The practical telephone handbook and guide to the telephonic exchange (1906)
Poole, Joseph · New York, Macmillan Co. · leaf 172
160.—Full size … B D FT? V R Eth p r\ tfc] w%\ iP^lPiH nr^ K Fig. 161.—Full size and 162 show a form in which the restoring is done automati-cally by means of a local battery current. The indicator is a kind of double drop, being similar to atubular drop, o, with another shorter ironclad coil, R, attachedto one end…
Telephone
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