conclude very naturally that the rest of the planets are equally subject
to it? In case this power exists (which besides is proved) it must
increase in an inverse ratio of the squares of the distances. All,
therefore, that remains is, to examine how far a heavy body, which should
fall upon the earth from a moderate height, would go; and how far in the
same time, a body which should fall from the orbit of the moon, would
descend. To find this, nothing is wanted but the measure of the earth,
and the distance of the moon from it.

Thus Sir Isaac Newton reasoned. But at that time the English had but a
very imperfect measure of our globe, and depended on the uncertain
supposition of mariners, who computed a degree to contain but sixty
English miles, whereas it consists in reality of near seventy. As this
false computation did not agree with the conclusions which Sir Isaac
intended to draw from them, he laid aside this pursuit. A half-learned
philosopher, remarkable only for his vanity, would have made the measure
of the earth agree, anyhow, with his system. Sir Isaac, however, chose
rather to quit the researches he was then engaged in. But after Mr.
Picard had measured the earth exactly, by tracing that meridian which
redounds so much to the honour of the French, Sir Isaac Newton resumed
his former reflections, and found his account in Mr. Picard's
calculation.

A circumstance which has always appeared wonderful to me, is that such
sublime discoveries should have been made by the sole assistance of a
quadrant and a little arithmetic.

The circumference of the earth is 123,249,600 feet. This, among other
things, is necessary to prove the system of attraction.

The instant we know the earth's circumference, and the distance of the
moon, we know that of the moon's orbit, and the diameter of this orbit.
The moon performs its revolution in that orbit in twenty-seven days,
seven hours, forty-three minutes. It is demonstrated, that the moon in
its mean motion makes an hundred and fourscore and seven thousand nine
hundred and sixty feet (of Paris) in a minute. It is likewise
demonstrated, by a known theorem, that the central force which should
make a body fall from the height of the moon, would make its velocity no
more than fifteen Paris feet in a minute of time. Now, if the law by
which bodies gravitate and attract one another in an inverse ratio to the
squares of the distances be true, if the same power acts accor