d to-day these laws
of the conservation of energy and of matter are more firmly established
than ever.

The thing that has gone by the board is the old idea of the atoms as the
indivisible and irreducible minima of the material universe. For not
only do all the radioactive substances give off particles of helium gas
positively electrified, but _all bodies, no matter what their
composition_, can by suitable treatment, such as exposing them to
ultra-violet light, or raising them to incandescence, be made to _give
off electrons_ or negatively charged particles, and _these electrons are
always the same no matter from what kind of substance they come_. In a
somewhat similar way, we always get positively electrified particles of
the mass of the hydrogen atom, or about 1,760 times the mass of the
electron, whenever we send an electric charge through a gas at very low
pressure, _no matter what the kind of gas_. Whether or not these
positive units will yet prove susceptible of being split up into smaller
particles comparable to the electrons, is merely a subject for
conjecture. We have no proof that they will. At the present time what we
call matter seems to be composed of these positive units and of the
electrons which are about 1/1760 as great; and in the present state of
our knowledge these facts suffice to explain all the properties of
matter. Thus we can either say that electricity is composed of matter,
or say that matter is composed of electricity; and human language at
best is such a clumsy vehicle of thought that scientifically and
philosophically the one statement is as correct and as reasonable as the
other.

And probably we shall never be able to learn any more than this. We have
arrived at a sort of box-within-a-box theory of the make-up of matter.
By a very elaborate system of unpacking, or by some violent external
force that makes the inside burst open, as it were, we seem to be able
to make pieces fly off from the atoms, these pieces being then projected
into space with enormous force and velocity. There are theories galore
of the structure of the atom; but as Prof. E.P. Lewis has said, most of
these theories are so impossible as to be absurd, or so speculative that
"they suggest no experimental tests for their validity."[2] Just at
present Rutherford's theory of the structure of the atom is quite
popular. This postulates a nucleus composed of a group of positive units
and electrons, with an excess of the posit