History, theory, and practice of the electric telegraph (1866)
Prescott, George B.(George Bartlett),1830-1894 · Boston, Ticknor and Fields · leaf 97
78 ELECTRIC TELEGRAPH APPARATUS. lines in this country. It consists of a lever mounted on a hori-zontal axis, with a knob of ivory for the hand at the extremity of … Fig. 38. the long arm, which is at the left in the cut. This lever isthrown up by a spring, so as to avoid contact with the button onthe frame below, except when the lever is depressed for the pur-pose of completing the circuit. A regulating screw is seen at
Telegraph
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