An entire body of philosophy according to the principles of the famous Renate Des Cartes in three books, (I) the institution ... (II) the history of nature ... (III) a dissertation of the want of sense and knowledge in brute animals ... / written originally in Latin by the learned Anthony Le Grand ; now carefully translated from the last corrections, alterations, and large additions of the author, never yet published ... by Richard Blome.

CHAP. IX. Of the Planets, Mercury, Venus, Jupiter, and Saturn.

I. The Pla∣nets, Mer∣cury and Venus, seem to move va∣riously. MErcury and Venus appear sometimes to move from East to West; and at othertimes the contrary way, from West to East.

Forasmuch as the Earth is turn'd round about its Center from West to East, within the space of 24 hours, it follows that the Planets, Mercury and Venus must seem to move from East to West, and every day to describe a Circle Parallel to the Ae∣quator. In like manner they must also trace a Circle about the Sun from West to East; foras∣much as they are comprehended in the Heavenly matter, which carries the Earth that way.

II. Why the foresaid Planets are more swift∣ly carried about the Sun, than the Earth. These 2 Planets are also more swiftly rolled about the Sun, than the Earth, which doth not finish its Circumvolution in less than a Year.

The Reason is, because the Circles which Mer∣cury and Venus run through, about the Sun, are lesser than that in which the Earth is carried; and therefore it is necessary, that the true Circumvo∣lutions of these 2 Planets be absolved in less than a years time.

III. Why Mer∣cury and Venus seem to move more slow∣ly, than indeed they do. These 2 Planets seem to take up more time in their Circumvolution, than indeed they do.

The Reason is, because if we fix the beginning of one of their Revolutions, when these Planets are placed betwixt the Sun and the Moon, this Period cannot be said to be finished, till they be come back to the same place again. Now forasmuch as the Earth it self hath changed its place, whilst those Planets run through their Circles, and at the end of their circumvolution is no more at the same place where it was at the beginning of it; it fol∣lows that the appearing Period of every Planet, must of necessity comprehend, not only the whole Circumvolution it hath absolved; but besides all that space to which the Earth hath past through during the time of the Planets Circumvolution.

IV. Cassinus his Obser∣vations a∣bout the Planet Mercury. CASSINUS observes concerning the Pla∣net Mercury, that the same is scarcely visible, be∣cause of his great nearness to the Sun, so as that it but very seldom gets free of his Rays. For he is not above 27 or 28 degrees distant from the Sun, and often turns back to the Sun again, by that time he is got 18 degrees from him, so that his greatest elongations, from the Sun, do not dif∣fer above 9 degrees from each other.

The Circle of Mercuries Motion divides the Ecliptick; and with it makes an Angle of 6 de∣grees; so as that the line of Section, is not far from the Center of the Sun. The Northern Intersecti∣on, which some call the Node, is reduced to the 13th degree of Scorpio: and these Nodes proceed one degree within the space of 40 years.

Forasmuch therefore as Mercury doth not ap∣pear to us, but in his withdrawing from the Sun, he can scarcely be perceived with the help of a Telescope, in the form of a Globe or Round Body, but sometimes as if he were cut in 2, as the Moon ap∣pears at her Quarters; and sometimes more swell'd, and at others more deprest. And when at any time he is near the Horizon, or darkned with va∣pours, then nothing but his Bulk or Figure can be detected. However it is apparent that he receives his Light from the Sun, and is carried round him.

V. Cassinus his Obser∣vations about the Planet Ve∣nus. Concerning the Planet Venus, the foresaid Cas∣sinus hath observed; first that this Planet is some∣times 40 degrees and an half distant from the Sun, that is, as far as the Moon at 4 days old is di∣stant from him. Tho' sometimes it happens that she returns to the Sun, after a recess from him to 45 degrees; so as that the furthest elongations of this Planet do not differ above 2 degrees.

The Aphelium, or farthest distance of Venus from the Sun, is in the 2d degree of Aquarius; her Perihelium, or nearest approximation in the 2d of Taurus: and these Points do continually move onwards towards the East, so as that within the space of 46 years, they proceed one degree.

The foresaid famous man found that these 2 Planets moved about their own Centers. For when in the year 1666, he had observed one part of Venus to be brighter than all the other parts of her Circumference, on the 14th of Octo∣ber, 5 hours and 15 minutes after Noon; and the year following on the 24th day of April, about a quarter of an hour before Sun-set, had found the same bright part, near to the Line which separates the Lucid part of Venus from the Opake, and di∣stant from her Southern Horn, above a quarter of the Diameter of Venus: and when after Sun-rising he had observed that the said Bright Part was fur∣ther removed from the Southern Horn, from which it was distant the 3d part of her Diameter; he immediately concluded, that some kind of motion, at least, must be assigned to the Globe of Venus, tho' he dares not determine whether▪ the same be a motion of Rotation, or of Libration only: Be∣cause Venus doth not present her self to her view but for a short time. But supposing that bright part, which he had so often seen, to have been always the same, he is not afraid to affirm that the said motion is finisht in about 23 hours; after which the said bright part of Venus returns again to the same place.

