t a brief
explanation of the grounds upon which astronomers are as universally
agreed upon the belief of the sun's motion around a center of the
firmament, as they are upon the belief of the revolution of the earth
round the sun.

When you are passing in a carriage, at night, through the street of a
city lighted up by gas-lamps in the streets, and lights irregularly
dispersed in the windows, or passing in a ferry-boat, from one such city
to another, at a short distance from it, you observe that the lights
which you are leaving appear to draw closer and closer together, while
those toward which you are approaching widen out, and seem to separate
from each other. If the night were perfectly dark, so that you could see
nothing but the lights, you could certainly know not only that you were
in motion, but also to what point you were moving, by carefully watching
their appearances. So, if all the fixed stars were absolutely fixed, and
the sun and planets, including our earth, were moving in any
direction--say to the north--then the stars toward which we were moving
would seem to widen out from each other, and those which we were
leaving would seem to close up; so that the space which appeared between
any two stars in the south, in a correct map of the heavens, a hundred
years ago, would be smaller, and that between any two stars in the north
would be larger, than the space between the same stars upon a correct
map now. Now, such changes in the apparent positions of stars are
actually observed. The stars do not appear in the same places now as
they did a hundred years ago.

The fixed stars, then, are either drifting past our solar system, which
alone remains fixed; or, the fixed stars are all actually at rest, and
our sun is drifting through them; or, our solar system and the so-called
fixed stars are both in motion. One or other of these suppositions must
be the fact. The first is simply the old Ptolemaic absurdity, only
transferring the center of the universe to the sun. The second is
contrary to the observed fact, that multitudes of the stars, which were
supposed to be fixed, are actually revolving around each other, in
systems of double, triple and multiple suns. And both are contrary to
the first principles of gravitation; for, as every particle of matter
attracts every other, directly as the mass, and inversely as the square
of the distance, if any one particle of matter in the universe is in
motion, the square of its