tion of that side of the earth, which counteracts the gravitation of
bodies near its surface. For the earth and moon may be considered as two
cannon balls of different sizes held together by a chain, and revolving
once a month round a common center of gravity between them, near the
earth's surface; at the same time that they perform their annual orbits
round the sun. Whence the centrifugal force of that side of the earth,
which is farthest from this center of motion, round which the earth and
moon monthly revolve, is considerably greater, than the centrifugal force
of that side of the earth, which is nearest it; to which should be added,
that this centrifugal force not only contributes to diminish the terrene
gravitation of bodies on the earth's surface on that side furthest from
this center of motion, but also to increase it on that side, which is
nearest it.

Another circumstance, which tends to raise the tide on the part of the
earth's surface, which is most distant from the moon, is, that the
attraction of the moon is less on that part of the ocean, than it is on the
other parts of the earth. Thus the moon may be supposed to attract the
water on the side of the earth nearest it with a power equal to three; and
to attract the central parts of the earth with a power equal to two; and
the water on the part of the earth most distant from the moon with a power
only equal to one. Hence on the side of the earth most distant from the
moon, the moon's attraction is less, and the centrifugal force round their
common center of motion is greater; both which contribute to raise the
tides on that side of the earth. On the side of the earth nearest the moon,
the moon's attraction is so much greater as to raise the tides; though the
centrifugal force of the surface of the earth round their common center of
motion in some degree opposes this effect.

On these accounts, when the moon is in the zenith or nadir, the gravitation
of bodies on the earth's surface will be greatest at the two opposite
quadratures; that is, the greatest gravitation of bodies on the earth's
surface towards her center during the lunar day is about six hours and an
half after the southing, or after the northing of the moon.

Circumstances similar to these, but in a less degree, must occur in respect
to the solar influence on terrestrial bodies; that is, there must be a
diminution of the gravity of bodies, near the earth's surface at noon, when
the sun is over