ccupied by the cork or by the lead would be the same; and even the
feather itself would fall through sixteen feet in one second, if it
could be screened from the interference of the air. Try this experiment
where we like, in London, or in any other city, in any island or
continent, on board a ship at sea, at the North Pole, or the South Pole,
or the equator, it will always be found that any body, of any size or
any material, will fall about sixteen feet in one second of time.

Lest any erroneous impression should arise, we may just mention that the
distance traversed in one second does vary slightly at different parts
of the earth, but from causes which need not at this moment detain us.
We shall for the present regard sixteen feet as the distance through
which any body, free from interference, would fall in one second at any
part of the earth's surface. But now let us extend our view above the
earth's surface, and enquire how far this law of sixteen feet in a
second may find obedience elsewhere. Let us, for instance, ascend to the
top of a mountain and try the experiment there. It would be found that
at the top of the mountain a marble would take a little longer to fall
through sixteen feet than the same marble would if let fall at its base.
The difference would be very small; but yet it would be measurable, and
would suffice to show that the power of the earth to pull the marble to
the ground becomes somewhat weakened at a point high above the earth's
surface. Whatever be the elevation to which we ascend, be it either the
top of a high mountain, or the still greater altitudes that have been
reached in balloon ascents, we shall never find that the tendency of
bodies to fall to the ground ceases, though no doubt the higher we go
the more is that tendency weakened. It would be of great interest to
find how far this power of the earth to draw bodies towards it can
really extend. We cannot attain more than about five or six miles above
the earth's surface in a balloon; yet we want to know what would happen
if we could ascend 500 miles, or 5,000 miles, or still further, into the
regions of space.

Conceive that a traveller were endowed with some means of soaring aloft
for miles and thousands of miles, still up and up, until at length he
had attained the awful height of nearly a quarter of a million of miles
above the ground. Glancing down at the surface of that earth, which is
at such a stupendous depth beneath, he would be