justly said that Mr. Edison’s whole invention consisted in the thin metallic sheet on which the vibrations are inscribed; this sheet permits the movements of the vibrating plate to be directly stereotyped, and thereby the problem is solved. It was necessary to find such an expedient, and it was done by Mr. Edison, who is therefore the inventor of the phonograph.

After M. Cros, and before Mr. Edison, MM. Napoli and Marcel Deprez attempted to make a phonograph, but with so little success that they believed at one time the problem to be insoluble, and threw doubts on Mr. Edison’s invention when it was announced to the Société de Physique. They subsequently resumed their labours, and lead us to hope that they may eventually produce a phonograph of more perfect construction than that of Mr. Edison. We shall have more to say on this subject.