Hawkins electrical guide ... : questions, answers & illustrations : a progressive course of study for engineers, electricians, students and those desiring to acquire a working knowledge of electricity and its applications ; a practical treatise (1914)
Hawkins, N. (Nehemiah), 1833-1928 · New York : T. Audel & Co. · leaf 56
. THE TELEPHONE 2,149 Four ringing keys are used at the central office exchange. Superimposed current is obtained by connecting in series a sourceof alternating current, the negative side of which is grounded, withtwo sets of storage battery, giving out direct current. Ringing lead wires are…
Electrical engineering
Internet Archive · Brigham Young University · Public Domain Mark 1.0. Free to use for anything.
