Thomas Edison working drawing: Battery technology (also vacuum tubes), Two Lamp Tubes, June 6, 1927
In electronics, a vacuum tube is a device controlling electric current through a vacuum in a sealed container. The container is often thin transparent glass in a roughly cylindrical shape. Famous scientists who experimented with vacuum tubes included Thomas Edison, who made their first practical use with his electric light bulb. This 1926 drawing in Edison’s own hand shows how he combined two of his most important inventions and one of his key discoveries into a new device. The inventions were the light bulb and the rechargeable nickel-iron battery. The discovery was the “Edison effect,” emission of electrons from a hot cathode into a vacuum.