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.)
The narrow hinder aperture of the cylinder is closed by a membrane, o, of collodion, and on the middle of the circular surface formed by this membrane rests one end, c, of the lever, c d, the fulcrum (point of support), c, of which, supported on a bearing, remains joined to the metallic conductor.
The choice of the length of the two arms of the lever, c e and e d, is determined by the laws of force of levers. It is recommended that the arm, c e, be constructed longer than the arm e d, in order to bring the smallest movement at c into action at d with the greatest possible force; but, on the other hand, it is desirable to make the lever itself as light as possible, in order that it may follow the motions of the membrane. An uncertain following of the lever, c d, produces impure tones at the receiving station. In the condition of rest the contact, d g, is closed, and a delicate spring, n, holds the lever firmly in this position of rest.
The second part of this apparatus, the pillar, f, consists of a metallic support, which is united with one pole of the battery, C, while the second pole of the battery is carried to the metallic conductor of the other station.
Upon the support, f, there is a spring, g, with a contact, which corresponds to the contact at d of the lever c d, and whose position is regulated by a screw, h.
In order not to weaken the action of the apparatus by the communication of the air-waves which are produced in using the apparatus, against the back of the membrane, it is recommended, in using the apparatus, to place over the tube, a b, at right angles to its longitudinal axis, a screen of about 50 centimetres diameter, which fixes tight upon the outer surface of the tube.