Heroes of the Telegraph

by John Munro

Before he left Scotland Mr. Graham Bell had turned his attention to telephony, and in Canada he designed a piano which could transmit its music to a distance by means of electricity. At Boston he continued his researches in the same field, and endeavoured to produce a telephone which would not only send musical notes, but articulate speech.

If it be interesting to trace the evolution of an animal from its rudimentary germ through the lower phases to the perfect organism, it is almost as interesting to follow an invention from the original model through the faultier types to the finished apparatus.

In 1860 Philipp Reis, as we have seen, produced a telephone which could transmit musical notes, and even a lisping word or two; and some ten years later Mr. Cromwell Fleetwood Varley, F.R.S., a well-known English electrician, patented a number of ingenious devices for applying the musical telephone to transmit messages by dividing the notes into short or long signals, after the Morse code, which could be interpreted by the ear or by the eye in causing them to mark a moving paper. These inventions were not put in practice; but four years afterwards Herr Paul la Cour, a Danish inventor, experimented with a similar appliance on a line of telegraph between Copenhagen and Fredericia in Jutland. In this a vibrating tuning-fork interrupted the current, which, after traversing the line, passed through an electro-magnet, and attracted the limbs of another fork, making it strike a note like the transmitting fork. By breaking up the note at the sending station with a signalling key, the message was heard as a series of long and short hums. Moreover, the hums were made to record themselves on paper by turning the electro-magnetic receiver into a relay, which actuated a Morse printer by means of a local battery.

Mr. Elisha Gray, of Chicago, also devised a tone telegraph of this kind about the same time as Herr La Cour. In this apparatus a vibrating steel tongue interrupted the current, which at the other end of the line passed through the electro-magnet and vibrated a band or tongue of iron near its poles. Gray's 'harmonic telegraph,' with the vibrating tongues or reeds, was afterwards introduced on the lines of the Western Union Telegraph Company in America. As more than one set of vibrations—that is to say, more than one note—can be sent over the same wire simultaneously, it is utilised as a 'multiplex' or many-ply telegraph, conveying several messages through the same wire at once; and these can either be interpreted by the sound, or the marks drawn on a ribbon of travelling paper by a Morse recorder.

Gray also invented a 'physiological receiver,' which has a curious history. Early in 1874 his nephew was playing with a small induction coil, and, having connected one end of the secondary circuit to the zinc lining of a bath, which was dry, he was holding the other end in his left hand. While he rubbed the zinc with his right hand Gray noticed that a sound proceeded from it, which had the pitch and quality of the note emitted by the vibrating contact or electrotome of the coil. 'I immediately took the electrode in my hand,' he writes, 'and, repeating the operation, found to my astonishment that by rubbing hard and rapidly I could make a much louder sound than the electrotome. I then changed the pitch of the vibration, and found that the pitch of the sound under my hand was also changed, agreeing with that of the vibration.' Gray lost no time in applying this chance discovery by designing the physiological receiver, which consists of a sounding-box having a zinc face and mounted on an axle, so that it can be revolved by a handle. One wire of the circuit is connected to the revolving zinc, and the other wire is connected to the finger which rubs on the zinc. The sounds are quite distinct, and would seem to be produced by a microphonic action between the skin and the metal.

All these apparatus follow in the track of Reis and Bourseul—that is to say, the interruption of the current by a vibrating contact. It was fortunate for Bell that in working with his musical telephone an accident drove him into a new path, which ultimately brought him to the invention of a speaking telephone. He began his researches in 1874 with a musical telephone, in which he employed the interrupted current to vibrate the receiver, which consisted of an electro-magnet causing an iron reed or tongue to vibrate; but, while trying it one day with his assistant, Mr. Thomas A. Watson, it was found that a reed failed to respond to the intermittent current. Mr. Bell desired his assistant, who was at the other end of the line, to pluck the reed, thinking it had stuck to the pole of the magnet. Mr. Watson complied, and to his astonishment Bell observed that the corresponding reed at his end of the line thereupon began to vibrate and emit the same note, although there was no interrupted current to make it. A few experiments soon showed that his reed had been set in vibration by the magneto-electric currents induced in the line by the mere motion of the distant reed in the neighbourhood of its magnet. This discovery led him to discard the battery current altogether and rely upon the magneto-induction currents of the reeds themselves. Moreover, it occurred to him that, since the circuit was never broken, all the complex vibrations of speech might be converted into sympathetic currents, which in turn would reproduce the speech at a distance.

Reis had seen that an undulatory current was needed to transmit sounds in perfection, especially vocal sounds; but his mode of producing the undulations was defective from a mechanical and electrical point of view. By forming 'waves' of magnetic disturbance near a coil of wire, Professor Bell could generate corresponding waves of electricity in the line so delicate and continuous that all the modulations of sound could be reproduced at a distance.

As Professor of Vocal Physiology in the University of Boston, he was engaged in training teachers in the art of instructing deaf mutes how to speak, and experimented with the Leon Scott phonautograph in recording the vibrations of speech. This apparatus consists essentially of a thin membrane vibrated by the voice and carrying a light stylus, which traces an undulatory line on a plate of smoked glass. The line is a graphic representation of the vibrations of the membrane and the waves of sound in the air.

On the suggestion of Dr. Clarence J. Blake, an eminent Boston aurist, Professor Bell abandoned the phonautograph for the human ear, which it resembled; and, having removed the stapes bone, moistened the drum with glycerine and water, attached a stylus of hay to the nicus or anvil, and obtained a beautiful series of curves in imitation of the vocal sounds. The disproportion between the slight mass of the drum and the bones it actuated, is said to have suggested to him the employment of goldbeater's skin as membrane in his speaking telephone. Be this as it may, he devised a receiver, consisting of a stretched diaphragm or drum of this material having an armature of magnetised iron attached to its middle, and free to vibrate in front of the pole of an electro-magnet in circuit with the line.

This apparatus was completed on June 2, 1875, and the same day he succeeded in transmitting SOUNDS and audible signals by magneto-electric currents and without the aid of a battery. On July 1, 1875, he instructed his assistant to make a second membrane-receiver which could be used with the first, and a few days later they were tried together, one at each end of the line, which ran from a room in the inventor's house at Boston to the cellar underneath. Bell, in the room, held one instrument in his hands, while Watson in the cellar listened at the other. The inventor spoke into his instrument, 'Do you understand what I say?' and we can imagine his delight when Mr. Watson rushed into the room, under the influence of his excitement, and answered,'Yes.'