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 Pole pieces for same magnet altering to annular gap, 1898 1898
Pole, for Royal Mail Coach, by Waude and Co., London, England, 1815-1830 Pole for Royal Mail Coach 1815-1825
