The practical telephone handbook and guide to the telephonic exchange (1906)
Poole, Joseph · New York, Macmillan Co. · leaf 184
st possibletrouble or delay. Separate keys were formerly used forspeaking and ringing; but these are now usually joined to-gether, and operated with one lever, this resulting in muchimprovement in their working. Kellogg Combined Listening and Ringing Key.—This key,shown in Figs. 180 and 181, is…
Telephone
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