Replica liquid transmitter as used by Bell in the first transmission of speech in 1876.

Accurate replica of device used on March 10, 1876.

The Liquid Transmitter was one of earliest devices for converting sound into electric current; we now call such a device a microphone.

The liquid transmitter works like this. It is first connected by wires to a battery and a receiver (listening device). Bell used a vibrating reed device as a receiver with the ear pressed firmly against the reed.

In the liquid transmitter, one end of a wire was attached to a diaphragm and the other end just touched the surface of acidified water in a container below the diaphragm. Acidified water conducts electricity.

When someone spoke with their mouth close to the diaphragm, the diaphragm vibrated, making the wire to dip up and down in the water, the resistance of the receiver-transmitter circuit changing in sympathy. The changing resistance caused a similarly changing current through the circuit, which caused the reed in the receiver to vibrate and reproduce the original sounds.

Physical Description

Consists of speaking tube ending in diaphragm. Needle attached to diaphragm projects into small cup of acidified water.

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