Ferdinand Braun and the Cathode Ray Tube
The indicator tube developed by "Braun" in the 1890's leasured electrical quantities by the deflection of an electron beam. It was an ancestor of the oscilloscope and television picture tube.
The Induction Coil
This antecedent of the modern transformer served for nearly a century as the principal source of high-voltage electric current. It figured prominently in three epochal discoveries
The First Electron Tube
In 1904 John Ambrose Fleming wrote Guglielmo Marconi: "I have been receiving signals on an aerial with nothing but a mirror galvanometer and my device." The device was the original thermionic vacuum diode