Thebit, with the
view of {237} laying down a rule for such considerable inequalities in the
motion of the stars, explained that the eighth sphaere does not move with a
continuous motion from west to east; but is shaken with a certain motion of
trepidation, by which the first points of Aries and Libra in the eighth
heaven describe certain small circles with diameters equal to about nine
degrees, around the first points of Aries and Libra in the ninth sphaere.
But since many things absurd and impossible as to motion follow from this
motion of trepidation, that theory of motion is therefore long since
obsolete. Others therefore are compelled to attribute the motion to the
eighth sphaere, and to erect above it a ninth heaven also, yea, and to pile
up yet a tenth and an eleventh: In the case of mathematicians, indeed, the
fault may be condoned; for it is permissible for them, in the case of
difficult motions, to lay down some rule and law of equality by any
hypotheses. But by no means can such enormous and monstrous celestial
structures be accepted by philosophers. And yet here one may see how hard
to please are those who do not allow any motion to one very small body, the
Earth; and notwithstanding they drive and rotate the heavens, which are
huge and immense above all conception and imagination: I declare that they
feign the heavens to be three (the most monstrous of all things in Nature)
in order that some obscure motions forsooth[251] may be accounted for.
Ptolemy, who compares with his own the observations of Timocharis and
Hipparchus, one of whom flourished 260 years, the other 460 years before
him, thought that there was this motion of the eighth sphaere, and of the
whole firmament; and proved by help of numerous phenomena that it took
place over the poles of the Zodiack, and, supposing its motion to be so far
aequable, that the non-planetary stars in the space of 100 years completed
just one degree beneath the _Primum Mobile_. After him 750 years
Albategnius discovered that one degree was completed in a space of 66
years, so that a whole period would be 23,760 years. Alphonsus made out
that this motion was still slower, completing one degree and 28 minutes
only in 200 years; and that thus the course of the fixed stars went on,
though unequally. At length Copernicus, by means of the observations of
Timocharis, Aristarchus of Samos, Hipparchus, Menelaus, Ptolemy, Mahometes
Aractensis, Alphonsus, and of his own, detected t