Pole pieces for same magnet altering to annular gap, 1898
- Made:
- 1898
Pole pieces for same magnet altering to annular gap approximately 3 7/8" to 3 5/16", part of Oliver Lodge’s microphone amplifier or relay, 1898 (British patent 9712 of 1898) ), a precursor of the moving-coil loudspeaker
