eady gone far beyond ordinary chemical analysis in
detecting the presence of substances in minute quantities. Since these
discoveries we can recognise a single molecule, bearing an electric
charge.

With these extraordinary powers the physicist is able to penetrate
a world that lies immeasurably below the range of the most powerful
microscope, and introduce us to systems more bewildering than those of
the astronomer. We pass from a portentous Brobdingnagia to a still more
portentous Lilliputia. It has been ascertained that the mass of the
electron is the 1/1700th part of that of an atom of hydrogen, of which,
as we saw, billions of molecules have ample space to execute their
terrific movements within the limits of the letter "o." It has been
further shown that these electrons are identical, from whatever source
they are obtained. The physicist therefore concludes--warning us that
on this further point he is drawing a theoretical conclusion--that the
atoms of ordinary matter are made up of electrons. If that is the case,
the hydrogen atom, the lightest of all, must be a complex system of some
1700 electrons, and as we ascend the scale of atomic weight the clusters
grow larger and larger, until we come to the atoms of the heavier metals
with more than 250,000 electrons in each atom.

But this is not the most surprising part of the discovery. Tiny as the
dimensions of the atom are, they afford a vast space for the movement of
these energetic little bodies. The speed of the stars in their courses
is slow compared with the flight of the electrons. Since they fly out of
the system, in the conditions we have described, at a speed of between
90,000 and 100,000 miles a second, they must be revolving with terrific
rapidity within it. Indeed, the most extraordinary discovery of all is
that of the energy imprisoned within these tiny systems, which men have
for ages regarded as "dead" matter. Sir J. J. Thomson calculates that,
allowing only one electron to each atom in a gramme of hydrogen, the
tiny globule of gas will contain as much energy as would be obtained by
burning thirty-five tons of coal. If, he says, an appreciable fraction
of the energy that is contained in ordinary matter were to be set free,
the earth would explode and return to its primitive nebulous condition.
Mr. Fournier d'Albe tells us that the force with which electrons repel
each other is a quadrillion times greater than the force of gravitation
that brings ato