No, we will create another world, and add another power to it that
shall keep them apart. That power shall be what is called the force
of inertia, which is literally no power at all; it is an inability
to originate or change motion. If a body is at rest, inertia is
that quality by which it will forever remain so, unless acted upon
by some force from without; and if a body is in motion, it will
continue on at the same speed, in a straight line, forever, unless
it is quickened, retarded, or turned from its path by some other
force. Suppose our newly created sun is 860,000 miles in diameter.
Go away 92,500,000 miles and create an earth eight thousand miles
in diameter. It instantly feels the attractive power of the sun
drawing it to itself sixty-eight [Page 9] miles a second. Now, just
as it starts, give this earth a push in a line at right angles with
line of fall to the sun, that shall send it one hundred and
eighty-nine miles a second. It obeys both forces. The result is that
the world moves constantly forward at the same speed by its inertia
from that first push, and attraction momentarily draws it from its
straight line, so that the new world circles round the other to the
starting-point. Continuing under the operation of both forces, the
worlds can never come together or fly apart.

They circle about each other as long as these forces endure; for
the first world does not stand still and the second do all the
going; both revolve around the centre of gravity common to both.
In case the worlds are equal in mass, they will both take the same
orbit around a central stationary point, midway between the two.
In case their mass be as one to eighty-one, as in the case of the
earth and the moon, the centre of gravity around which both turn
will be 1/81 of the distance from the earth's centre to the moon's