Читать книгу The Natural History of Pliny (Vol. 1-6) - Pliny the Elder - Страница 21

Table of Contents

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 apsides213, 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 world214; 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 compasses215. 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 earth216. 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 above217. 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 air218. With this cause is connected that which depends on the latitude of the planets and the obliquity of the zodiac. It is through this belt that the stars which I have spoken of are carried, nor is there any part of the world habitable, except what lies under it219; the remainder, which is at the poles, being in a wild desert state. The planet Venus alone exceeds it by 2 degrees, which we may suppose to be the cause why some animals are produced even in these desert regions of the earth. The moon also wanders the whole breadth of the zodiac, but never exceeds it. Next to these the planet Mercury moves through the greatest space; yet out of the 12 degrees (for there are so many degrees of latitude in the zodiac220), it does not pass through more than 8, nor does it go equally through these, 2 of them being in the middle of the zodiac, 4 in the upper part, and 2 in the lower part221. Next to these the Sun is carried through the middle of the zodiac, winding unequally through the two parts of his tortuous circuit222. The star Mars occupies the four middle degrees; Jupiter the middle degree and the two above it; Saturn, like the sun, occupies two223. The above is an account of the latitudes as they descend to the south or ascend to the north224. Hence it is plain that the generality of persons are mistaken in supposing the third cause of the apparent altitude to depend on the stars rising from the earth and climbing up the heavens. But to refute this opinion it is necessary to consider the subject with very great minuteness, and to embrace all the causes.

It is generally admitted, that the stars225, at the time of their evening setting, are nearest to the earth, both with respect to latitude and altitude226, that they are at the commencement of both at their morning risings, and that they become stationary at the middle points of their latitudes, what are called the ecliptics227. It is, moreover, acknowledged, that their motion is increased when they are in the vicinity of the earth, and diminished when they are removed to a greater altitude228; a point which is most clearly proved by the different altitudes of the moon. There is no doubt that it is also increased at the morning risings229, and that the three superior planets are retarded, as they advance from the first station to the second. And since this is the case, it is evident, that the latitudes are increased from the time of their morning risings, since the motions afterwards appear to receive less addition; but they gain their altitude in the first station, since the rate of their motion then begins to diminish230, and the stars to recede.

And the reason of this must be particularly set forth. When the planets are struck by the rays of the sun, in the situation which I have described, i. e. in their quadrature, they are prevented from holding on their straight forward course, and are raised on high by the force of the fire231. This cannot be immediately perceived by the eye, and therefore they seem to be stationary, and hence the term station is derived. Afterwards the violence of the rays increases, and the vapour being beaten back forces them to recede.

This exists in a greater degree in their evening risings, the sun being then turned entirely from them, when they are drawn into the highest apsides; and they are then the least visible, since they are at their greatest altitude and are carried along with the least motion, as much less indeed as this takes place in the highest signs of the apsides. At the time of the evening rising the latitude decreases and becomes less as the motion is diminished, and it does not increase again until they arrive at the second station, when the altitude is also diminished; the sun’s rays then coming from the other side, the same force now therefore propels them towards the earth which before raised them into the heavens, from their former triangular aspect232. So different is the effect whether the rays strike the planets from below or come to them from above. And all these circumstances produce much more effect when they occur in the evening setting. This is the doctrine of the superior planets; that of the others is more difficult, and has never been laid down by any one before me233.