§ 52b. When by the singular strength of his Genius, (which he exerted in
the finding out such a Demonstration) he had satisfied himself that the
Body of Heaven was finite; he desired, in the next place, to know what
Figure it was of, and how it was limited by the circumambient
Superficies. And first he observ'd the Sun, Moon and Stars, and saw that
they all rose in the East, and set in the West; and those which went
right over his Head describ'd a great Circle, but those at at greater
distance from the Vertical Point, either Northward or Southward,
describ'd a lesser Circle. So that the least Circles which were
describ'd by any of the Stars, were those two which went round the two
Poles, the one North, the other South; the last of which is the Circle
of _Sohail_ or _Canopus_; the first, the Circle of those two Stars which
are called in _Arabick Alpherkadâni_. Now because he liv'd under the
Equinoctial Line, (as we shew'd before) all those Circles did cut the
Horizon at right Angles, and both North and South were alike to him, and
he could see both the Pole-Stars: He observ'd, that if a Star arose at
any time in a great Circle, and another Star at the same in a lesser
Circle, yet nevertheless, as they rose together, so they set together:
and he observ'd it of all the Stars, and at all times. From whence he
concluded, that the Heaven was of a Spherical Figure; in which Opinion
he was confirm'd, by observing the Return of the Sun, Moon and Stars to
the East, after their Setting; and also, because they always appear'd to
him of the same bigness, both when they rose, and when they were in the
midst of Heaven, and at the time of their Setting; whereas, if their
Motions had not been Circular, they must have been nearer to sight, at
some times than others; and consequently their Dimensions would have
appear'd proportionably greater or lesser; but since there was no such
Appearance, he concluded that their Motions were Circular. Then he
consider'd the Motion of the Moon and the Planets from West to East,