The telephone system of the British post office. A practical handbook (1901)
Herbert, Thomas Ernest · London, New York, Whittaker and Co. · leaf 192
this board a battery and indicator (as described in the case ofPost OfiSce up call wires) is connected to each call wire when the dividedlever is moved over to the left (Figure 139). Immediately a subscriberdepresses his call key this indicator falls. The night operator then movesthe lever… … Figure 139. cords upon the nearest multiple. Of course, when the day operators leavethey remove their telephones, which would otherwise bridge across the callwire and actuate the night indicators. Having considered the electrical details of the system, we may nowpass to the construction of the…
Telephone · Postal service
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