Astronomy Explained Upon Sir Isaac Newton's Principles: And made easy to those who have not studied mathematicsFerguson, James
Science
Astronomy Explained Upon Sir Isaac Newton's Principles: And made easy to those who have not studied mathematics
Ferguson, James
Astronomy -- Early works to 1800
268. The Moon’s path being concave to the Sun throughout, demonstrates
that her gravity towards the Sun, at her conjunction, exceeds her
gravity towards the Earth. And if we consider that the quantity of
matter in the Sun is almost 230 thousand times as great as the quantity
of matter in the Earth, and that the attraction of each body diminishes
as the square of the distance from it increases, we shall soon find,
that the point of equal attraction where these two powers would be
equally strong, is about 70 thousand miles nearer the Earth than the
Moon is at her Change. It may now appear surprising that the Moon does
not abandon the Earth when she is between it and the Sun, because she is
considerably more attracted by the Sun than by the Earth at that time.
But this difficulty vanishes when we consider, that the Moon is so near
the Earth in proportion to the Earth’s distance from the Sun, that she
is but very little more attracted by the Sun at that time than the Earth
is; and whilst the Earth’s attraction is greater upon the Moon than the
difference of the Sun’s attraction upon the Earth and her (and that it
is always much greater is demonstrable) there is no danger of the Moon’s
leaving the Earth; for if she should fall towards the Sun, the Earth
would follow her almost with equal speed. The absolute attraction of the
Earth upon a drop of falling rain is much greater than the absolute
attraction of the particles of that drop upon each other, or of it’s
center upon all parts of it’s circumference; but then the side of the
drop next the Earth is attracted with so very little more force than
it’s center, or even it’s opposite side; that the attraction of the
center of the drop upon it’s side next the Earth is much greater than
the difference of force by which the Earth attracts it’s nearer surface
and center: on which account the drop preserves it’s round figure, and
might be projected about the Earth by a strong circulating wind so as to
be kept from falling to the Earth. It is much the same with the Earth
and Moon in respect to the Sun; for if we should suppose the Moon’s
Orbit to be filled with a fluid Globe, of which all the parts would be
attracted towards the Earth in it’s center, but the whole of it much
more attracted by the Sun; one part of it could not fall to the Sun
without the other, and a sufficient projectile force would carry the
whole fluid Globe round the Sun. A ship, at the distance of the Moon,
sailing round the Earth on the surface of the fluid Globe, could no more
be taken away by the Sun when it is on the side next him, than the Earth
could be taken away from it when it is on the opposite side; which could
never happen unless the Earth’s projectile motion were stopt; and if it
were stopt, the Ship with the whole fluid Globe, Earth and all together,
would as naturally fall to the Sun as a drop of rain in calm air falls
to the Earth. Hence we may see, that the Earth is in no more danger of
Public-domain text, read in full here on John Shaqi.
Reviews
Reviews
No reviews yet
Be the first to share your thoughts on this work.
Elsewhere in the archive
Join the Discussion
Join the discussion
Sign in to leave a comment or review.
Sign InorCreate an account