Electricity for everybody; its nature and uses explained (1895)
Atkinson, Philip · New York, The Century Co. · leaf 237
THE TELEGRAPH AND TELEPHONE. 221 … employed for this purpose; opposite which is mounted a diaphragm a, like that in the Bell receiver. Just behind this is a little carbon disk, &, attached to a brass disk, suspended by a metal spring c, so that the carbon disk comes opposite the center of the diaphragm. The end of another…
Electricity
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