e electric and magnetic fields produced in the
interior of bodies; and it is even conceivable that there may be
produced, under the influence of these actions, a tendency to
determine orientation, that is to say, that a reason can be seen why
matter may be crystallised.[50]

[Footnote 50: The reader should, however, be warned that a theory has
lately been put forth which attempts to account for crystallisation on
purely mechanical grounds. See Messrs Barlow and Pope's "Development
of the Atomic Theory" in the _Transactions of the Chemical Society_,
1906.--ED.]

All the experiments effected on the conductivity of gases or metals,
and on the radiations of active bodies, have induced us to regard the
atom as being constituted by a positively charged centre having
practically the same magnitude as the atom itself, round which the
electrons gravitate; and it might evidently be supposed that this
positive centre itself preserves the fundamental characteristics of
matter, and that it is the electrons alone which no longer possess any
but electromagnetic mass.

We have but little information concerning these positive particles,
though they are met with in an isolated condition, as we have seen, in
the canal rays or in the X rays.[51] It has not hitherto been possible
to study them so successfully as the electrons themselves; but that
their magnitude causes them to produce considerable perturbations in
the bodies on which they fall is manifest by the secondary emissions
which complicate and mask the primitive phenomenon. There are,
however, strong reasons for thinking that these positive centres are
not simple. Thus Professor Stark attributes to them, with experiments
in proof of his opinion, the emission of the spectra of the rays in
Geissler tubes, and the complexity of the spectrum discloses the
complexity of the centre. Besides, certain peculiarities in the
conductivity of metals cannot be explained without a supposition of
this kind. So that the atom, deprived of the cathode corpuscle, would
be still liable to decomposition into elements analogous to electrons
and positively charged. Consequently nothing prevents us supposing
that this centre likewise simulates inertia by its electromagnetic
properties, and is but a condition localised in the ether.

[Footnote 51: There is much reason for thinking that the canal rays do
not contain positive particles alone, but are accompanied by negative
electrons of slow velocity. Th