More than two thousand years ago the first men of science, the Greeks of
the cities of Asia Minor, speculated on the nature of matter. You can
grind a piece of stone into dust. You can divide a spoonful of water
into as many drops as you like. Apparently you can go on dividing as
long as you have got apparatus fine enough for the work. But there must
be a limit, these Greeks said, and so they supposed that all matter was
ultimately composed of minute particles which were indivisible. That is
the meaning of the Greek word "atom."
Like so many other ideas of these brilliant early Greek thinkers, the
atom was a sound conception. We know to-day that matter is composed of
atoms. But science was then so young that the way in which the Greeks
applied the idea was not very profound. A liquid or a gas, they said,
consisted of round, smooth atoms, which would not cling together. Then
there were atoms with rough surfaces, "hooky" surfaces, and these stuck
together and formed solids. The atoms of iron or marble, for instance,
were so very hooky that, once they got together, a strong man could not
tear them apart. The Greeks thought that the explanation of the universe
was that an infinite number of these atoms had been moving and mixing in
an infinite space during an infinite time, and had at last hit by chance
on the particular combination which is our universe.
This was too simple and superficial. The idea of atoms was cast aside,
only to be advanced again in various ways. It was the famous Manchester
chemist, John Dalton, who restored it in the early years of the
nineteenth century. He first definitely formulated the atomic theory as
a scientific hypothesis. The whole physical and chemical science of that
century was now based upon the atom, and it is quite a mistake to
suppose that recent discoveries have discredited "atomism." An atom is
the smallest particle of a chemical element. No one has ever seen an
atom. Even the wonderful new microscope which has just been invented
cannot possibly show us particles of matter which are a million times
smaller than the breadth of a hair; for that is the size of atoms. We
can weigh them and measure them, though they are invisible, and we know
that all matter is composed of them. It is a new discovery that atoms
are not indivisible. They consist themselves of still smaller particles,
as we shall see. But the atoms exist all the same, and we may still say
that they are the bricks of which the material universe is built.
[Illustration: _Photo: Elliott & Fry._