able to see a wonderful
bird's-eye view. He would lose, no doubt, the details of towns and
villages; the features in such a landscape would be whole continents and
whole oceans, in so far as the openings between the clouds would permit
the earth's surface to be exposed.

At this stupendous elevation he could try one of the most interesting
experiments that was ever in the power of a philosopher. He could test
whether the earth's attraction was felt at such a height, and he could
measure the amount of that attraction. Take for the experiment a cork, a
marble, or any other object, large or small; hold it between the
fingers, and let it go. Everyone knows what would happen in such a case
down here; but it required Sir Isaac Newton to tell what would happen in
such a case up there. Newton asserts that the power of the earth to
attract bodies extends even to this great height, and that the marble
would fall. This is the doctrine that we can now test. We are ready for
the experiment. The marble is released, and, lo! our first exclamation
is one of wonder. Instead of dropping instantly, the little object
appears to remain suspended. We are on the point of exclaiming that we
must have gone beyond the earth's attraction, and that Newton is wrong,
when our attention is arrested; the marble is beginning to move, so
slowly that at first we have to watch it carefully. But the pace
gradually improves, so that the attraction is beyond all doubt, until,
gradually acquiring more and more velocity, the marble speeds on its
long journey of a quarter of a million of miles to the earth.

But surely, it will be said, such an experiment must be entirely
impossible; and no doubt it cannot be performed in the way described.
The bold idea occurred to Newton of making use of the moon itself, which
is almost a quarter of a million of miles above the earth, for the
purpose of answering the question. Never was our satellite put to such
noble use before. It is actually at each moment falling in towards the
earth. We can calculate how much it is deflected towards the earth in
each second, and thus obtain a measure of the earth's attractive power.
From such enquiries Newton was able to learn that a body released at the
distance of 240,000 miles above the surface of the earth would still be
attracted by the earth, that in virtue of the attraction the body would
commence to move off towards the earth--not, indeed, with the velocity
with which a body fa