第51章

Bourseul's idea seems to have attracted little notice at the time, and was soon forgotten. Even the Count du Moncel, who was ever ready to welcome a promising invention, evidently regarded it as a fantastic notion. It is very doubtful if Reis had ever heard of it. He was led to conceive a similar apparatus by a study of the mechanism of the human ear, which he knew to contain a membrane, or 'drum,' vibrating under the waves of sound, and communicating its vibrations through the hammer-bone behind it to the auditory nerve. It therefore occurred to him, that if he made a diaphragm in imitation of the drum, and caused it by vibrating to make and break the circuit of an electric current, he would be able through the magnetic power of the interrupted current to reproduce the original sounds at a distance.

In 1837-8 Professor Page, of Massachusetts, had discovered that' a needle or thin bar of iron, placed in the hollow of a coil or bobbin of insulated wire, would emit an audible 'tick' at each interruption of a current, flowing in the coil, and that if these separate ticks followed each other fast enough, by a rapid interruption of the current, they would run together into a continuous hum, to which he gave the name of 'galvanic music.' The pitch of this note would correspond to the rate of interruption of the current. From these and other discoveries which had been made by Noad, Wertheim, Marrian, and others, Reis knew that if the current which had been interrupted by his vibrating diaphragm were conveyed to a distance by a metallic circuit, and there passed through a coil like that of Page, the iron needle would emit a note like that which had caused the oscillation of the transmitting diaphragm. Acting on this knowledge, he constructed a rude telephone.

Dr. Messel informs us that his first transmitter consisted of the bung of a beer barrel hollowed out in imitation of the external ear. The cup or mouth-piece thus formed was closed by the skin of a German sausage to serve as a drum or diaphragm. To the back of this he fixed, with a drop of sealing-wax, a little strip of platinum, representing the hammer-bone, which made and broke the metallic circuit of the current as the membrane oscillated under the sounds which impinged against it. The current thus interrupted was conveyed by wires to the receiver, which consisted of a knitting-needle loosely surrounded by a coil of wire fastened to the breast of a violin as a sounding-board. When a musical note was struck near the bung, the drum vibrated in harmony with the pitch of the note, the platinum lever interrupted the metallic circuit of the current, which, after traversing the conducting wire, passed through the coil of the receiver, and made the needle hum the original tone. This primitive arrangement, we are told, astonished all who heard it. [It is now in the museum of the Reichs Post-Amt, Berlin.]

Another of his early transmitters was a rough model of the human ear, carved in oak, and provided with a drum which actuated a bent and pivoted lever of platinum, making it open and close a springy contact of platinum foil in the metallic circuit of the current. He devised some ten or twelve different forms, each an improvement on its predecessors, which transmitted music fairly well, and even a word or two of speech with more or less perfection. But the apparatus failed as a practical means of talking to a distance.

The discovery of the microphone by Professor Hughes has enabled us to understand the reason of this failure. The transmitter of Reis was based on the plan of interrupting the current, and the spring was intended to close the contact after it had been opened by the shock of a vibration. So long as the sound was a musical tone it proved efficient, for a musical tone is a regular succession of vibrations. But the vibrations of speech are irregular and complicated, and in order to transmit them the current has to be varied in strength without being altogether broken. The waves excited in the air by the voice should merely produce corresponding waves in the current. In short, the current ought to UNDULATE in sympathy with the oscillations of the air.