Identifier: practicaltelepho00pool (find matches)
Title: The practical telephone handbook and guide to the telephonic exchange
Year: 1906 (1900s)
Authors: Poole, Joseph
Subjects: Telephone
Publisher: New York, Macmillan Co.
Contributing Library: Northeastern University, Snell Library
Digitizing Sponsor: Boston Library Consortium Member Libraries

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kind of instrument is now used by the National Tele-phone Co. The Battery Switch-Bell.—For short private lines, and fortelephones between different parts of the same building,signalling is often done by means of batteries instead of bymagneto-generators, an ordinary trembler electric bell beingthen used for calling attention. Fig. 120 gives a view of awall-pattern instrument of this class. The connections aremade both on the series system and on the shunt system, aswith magneto switch-bells. Part of the ringing battery SUB-STATION INSTRUMENT CONNECTIONS 115 (which for lines under 1J miles in length need not exceed fourcells) is used for the microphone battery. As one end of theringing battery is joined to earth or to return wire it is necessaryto insulate the primary circuit from direct contact with theswitch-hook and to use an independent contact for closing theprimary circuit of the microphone, otherwise part of the currentwould be working through the line wires. A contact for the
Text Appearing After Image:
Fig. 119 purpose is, therefore, provided on an insulated conductorattached to or moved by the switch-hook when a hand-micro-telephone is not used. To close the battery circuit for ringingthe distant station a push button, or lever key, is used,connected to one of the line wires, and provided with a backcontact. The connections of such an instrument on the series system are shown in Fig. 121, and on the shunt system in Fig.122. If an earth return is used instead of a second-line wire, n6 PRACTICAL TELEPHONE HANDBOOK the terminals L 2 are connected to earth as indicated in dottedlines.A different type of battery wall instrument is shown in Fig. 123, this beingfitted with a cradleswitch and hand-micro - telephone,also with a 4-point instrumentplug and jack, bymeans of whichthe H.M.T. can bereadily discon-nected. Fig. 124 showsa table set for bat-tery working asmade by MessrsEricsson & Co.The connectionsare shown in Fig.125, in which theloop line, or line-and - earth ter-minals, are s

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