The practical telephone handbook and guide to the telephonic exchange (1906)
Poole, Joseph · New York, Macmillan Co. · leaf 291
the trunk line, and a red one for thejunction line or a second trunk line, the corresponding clearinglamps being coloured white and red. Two operators keys areprovided for each pair of cords—one a combined ringing andspeaking key for use on the trunk lines, and the other a ringingand disconnecting… … •^gr^y conditions for speaking on long trunk lines. For similarreasons an extra receiver is provided for each operator. Thisa TRUNK-LINE EXCHANGES 265 when not required, is hung on a hook, which disconnects it,as shown. The relay r1 works in conjunction with relay R for closingthe circuit of the…
Telephone
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