. The Bell System technical journal . Pig 6—Carbon pencil type microphone, mounted on a sounding board, demonstrated by Hughes in Fig. 7—The Blake transmitter using a platinum contact pressed against a carbon block. THE CARBON MICROPHONE 169 are compressed between two polished carbon electrodes which areimmersed in the granular mass in such a way that the particles havemore freedom of movement than in the Hunnings instrument. Thisrelieves excess pressure without undue packing.

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Keywords: ., bookcentury1900, bookdecade1920, booksubjecttechnology, bookyear1