He found that if a magnetised steel needle or a very small bundle of extremely thin iron wires is magnetised and placed in the interior of a small coil, the ends of which are connected to two long collecting wires, then an electric wave started from a Hertz oscillator at a distance causes an immediate demagnetisation of the iron.
"Hertzian Wave Wireless Telegraphy"
John Ambrose Fleming
The demagnetisation of the iron which ensues produces an electromotive force in the secondary coil and causes a deflection of the galvanometer, and this deflection will continue and remain steady if the oscillation persists.
"Hertzian Wave Wireless Telegraphy"
John Ambrose Fleming