the earth stands between them and the sun--but that they are
farthest from the earth when they set in the evening--that is,
when we have the sun between them and the earth. This proves
sufficiently that their centre belongs to the sun and is the same
about which the orbits of Venus and Mercury circle. Since,
however, all have one centre, it is necessary for the space
intervening between the orbits of Venus and Mars to include the
earth with her accompanying moon and all that is beneath the
moon; for the moon, which stands unquestionably nearest the
earth, can in no way be separated from her, especially as there
is sufficient room for the moon in the aforesaid space. Hence we
do not hesitate to claim that the whole system, which includes
the moon with the earth for its centre, makes the round of that
great circle between the planets, in yearly motion about the sun,
and revolves about the centre of the universe, in which the sun
rests motionless, and that all which looks like motion in the sun
is explained by the motion of the earth. The extent of the
universe, however, is so great that, whereas the distance of the
earth from the sun is considerable in comparison with the size of
the other planetary orbits, it disappears when compared with the
sphere of the fixed stars. I hold this to be more easily
comprehensible than when the mind is confused by an almost
endless number of circles, which is necessarily the case with
those who keep the earth in the middle of the universe. Although
this may appear incomprehensible and contrary to the opinion of
many, I shall, if God wills, make it clearer than the sun, at
least to those who are not ignorant of mathematics.

"The order of the spheres is as follows: The first and lightest
of all the spheres is that of the fixed stars, which includes