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 273
ELECTRIC ELEVATORS 2,927 … Pigs. 4,198 and 4,199.—Elevator safety consisting ofwedges forced apart by right and left hand threadsturned by a drum. This method gives a varyingpressure which gradually increases as the drumturns, and consequently produces an increasingretardation of the motion of the car. The gover-nor A, is…
Electrical engineering
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