A metal can, in fact, be electrified, that is to say, may
possess an excess of positive or negative electrons which cannot
easily leave it in ordinary conditions. To cause them to do so would
need an appreciable amount of work, on account of the enormous
difference of the specific inductive capacities of the metal and of
the insulating medium in which it is plunged.
Electrons, however, which, on arriving at the surface of the metal,
possessed a kinetic energy superior to this work, might be shot forth
and would be disengaged as a vapour escapes from a liquid. Now, the
number of these rapid electrons, at first very slight, increases,
according to the kinetic theory, when the temperature rises, and
therefore we must reckon that a wire, on being heated, gives out
electrons, that is to say, loses negative electricity and sends into
the surrounding media electrified centres capable of producing the
phenomena of ionisation. Edison, in 1884, showed that from the
filament of an incandescent lamp there escaped negative electric
charges.
Pages:
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335