ELECTROPHONE, an instrument devised by Dr. Strethill Wright for producing sound by electric currents of high tension. In its simplest form, the electroplione consists of two metallic plates separated by a sheet of cartridge-paper, the whole being closely pressed together by a heavy weight or screw. Such an instrument, when its plates are connected with the terminals of a small induction-coil, forms a sonorous condenser, the note of which varies with the rapidity of action in the electrotome or contact-breaker. The more compli cated electrophone communicated to the royal Scottish society of arts, 25th April, 1864, by Dr. Wright,is composed of four curved plates of the thinnest sheet-zinc, each 2 by 4 ft., and each separated from its neighbor by a double layer of imitation silvered paper, the sil vered sides being in apposition to the zinc. The first and third, and second and fourth plates are connected by fine wires, which also connect the instrument with the induc tion-coil. When this instrument is connected with a small coil, the terminals of which afford a spark almost inaudible, it becomes charged and discharged with each impulse of current, each charge being attended by a sonorous tap given out by the whole mass of metal thrown into vibration, and the rapid succession of taps producing a prolonged trumpet-note, the power of which may be increased.by adding battery-power to the coil. The electrophone has been recommended by its author for use as a telegraphic relay capable of giving two or four signs with a single wire, with the advantage over other relays that perfection of contact was not necessary to its working. Fig. 1 shows the mode of working the electrophone as a double relay with four signals and the galvanom eter of Thomson; .A represents the needle of the galvanometer, B and C the wires communicating with an electrophone. When the needle is deflected to the right, it falls on the points B and C, and sounds the electrophone through B, A, C. The signals are produc el by long and short contacts, as in the code of Morse. The second set of signals are produced by the reversal of the line-current, which throws the needle on the points of the arrangement D connected with a second electrophone of different tone. The electrophone has been
employed as a lecture table instrument to report to a large audience results of processes which can only be rendered sensible by the most delicate galvanometric apparatus. Fig. 2 shows the adaptation of the electrophonc to the galvanometer. AB represents the needle of the galvanometer suspended by a silk fiber, C; D is a small vessel of mercury communicating by a fine wire with the center of the needle; while a similar wire, attached to the end of the needle B, dips into the curved trough EF, containing distilled water. The wires inserted into D and F connect the coil with the electrophone, the current passing through F, E, B, D. When the needle is deflected, the tract of water between E and F is shortened, and the electrophone gives forth a gradually increasing sound. By a delicate system of levers attached to the wrist, as in the spligymograph (q.v.), the rhythm and character of the human pulse, and its variation in disease, may be indicated to the class by the physician.
Further, the electrophone may be adapted to the telephone by making the telephone mem brane act the part of a make-and-break for the current circulating in the 'primary wire of induction-coil. This can easily be done by leading the current through the membrane, and through a spring carrying a platinum point, which presses lightly against a piece of platinum attached to the center of the mem brane. If the sounds uttered into the tele phone be sufficiently strong to make the membrane so to vibrate as to cause actual separation between the platinum surfaces, they will be reproduced with great loudness in the electrophone; but if, as in the case of speaking, they be merely able to cause variations of pressure at the surfaces, they will be but imperfectly heard. Bence the electrophone succeeds best with singing (see TELE PHONE), and a song gently, snug .in ;Due place may be repeateil trumpet-tones in another hundreds of .yards digant.. vitized by Microsoft 0