The principle of magnetic recording was invented by a Danish telephone engineer called Valdemar Poulsen in 1899. He used an electromagnet to record the tiny electric currents from a telephone to magnetise a steel wire. This recreated tiny currents in the electromagnet when it was replayed. All tape and video recorders still work this way.
Cartoons copyright (C) 1988-1994 Tim Hunkin. All rights reserved.