"THE EDISON EFFECT"

Radio Record, Volume I, Issue 52, 13 July 1928, Page 15

"THE EDISON EFFECT"

ACTION INSIDE A EULB. fz is many vears ago since Edison | made his now famous experiment of surrounding one of the Hmbs of an electric filament lamp with a metal cylinder, which led to the discovery that electrical charges were given out from the filament and could be receiyed by the surrounding cylinder. This is known as the "Edison effect, :;and it was this same effect which led Fleming to the invention of the 2electrode yalve which was, of course, the forerunner cf the 3-electrode or amplifying valve developed by Dr. de Forest. In an.electrie filament lamp, especially of the old-fashioned carbon filament type, there is another phenomenon taking place, which consists in the gradual disintegration of the filament ,and the liberation of particles of the filament substance, these particles depositing themselves upon the interior surface of the glass bulb Fi is in consequence of this latter effect that the well-known blackening is produced, which was much more noticeable with

earbon filament lamps than it is with the present-day metal filament type. The disintegration of incandescent filaments does not in itself account for the electrical emission, and although some of the actual material particles detached from the filament may be electrically charged, and may therefore help to carry the emission current, the latter is carried mainly by electrons sent out from the filament. In proper circumstances, the actual disintegration of the filament may be made exceedingly small, so as to be negligible; but the electronic emission may at the same time be quite large, and it is, indeed, one of the aims of electric lamp manufacturers to reduce the disintegration of the filament to a minimum, whilst it is the aim of radio valve manufacturers to reduce the disintegration and‘at.the same time to increase the electronic emission.