Heroes of the Telegraph [69]
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
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