The combination, with an electro-magnet, of a plate of iron or steel, or other material capable of inductive action, which can be thrown into vibration by the movement of surrounding air or by the attraction of a magnet.
(inductive action; can be thrown; into vibration; by the movement of surrounding air or by the attraction of a magnet)
inductive action
can be thrown
into vibration by the movement of surrounding air or by the attraction of a magnet