phant? They put it on the back
of a monstrous tortoise, and there they let the matter end. If every
animal in nature had been called upon, they would have been no nearer a
foundation. Most ancient peoples, indeed, made no effort to find a
foundation. The universe was a very compact little structure, mainly
composed of the earth and the great canopy over the earth which they
called the sky. They left it, as a whole, floating in nothing. And in
this the ancients were wiser than they knew. Things do not fall down
unless they are pulled down by that mysterious force which we call
gravitation. The earth, it is true, is pulled by the sun, and would fall
into it; but the earth escapes this fiery fate by circulating at great
speed round the sun. The stars pull each other; but it has already been
explained that they meet this by travelling rapidly in gigantic orbits.
Yet we do, in a new sense of the word, need foundations of the universe.
Our mind craves for some explanation of the matter out of which the
universe is made. For this explanation we turn to modern Physics and
Chemistry. Both these sciences study, under different aspects, matter
and energy; and between them they have put together a conception of the
fundamental nature of things which marks an epoch in the history of
human thought.

Sec. 1

The Bricks of the Cosmos

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 ap