them; and also at midnight from the greater centrifugal
force of that side of the earth, which is most distant from the center,
round which the earth moves in her annual orbit, than on the side nearest
that center. Whence it likewise follows, that the gravitation of bodies
towards the earth is greatest about six hours after noon, and after
midnight.

Now when the sun and moon have their united gravitation on the same side of
the earth, as at the new moon; or when the solar attraction coincides with
the greater centrifugal motion of that side of the earth, which is furthest
distant from the moon, as at the full moon; and when this happens about
noon or midnight, the gravitation of terrene bodies towards the earth will
be greater about six hours after noon, and after midnight, than at any
other part of the lunar period; because the attraction of both these
luminaries is then exerted on those sides of the earth over which they
hang, which at other times of the month are more or less exerted on other
parts of it.

Lastly, as heat and motion counteract the gravitation of the particles of
bodies to each other, and hence become either the efficient causes of
vegetable and animal life, or the causes without which life cannot exist,
it seems to follow, that when our gravitation towards the earth's center is
greatest, the powers of life should be the least; and hence that those
diseases, which begin with torpor, should occur about six hours after the
solar or lunar noon, or about six hours after the solar or lunar midnight;
and this most frequently about six hours after or before the new or full
moon; and especially when these happen at noon or at midnight; or lastly,
according to the combination of these powers in diminishing or increasing
the earth's attraction to bodies on its surface.

The returns or exacerbations of many fevers, both irritative and
inflammatory, about six in the evening, and of the periodic cough described
in Sect. XXXVI. 3. 9. countenance this theory. Tables might be made out to
shew the combined powers of the sun and moon in diminishing the gravitation
of bodies on the earth's surface, at every part of their diurnal, monthly,
and annual periods; and which might facilitate the elucidation of this
subject. But I am well aware of the difficulty of its application to
diseases, and hope these conjectures may induce others to publish more
numerous observations, and more conclusive reasonings.

SPECIES.

1.