For the excitement produced by a
given pencil of X rays, the number of ions liberated will be fixed.
Thus, from a given volume of gas there can only be extracted an
equally determinate quantity of electricity.
The conductivity produced is not governed by Ohm's law. The intensity
is not proportional to the electromotive force, and it increases at
first as the electromotive force augments; but it approaches
asymptotically to a maximum value which corresponds to the number of
ions liberated, and can therefore serve as a measure of the power of
the excitement. It is this current which is termed the _current of
saturation_.
M. Righi has ably demonstrated that ionised gas does not obey the law
of Ohm by an experiment very paradoxical in appearance. He found that,
the greater the distance of the two electrode plates from each, the
greater may be, within certain limits, the intensity of the current.
The fact is very clearly interpreted by the theory of ionisation,
since the greater the length of the gaseous column the greater must be
the number of ions liberated.
Pages:
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316