avitation. Thus we can picture
the earth and all the planets as if they were swinging round the sun,
held by invisible strings. It is the combination of two forces that
keeps them in their places--the first force and the sun's pull. It is
very wonderful to think of. Here we are swinging in space on a ball that
seems only large to us because we are so much smaller ourselves; there
is nothing above or below it but space, yet it travels on day by day and
year by year, held by invisible forces that the brain of man has
discovered and measured.

Of course, every planet gives a pull at every other planet too, but
these pulls are so small compared with that of the sun that we need not
at present notice them. Then we come to another point. We said that
every body pulled every other body in proportion to their weights and
their distance. Now, gravity acts much more strongly when things are
near together than when they are far away from each other; so that if a
smaller body is near to another somewhat larger than itself, it is
pulled by it much more strongly than by a very much larger one at a
considerably greater distance. We have an instance of this in the case
of the earth and moon: as the earth responds to the pull of the sun, so
the moon responds to the pull of the earth. The moon is so comparatively
near to the earth that the earth-pull forces her to keep on going round
and round, instead of leaving her free to circle round the sun by
herself; and yet if you think of it the moon does go round the sun too.
Recall that game we had when the sun was in the middle, and the two
smaller girls, representing the earth and moon, went round it. The
moon-child turned round the earth-child, but all the while the
earth-child was going round the sun, so that in a year's time the moon
had been all round the sun too, only not in a straight line. The moon is
something like a dog who keeps on dancing round and round you when you
go for a walk. He does go for the walk too, but he does much more than
that in the same time. Thus we have further completed our idea of our
world. We see it now hanging in space, with no visible support, held in
its place by two mighty forces; spinning on year after year, attended by
its satellite the moon, while we run, and walk, and cry, and laugh, and
play about on its surface--little atoms who, except for the brain that
God has given them, would never even have known that they are
continually moving on through en