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.