Chap. 13.] 
ACCOITKT OF THE WOIILD 
43 
that of the zodiac, which is situated obliquely between them. 
And all these things are made evident by the infallible results 
which we obtain by the use of the compasses \ Hence the 
apsides of the planets have each of them different centres, and 
consequently they have different orbits and motions, since it 
necessarily follows, that the interior apsides are the shortest. 
(16.) The apsides which are the highest from the centre 
of the earth are, for Saturn, when he is in Scorpio, for J upiter 
in Virgo, for Mars in Leo, for the Sun in Gremini, for Venus 
in Sagittarius, and for Mercury in Capricorn, each of them 
in the middle of these signs; while in the opposite signs, 
they are the lowest and nearest to the centre of the earth^. 
Hence it is that they appear to move more slowly when 
they are carried along the highest circuit ; not that their 
actual motions are accelerated or retarded, these being fixed 
and determinate for each of them ; but because it necessarily 
follows, that lines drawn from the highest apsis must approach 
nearer to each other at the centre, like the spokes of a wheel ; 
and that the same motion seems to be at one time greater, 
and at another time less, according to the distance from the 
centre. 
Another cause of the altitudes of the planets is, that their 
highest apsides, with relation to their own centres, are in 
different signs from those mentioned above^. Saturn is in 
the 20th degree of Libra, Jupiter in the 15th of Cancer, 
Mars in the 28th of Capricorn, the Sun in the 19th of Aries, 
Venus in the 27th of Pisces, Mercury in the 15th of Virgo, 
and the Moon in the 3rd of Taurus. 
The third cause of the altitude depends on the form of the 
heavens, not on that of the orbits ; the stars appearing to 
the eye to mount up and to descend through the depth of 
the air"*. "With this cause is connected that which depends 
^ " ratione circini semper indubitata." 
2 In consequence of the precession of the equinoxes these points are 
continually advancing from W. to E., and are now about 30 degrees from 
the situation they were in when the observations were first made by 
the modern astronomers. 
^ Our author here probably refers to the motions of the planets through 
their epicycles or secondary circles, the centres of which were supposed 
to be in the peripheries of the primary circles. See Alexandre in Le- 
maire, ii. 270. 
^ It is to this visible appearance of convexity in the heavens that Ovid 
