CHAP. 13.—WHY THE SAME STARS APPEAR AT SOME TIMES MORE LOFTY AND AT OTHER TIMES MORE NEAR. The above is an account of the aspects and the occultations of the planets, a subject which is rendered very complicated by their motions, and is involved in much that is wonderful; especially, when we observe that they change their size and colour, and that the same stars at one time approach the north, and then go to the south, and are now seen near the earth, and then suddenly approach the heavens. If on this subject I deliver opinions different from my predecessors, I acknowledge that I am indebted for them to those individuals who first pointed out to us the proper mode of inquiry; let no one then ever despair of benefiting future ages. But these things depend upon many different causes. The first cause is the nature of the circles described by the stars, which the Greeks term _apsides_[213], for we are obliged to use Greek terms. Now each of the planets has its own circle, and this a different one from that of the world[214]; because the earth is placed in the centre of the heavens, with respect to the two extremities, which are called the poles, and also in 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[215]. 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 Jupiter in Virgo, for Mars in Leo, for the Sun in Gemini, 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[216]. 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[217]. 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.