Circular permanent magnet with annular gap 1 3/8"

Circular permanent magnet with annular gap 1 3/8" to 1", part of Oliver Lodge’s microphone amplifier or relay, 1898 (British patent 9712 of 1898), a precursor of the moving-coil loudspeaker

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Science Museum: Making the Modern World Gallery

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Radio Communication
Object Number:
Sir Oliver Lodge.

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