The receiver, [Fig. B], consists of an electro-magnet, m m, which reposes upon a sounding-box, u w, and whose wire coils are respectively connected with the metallic conductor and with the earth or metallic return-conductor.
Opposite the electro-magnet, m m, stands an armature, which is connected with a lever, i, which is long as possible, but light and broad.
The lever, i, is fastened, pendulum-wise, to the support, k, and its movements are regulated by the screw, l, and the spring, p.
In order to improve the action of the apparatus, this receiver can be placed in one focus of an elliptically arched cavity of corresponding size, in which case, then, the ear of him who is listening to the reproduced tones may be placed at the second focus of this cavity.
The action of the two apparatuses here described, is the following:—
In a condition of rest the galvanic circuit is closed.
In the apparatus, [Fig. A], by speaking (singing, or leading into it the tones of an instrument) into the tube a b, in consequence of the condensation and rarefaction of the air present in this tube, there will be evoked a motion of the membrane closing the tube at its narrow end, corresponding to this condensation or rarefaction. The lever, c d, follows the motion of the membrane, and opens and closes the galvanic circuit at d g, so that by each condensation of the air in the tube an opening, and at each rarefaction a closing of the galvanic circuit ensues.
In consequence of this process, the electro-magnet of [Fig. B] (the receiver) will be demagnetised and magnetised correspondingly with the condensations and rarefactions of the mass of air in the tube A, a b [the mouth-piece of the transmitter], and the armature belonging to the magnet will be set into vibrations similar to those of the membrane in the transmitting apparatus. The plank, i, connected with the armature, conveys these similar vibrations to the air surrounding the apparatus, [Fig. B], which finally transmits to the ear of the listener the tones thus produced.
We are not, therefore, dealing here with a propagation of sound through the electric current, but only with a transference to another place of the tones that have been produced, by a like cause being brought into play at this second place, and a like effect produced.