out of existence. There would then be no rising and setting of
the sun or of the moon, no horizon, no meridian, no day, no
night--in short, the said motion causes no change of any sort in
the relation of the sun to the moon or to any of the other
heavenly bodies, be they planets or fixed stars. All changes are
rather in respect to the earth; they may all be reduced to the
simple fact that the sun is first visible in China, then in
Persia, afterwards in Egypt, Greece, France, Spain, America,
etc., and that the same thing happens with the moon and the other
heavenly bodies. Exactly the same thing happens and in exactly
the same way if, instead of disturbing so large a part of the
universe, you let the earth revolve about itself. The difficulty
is, however, doubled, inasmuch as a second very important problem
presents itself. If, namely, that powerful motion is ascribed to
the heavens, it is absolutely necessary to regard it as opposed
to the individual motion of all the planets, every one of which
indubitably has its own very leisurely and moderate movement from
west to east. If, on the other hand, you let the earth move about
itself, this opposition of motion disappears.
"The improbability is tripled by the complete overthrow of that
order which rules all the heavenly bodies in which the revolving
motion is definitely established. The greater the sphere is in
such a case, so much longer is the time required for its
revolution; the smaller the sphere the shorter the time. Saturn,
whose orbit surpasses those of all the planets in size, traverses
it in thirty years. Jupiter[4] completes its smaller course in
twelve years, Mars in two; the moon performs its much smaller
revolution within a month. Just as clearly in the Medicean stars,
we see that the one nearest Jupiter completes its revolution in a
very short time--about forty-two hours; the next in about three
and one-half days, the third in seven, and the most distant one
in sixteen days. This rule, which is followed throughout, will
still remain if we ascribe the twenty-four-hourly motion to a
rotation of the earth. If, however, the earth is left motionless,
we must go first from the very short rule of the moon to ever
greater ones--to the two-yearly rule of Mars, from that to the
twelve-yearly one of Jupiter, from here to the thirty-yearly one
of Saturn, and then suddenly to an incomparably greater sphere,
to which also we must ascribe a complete rotation in twenty-four
hours. If, however, we assume a motion of the earth, the rapidity
of the periods is very well preserved; from the slowest sphere of
Saturn we come to the wholly motionless fixed stars. We also
escape thereby a fourth difficulty, which arises as soon as we
assume that there is motion in the sphere of the stars. I mean
the great unevenness in the movement of these very stars, some of
which would have to revolve with extraordinary rapidity in
immense circles, while others moved very slowly in small circles,
since some of them are at a greater, others at a less, distance
from the pole. That is likewise an inconvenience, for, on the one
hand, we see all those stars, the motion of which is indubitable,
revolve in great circles, while, on the other hand, there seems
to be little object in placing bodies, which are to move in
circles, at an enormous distance from the centre and then let
them move in very small circles. And not only are the size of the
different circles and therewith the rapidity of the movement very
different in the different fixed stars, but the same stars also