The practical telephone handbook and guide to the telephonic exchange (1906)
Poole, Joseph · New York, Macmillan Co. · leaf 127
circuit are favour-able, spark across a comparatively great thickness of an in-sulator rather than pass through many turns of wire ; all 104 PRACTICAL TELEPHONE HANDBOOK instruments should, therefore, be provided with some form ofprotector, in which a short and favourable spark gap—usuallythrough…
Telephone
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