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. Here, however, it must not be overlooked that the preceding apparatus reproduces, indeed, the original vibrations in equal number, but that equal strength in the reproduced vibrations has not yet been attained, and the production of these is reserved for a completion of the apparatus. One consequence of this temporary incompleteness of the apparatus, is that the slighter differences of the original vibrations are more difficult to discern: that is to say, the vowel appears more or less indistinct, the more so since each tone is dependent, not only on the number of vibrations of the medium, but also on the condensation or rarefaction of the same. By this it is also explained, that, in the practical investigations heretofore carried on, chords, melodies, etc., were transmitted with marvellous fidelity; while single words uttered as in reading, speaking, and the like, were perceptible more indistinctly. Nevertheless, here also the inflexions of the voice, the modulations of interrogation, exclamation, wonder, command, &c., attained distinct expression.