nism analogous to that of the
shock. The X rays, if they are attributable to sudden variations in
the ether--that is to say, a variation of the two vectors of Hertz--
themselves produce within the atom a kind of electric impulse which
breaks it into two electrified fragments; _i.e._ the positive centre,
the size of the molecule itself, and the negative centre, constituted
by an electron a thousand times smaller. Round these two centres, at
the ordinary temperature, are agglomerated by attraction other
molecules, and in this manner the ions whose properties have just been
studied are formed.

Sec. 4. ELECTRONS IN METALS

The success of the ionic hypothesis as an interpretation of the
conductivity of electrolytes and gases has suggested the desire to try
if a similar hypothesis can represent the ordinary conductivity of
metals. We are thus led to conceptions which at first sight seem
audacious because they are contrary to our habits of mind. They must
not, however, be rejected on that account. Electrolytic dissociation
at first certainly appeared at least as strange; yet it has ended by
forcing itself upon us, and we could, at the present day, hardly
dispense with the image it presents to us.

The idea that the conductivity of metals is not essentially different
from that of electrolytic liquids or gases, in the sense that the
passage of the current is connected with the transport of small
electrified particles, is already of old date. It was enunciated by W.
Weber, and afterwards developed by Giese, but has only obtained its
true scope through the effect of recent discoveries. It was the
researches of Riecke, later, of Drude, and, above all, those of J.J.
Thomson, which have allowed it to assume an acceptable form. All these
attempts are connected however with the general theory of Lorentz,
which we will examine later.

It will be admitted that metallic atoms can, like the saline molecule
in a solution, partially dissociate themselves. Electrons, very much
smaller than atoms, can move through the structure, considerable to
them, which is constituted by the atom from which they have just been
detached. They may be compared to the molecules of a gas which is
enclosed in a porous body. In ordinary conditions, notwithstanding the
great speed with which they are animated, they are unable to travel
long distances, because they quickly find their road barred by a
material atom. They have to undergo innumerable impacts, w