The practical telephone handbook and guide to the telephonic exchange (1906)
Poole, Joseph · New York, Macmillan Co. · leaf 505
BOOK Cohens Galvanometer Set.—This is an instrument designed tomeasure the very weak telephonic speech currents. The chief partof it is a barretter or bolometer, in the shape of a smallelectric lamp having a very fine carbon filament (-6 mil in diameterand -| inch long) and a resistance of about… … Fig. 448a.—Connections of CohensGalvanometer Set being balanced by anotherbarretter. Through bothof these barretters a weaksteady current from a 2-volt battery is sent, so as tomaintain the filaments at acertain critical temperaturewhich gives the best resulton the galvanometer. Fig. 448a shows the…
Telephone
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