Each apparatus consists, as is seen from the above illustration, of two parts: the Telephone proper, A, and the Reproduction apparatus [Receiver], C. These two parts are placed at such a distance from each other, that singing, or the tones of a musical instrument, can be heard from one station to the other in no way except through the apparatus itself. Both parts are connected with each other, and with the battery, B, like ordinary telegraphs. The battery must be capable of effecting the attraction of the armature of the electromagnet placed at the side of station A (3-4 six-inch Bunsen’s elements suffice for several hundred feet distance). The galvanic current goes then from B to the screw, _d_, thence through the copper strip to the little platinum plate at the middle of the membrane, then through the foot, _c_, of the angular piece to the screw, _b_, _in whose little concavity a drop of quicksilver is put_. From here the current then goes through the little telegraph apparatus, _e-f_, then to the key of station C, and through the spiral past _i_ back to B. [Illustration: Fig. 29.] If now sufficiently strong tones are produced before the sound-aperture, S, the membrane and the angle-shaped little hammer lying upon it are set in motion by the vibrations; the circuit will be once opened and again closed for each full vibration, and thereby there will be produced in the iron wire of the spiral at station C the same number of vibrations which there are perceived as a tone or combination of tones (chord). By imposing the little upper case (Oberkästchen) firmly upon the axis of the spiral the tones at C are greatly strengthened. Besides the human voice (according to my experience) there also can be reproduced the tones of good organ-pipes from F--c' and those of a piano. For the latter purpose A is placed upon the sounding-board of the piano. (Of thirteen triads (Dreiklänge) a skilled experimentor could with all exactness recognise ten). As regards the telegraph apparatus placed at the side, it is clearly unnecessary for the reproduction of tones, but it forms a very agreeable addition for convenient experimenting. By means of the same, it is possible to make oneself understood right well and certainly by the other party. This takes place somewhat in the following manner: After the apparatus has been completely arranged, one convinces oneself of the completeness of the connexion and the strength of the battery by opening and closing the circuit, whereby at A the stroke of the armature is heard, and at C a very distinct ticking. By rapid alternate opening and closing at A it is asked at C whether one is ready for experimenting, whereupon C answers in the same manner. Simple signals can by agreement be given from both stations by opening and closing the circuit one, two, three, or four times; for example:-- 1 beat = Sing. 2 beats = Speak, &c.