American telegraphy and encyclopedia of the telegraph; systems, apparatus, operation (1909)
Maver, William, jr. [from old catalog] · New York, Maver publishing company · leaf 117
7d/as(rumenfy … In the figure, w is a short wire of high resistance always in the circuit. S is abent lever hinged at x^ and normally held against the up-stop c, a short distance fromp, by the tension of the wire w. When, however, the wire w is heated by a strongcurrent it expands and permits the lever s to drop…
Telegraph
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