J. Thomson observes that before these recent discoveries the
investigator could not detect a gas unless about a billion
molecules of it were present, and it must be remembered that the
spectroscope had already 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