to
the earth. To convince yourself of it, only imagine the earth 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 spher