Desk Telephone Apparatus
Siemens & Halske
The device had a resonance plate with four parallel coal cores linked by two carbon bars. Current passed through a connecting carbon block and branched out through two pairs of connecting cores. Current then passed into the opposite carbon block and passed through it into a chain. Sound pronounced in front of a resonance plate was then heard in the telephone. This device was used in France as a public phone and in private households.