he
two coatings of a condenser having a difference of potential
sufficient to overcome what M. Bouty calls its dielectric cohesion. We
leave on one side this phenomenon, regarding which M. Bouty has
arrived at extremely important results by a very remarkable series of
experiments; but this question rightly belongs to a special study of
electrical phenomena which is not yet written.]

Let us therefore recognise with J.J. Thomson and the many physicists
who, in his wake, have taken up and developed the idea of Giese, that,
under the influence of the X rays, for reasons which will have to be
determined later, certain gaseous molecules have become divided into
two portions, the one positively and the other negatively electrified,
which we will call, by analogy with the kindred phenomenon in
electrolysis, by the name of ions. If the gas be then placed in an
electric field, produced, for instance, by two metallic plates
connected with the two poles of a battery respectively, the positive
ions will travel towards the plate connected with the negative pole,
and the negative ions in the contrary direction. There is thus
produced a current due to the transport to the electrodes of the
charges which existed on the ions.

If the gas thus ionised be left to itself, in the absence of any
electric field, the ions, yielding to their mutual attraction, must
finally meet, combine, and reconstitute a neutral molecule, thus
returning to their initial condition. The gas in a short while loses
the conductivity which it had acquired; or this is, at least, the
phenomenon at ordinary temperatures. But if the temperature is raised,
the relative speeds of the ions at the moment of impact may be great
enough to render it impossible for the recombination to be produced in
its entirety, and part of the conductivity will remain.

Every element of volume rendered a conductor therefore furnishes, in
an electric field, equal quantities of positive and negative
electricity. If we admit, as mentioned above, that these liberated
quantities are borne by ions each bearing an equal charge, the number
of these ions will be proportional to the quantity of electricity, and
instead of speaking of a quantity of electricity, we could use the
equivalent term of number of ions. 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 qua