The telephone system of the British post office. A practical handbook (1901)
Herbert, Thomas Ernest · London, New York, Whittaker and Co. · leaf 76
ces by means of the spiral spring, the tension upon which may beregulated by revolving the screw at the top of the instrument. This screwcarries a h jok about a quarter of an inch long, to which the spiral springis attached. The tongue of the relay is provided with a platinum tip,which is brought… … //Uiit<i- Figure 50. The telephone at the subscribers end is joined upas shown in Figure 50.It will be seen that the battery employed consists of four cells, two ofwhich are used also for the microphone and also as the local battery for thebell. The permanent current, usually about 7…
Telephone · Postal service
Internet Archive · Cornell University Library · Public Domain Mark 1.0. Free to use for anything.
