P. 1017. The researches established by Reis on the 26th of October, 1861, in Frankfurt[38] have already shown that if the current interruptions follow one another almost continuously and very rapidly, in a spiral arranged with a thin iron core, the iron wire can be set into longitudinal vibrations, whereby therefore the same is constrained to reproduce tones of different pitch.
[Here follows a reference to Petrina’s Electric Harmonica.]
From the communications made known by Legat, it follows that “the ideas concerning the reproduction of tones by means of electro-galvanism which were put forward some time since by Philipp Reis of Friedrichsdorf, before the Physical Society, and the meeting of the Free German Institute in Frankfort-on-the-Main,” relate to similar arrangements. “What has hitherto been attained in the realisation of this project,” Legat announces in his report, and we extract therefrom only that part which gives an explanation of the disposition of the telegraphic apparatus, with which it is said to be possible to produce the vibrations and the excitement of tones in any desired manner, and by which the employment of electro-galvanism is said to make it possible “to call 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.”
This apparatus consists of the tone-indicator (transmetteur) and the tone-receiver (récepteur). The tone-indicator ([Fig. 34], p. 109) consists of a conical tube, a b, having a length of about 15 cm., a front aperture of about 10 cm., and a back aperture of about 4 cm., the choice of the material and the greater length of which is said to be indifferent, while a greater width is said to be injurious; the surface of the inner wall should be as smooth as possible. The narrow back aperture of the tube is closed by a membrane, o, of collodion, and upon the centre of the circular surface formed by this membrane rests the one end, c, of the lever, c d, the supporting-point of which, e, being held by a support, remains in connection with the metallic circuit. This lever, the arm, c e, of which must be considerably longer than c d, should be as light as possible, so that it can easily follow the movements of the membrane, because an uncertain following of the lever, c d, will produce impure tones at the receiving station. During the state of rest the contact, d g, is closed, and a weak spring, n, keeps the lever in this state of rest. Upon the metallic support, f, which is in connection with one pole of the battery, there is a spring, g, with a contact corresponding to the contact of the lever, c d, at d, the position of which is regulated by means of the screw, h. In order that the effect of the apparatus may not be weakened by the produced waves of air communicating themselves towards the back part, a disc “of about 50 (?) cm. diameter, which rests fixedly upon the exterior wall of the tube,” is to be placed above the tube, a b, at right angles with its longitudinal axis.
Fig. 34.