The practical telephone handbook and guide to the telephonic exchange (1906)
Poole, Joseph · New York, Macmillan Co. · leaf 442
Fig 206. Fig. 407 and to prevent loss by Foucault currents, such iron shouldbe in the form of very fine iron wire, wound at right anglesto the conductor coils, such as shown in Figs. 406 and 407,which show the form of coil suggested by Prof. Pupin,the iron wire being varnished, to prevent side…
Telephone
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