Appletons' cyclopaedia of applied mechanics: a dictionary of mechanical engineering and the mechanical arts (1880)
D. Appleton and Company, Benjamin, Park, 1849-1922 · New York, D. Appleton · leaf 895
ulating or Speaking Telephones.—Of these instruments three classes may be recognized : 860 TELEPHONE. 1. Those which operate through variations in the electro-motive force of the current; 2. Those which the current passes; and 3^es produced by the current. 4105. 1. IflOSe WHICH unciace miuugii… … I. Telephones depending on Changes in Electro-motive Force.—BelVs Telephone was inventedby Prof. Alexander Graham Bell in 1876. It consists essentially of a bar-magnet surrounded by acoil of insulated wire which is in circuit with the conducting wire. In front of the magnet a thinmembrane or…
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