The practical telephone handbook and guide to the telephonic exchange (1906)
Poole, Joseph · New York, Macmillan Co. · leaf 166
OM M UNICA TION TELEPHONES 141 this defect, and so produce a secrecy system. One of themost promising of these was known as Slopers in which,by the use of a special switch, the ordinary connection to thereturn wires of two engaged stations were cut off by mutualarrangement, and the two ordinary… … and as the lines were not twisted in proper pairs, it was stillpossible to faintly overhear the conversation. Sloper & Parsons System.—This is an improvement on thelast-mentioned, which appears to fulfil the secrecy require-ments with great success. Fig. 154 gives the connections oftwo…
Telephone
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