Giese was a forerunner, but
his ideas could not triumph so long as there were no means of
observing conduction in simple circumstances. But this means has now
been supplied in the discovery of the X rays. Suppose we pass through
some gas at ordinary pressure, such as hydrogen, a pencil of X rays.
The gas, which till then has behaved as a perfect insulator,[29]
suddenly acquires a remarkable conductivity. If into this hydrogen two
metallic electrodes in communication with the two poles of a battery
are introduced, a current is set up in very special conditions which
remind us, when they are checked by experiments, of the mechanism
which allows the passage of electricity in electrolysis, and which is
so well represented to us when we picture to ourselves this passage as
due to the migration towards the electrodes, under the action of the
field, of the two sets of ions produced by the spontaneous division of
the molecule within the solution.
[Footnote 29: At least, so long as it is not introduced between the
two coatings of a condenser having a difference of potential
sufficient to overcome what M.
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