This apparent digression from the aim set forth was necessary in order to indicate that as soon as it is possible for us to create anywhere, and in any manner whatever, vibrations whose curves and magnitudes are similar to the vibrations of any given tone, or of any given combination of tones, we shall have the same impression as this original tone or this original combination of tones would have produced upon us.
The apparatus hereafter described offers the possibility of creating these vibrations in every fashion that may be desired, and the employment of electro-galvanism gives us the possibility of calling into life, at any given distance, vibrations similar to the vibrations that have been produced, and in this way to reproduce at any place the tones that have been originated at another place.
In Fig. 4, Plate II.,[26] herewith presented, A is the transmitter (Tonabgeber), and B the receiver (Tonempfänger), which two instruments are set up at different stations. I make, however, the preliminary remark that the manner of joining the instruments for interchangeable use backward and forward is here omitted for the sake of clearness, and the more so because the whole is not here propounded as a final fact, but in order to bring that which has been hitherto accomplished to the knowledge of a wider circle. The possibility of the working of the apparatus to a greater distance than that which at present limits in practice the direct working of the galvanic current may also be left out of consideration, since these points may be easily rendered possible by mechanical precautions, and do not affect the essential part of the phenomena now described.
Let us next turn to the transmitter, Fig. A. It is put into communication on one side with the metallic conductor leading to the neighbouring station, and by means of this with the receiver, Fig. B; on the other side it is connected, by means of the electro-motive power, C, with the earth or a metallic return-conductor.
The transmitter, Fig. A, consists of a conical tube, _a b_, of about 15 centimetres length, 10 centimetres in the front, and 4 centimetres in the back aperture.
(In the practical investigations it has been established that the choice of material for this tube is without influence on the use of the apparatus, and moreover a greater length of the same for the certainty [of action] of the apparatus is without effect. A greater width of the cylinder spoils the usefulness of the apparatus; and it is recommended that the interior surface be as smooth as possible.)