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CHAPTER XX NEGATRONS FROM PHOTO-ELECTRIC ELEMENTS
(1) It' is a property of metals to shed or emit negatrons. The surface of any metal is always surrounded by an extremely thin cloud of negatrons which have escaped from that surface. The number of negatrons escaping from a square inch of metallic surface at ordinary room temperature is considerable, but since (as we have seen) a fantastically enormous number of negatrons is needed to constitute even a minute electrical charge or current, the electrical effect of the negatrons thus escaping is extremely small, and difficult to detect. t
(2) If, however, the metal is heated to the point of incandescence, the emission of negatrons from its surface is vastly increased. (3) If this emission takes place in air, its effect is to ionize or disrupt the atoms of air immediately surrounding the emitting surface, the energy of the emission being consumed to no beneficial purpose. If free negatrons emitted by any metal are to be made useful, the emission must take place in a vacuum. Exceptions to the statement just made will be discussed later on. See Pages 506 and 518.
There is no practical way of raising the temperature of a metal to the point of incandescence, when the metal is in vacuum, except by passing an electric current through it. If the current be large enough, and the resistance of the metal high enough, incandescence is attained, just as in the case of any ordinary electric lamp filament. Negatrons are emitted by the filament of any incandescent lamp. However, they serve no useful purpose in the lamp. It will be worth while, nevertheless, to consider the life history of a negatron emitted from an electric lamp filament. The negatron, on leaving the filament, continues out through the vacuum by virtue of
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