In 1861 Reiss, of Freidrichsdorf, perfected an instrument which, by means of the vibrations of a diaphragm alternately completing and breaking the continuity of a galvanic circuit, reproduced musical sounds in an iron bar at a distance.
Varley, in 1870, obtained similar results to Reiss by the rapid charging and discharging of a condenser.
In the first of these experiments—viz.
Henry’s—the sound was mechanically conducted along the bar of wood from the strings of one piano to those of the other, which, being thrown into similar vibratory movements gave rise to similar sounds.
In the other experiments, on the contrary, the sounds were not due to the chemical conduction at all, but to currents of electricity. It has been explained that Reiss’ instrument was capable of reproducing musical sounds at a distance from their origin. Reiss’ may, therefore, be regarded as the original telephone. But, although able to reproduce a musical note or sound originating at a distance, this instrument failed altogether in the case of a word or a sentence, for the simple reason that the current of electricity which passes through the wires is an intermittent one. Musical sounds differ in tone, in intensity, and quality. The tone depends upon the number of vibrations produced in the air per second; when these are less than sixteen no sound is produced. The intensity is due to the extent or amplitude of the vibrations; and the quality or timbre, to the form of the undulations made by the vibrating particles of the atmosphere. Now, of all these qualities or varieties of sound, the first only, or the tone, can be reproduced by a current of intermittent electricity, so that Reiss’ is a tone telephone, and as such is only capable of redelivering a number of musical notes. To Professor A. Graham Bell alone belongs the merit of having invented an articulating or speaking telephone, or an apparatus by means of which not only tone, but intensity and timbre of sound—in short, speech in its entirety can be electrically conveyed from one point to another, no matter how distant. The practical result of this is that a conversation can be carried on, the distance by which the speakers may be separated being of no import. To the particular species of electricity by which this is accomplished Professor Bell has given the name ‘undulatory,’ in contradistinction to ‘intermittent’ or ‘pulsatory.’ The annexed plate, which is half the actual size of Bell’s articulating telephone, represents that instrument in section.
m m is a permanent bar-magnet, to the upper end of which is attached a soft iron core, which becomes magnetised by the permanent magnet. Surrounding the iron core is a coil of very fine insulated copper wire (b), the two ends of which are carried to the terminals (t t), by means of which one is connected with the line wire, and the other with the earth, d is a disc of thin iron plate, either tinned or japanned, about the size of a crown piece, and c is the cavity or mouth-piece. Upon applying the lips to this and speaking into it, the iron disc (d) vibrates towards the soft iron core, the result being that a current of induced electricity is set up in the coil (b), Which, being in connection by means of the telegraph wire with a precisely similar arrangement
at the other end of the line, reproduces there the spoken words by means of a corresponding disc. The magnet with its attachments are enclosed in a wooden case (a a, a a, a a); n n are screws which secure the iron disk (b); s is a screw for adjusting the distance between the polo of the magnet and the disk (b).
The extreme simplicity of Professor Bell’s telephone was the outcome of several antecedent experiments, worked out by forms of apparatus gradually diminishing in complexity.
The German physicist Helmholtz had previously shown that by the agency of a current of intermittent electricity passed through a tuning-fork, he could produce simultaneous vibrations in a number of other forks connected with the first by a wire, and that by varying the loudness of these vibrations by means of resonators, so as to combine the musical notes in different proportions, the resulting sound was an imitation of certain vowel sounds, or a copy of the timbre of sound.