The telephone system of the British post office. A practical handbook (1901)
Herbert, Thomas Ernest · London, New York, Whittaker and Co. · leaf 116
h Post Office. lol CHAPTER XVI. Up and Down Call Wires. In order to have a readier means of obtaining the Companys attention,each operator has upon her switch section a special press button termeda call wire key, which, when depressed, joins her speaking apparatus to ■V 3—V :ZI ^ j\ Figure 87. the… … Jljnjoe/ necessary, and in order to meet this the call wires at either end passthrough switches, which put the call wires on to indicators. At the PostOffice this switch consists of six holes upon the test board. The centralpair of holes are connected to the call wire, the top and bottom pairs 102…
Telephone · Postal service
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