The development of ac rotary machines

After that Michael Faraday (1791–1867) produced an electromotive force between the axis and edge of a disc kept in rotation and subjected to the axial magnetism of a fixed permanent magnet in 1831, several researchers and experimenters pursued efficient electro-generation designs capable the replacing expensive electrochemical batteries [1]. It was soon clear that a stronger effect could be achieved with an electromagnetic multiplier (i.e. a coil of several winding) subject to the alternating action of a permanent magnet, obtained by mutual rotation.