Abstract :
Prior to 1918 only a few vacuum tubes of a simple type, usually a glass envelope enclosing a filament, a plate, and a control grid, were in use. Recently, especially in the war program, they constantly are being applied in new fields and the demands of the Armed Forces, particularly for communication and electrical detecting devices, have accelerated their use to an unprecedented degree. Even in civilian life the expansion will be noticeable: four or more types of tubes now will be used in every home radio receiver and in manufacturing processes many types of control equipment incorporate electronic devices.