[illustration]

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Book. 2. Part. 3. Chap. 9.

〈1 line〉〈1 line〉

I. Kip▪ 〈◊〉〈◊〉

To M^r. Edward, M^r. Nicholas, M^is. Ann, M^is. Iane, and M^is. Sarah Ieffreys, Sons and Daughters of the Worshipfull Ieffrey Ieffreys of the Priory in Brecknock∣shire and of the Citty of London Esq^r, by Sarah his Wife.

This Plate is humbly Dedicated by Richard Blome.

VI. Why Mars, Jupiter, and Saturn do une∣qually ob∣serve their Course. Mars, Jupiter, and Saturn, seem to roll about like other Planets, within the space of 24 Hours, from East to West about the Earth; but not equally within the same term of Time.

The Reason is, because the Circles they describe do include the Circle of the Earth, and because they, as well as the Earth, do swim in the Celestial matter; and consequently must appear, as the other Planets, to turn from East to West, within the space of 24 Hours. And forasmuch as, ac∣cording to the Law of Mechanicks, the Circles which Mars, Jupiter, and Saturn do describe, must be found under the Zodiack, and are greater than that which the Earth moves in, we shall easily apprehend, that they cannot finish their Circuit in so short a time as it doth. Accordingly we know, that Mars takes up 2 years in performing his Circumvolution, Jupiter 12, and Saturn 30; for they being at a farther distance from the Sun, than the Earth, the Heavenly matter which carries them about, must take up the same time in absolving of its Course.

VII. Cassinus, his Obser∣vations concerning Mars. CASSINUS also gathers from those spots, that obscure the Aspect of Mars, that this Planet moves about his own Center, in the space of 24 Hours and 40 Minutes, because these spots return to the same place, at the same distance of time. He observed in Mars one part more bright than all the rest, and always in the same situation; tho' the other spots had their different places.

Jupiter, when he is in Conjunction with the Sun, appears at a greater distance to us, than when he is in opposition to him; insomuch that we see him almost bigger by one half, when he is op∣pos'd to the Sun, than when conjoyn'd with him. And Mars appears five-fold greater, when he is nearest to the Earth, than when he is at his fur∣thest Elongation from it.

VIII. The secon∣dary Pla∣nets about Jupiter, first disco∣ver'd by Galilaeus. GALILAEUS, in the year 1610, the 7th of January, at the first Hour of the Night, dis∣covered 4 less Planets about Jupiter, which like so many little Moons are whirl'd round him. Those of them which are nearest to Jupiter, move more swiftly, than those which are more remote. The Revolutions of which secondary Planets are thus calculated by SIMON MA∣RIUS:

The first and inmost of them takes up,

• D. 1
• H. 18
• M. 28
• S. 30

The Second.

• D. 03
• H. 13
• M. 18
• S. 0

The Third

• D. 7
• H. 03
• M. 56
• S. 34

The Fourth.

• D. 16
• H. 18
• M. 09
• S. 15

These Attendants of Jupiter, whenever they enter the Verge of his shadow, do suffer an Eclipse after the same manner, as the Moon doth when she dips in the shadow of the Earth, and are totally depriv'd of Light; as being Opake Bodies, which borrow their Light from the Sun. The 3 first of these in every Revolution, produce 4 Eclipses; the 1st, when the Satelles enters into the Rim of Jupiter; the 2d, when the shadow of the Satelles doth darken the Rim of the said Planet; the 3d, when the upper part of Jupiter, at his Elongation from us▪ doth hide the Satelles▪ and the 4th, when the Satelles dips in the shadow of Jupiter: So as that the first Satelles, within the space of 7 Days, doth effect 16 Eclipses; the second, 8; the third, 4; so as that all of them together produce 28 Eclipses: The fourth, after that he hath reached the Nodes, doth make 4 Eclipses in 17 days; but when near his bounds, he never suffers a defect of his Light, because his Latitude is so large, that he never touches the Rim of Jupiter, or reacheth his shadow. These Eclipses are of great use, in order to the deter∣mining of the Longitudes of Places.

IX. The Satel∣lites of Saturn, discover'd by Cassinus and Huge∣nius. Saturn hath also been found guarded by 3 Satel∣lites: The first of these was discovered by CASSINUS, at Paris, in the Royal Observa∣tory, in the Year 1672; and the same is remov'd from the Center of Saturn, 1 Diameter of the Ring, (mention'd by the Author, Chap. 16.) and 2 Thirds, and absolves his motion about the Pla∣net in 12 Days, 4 Hours, and 27 Minutes. The second was long before detected by HUGE∣NIUS, and is much more bright than the for∣mer; and is distant from the Center of Saturn, 4 Diameters of the said Ring, and turns round him within the space of 16 Days and 23 Hours. The third was first observed by CASSINUS, in the year 1671, towards the End of October, at his furthest digression from Saturn. But soon after he vanish'd out of sight, and did not appear again till the 15th of December; and presently after disappeared, until about the beginning of February 1673, when he continued in sight for 13 Days together.

X. What is the Cause of the variation of Light, which is observed in the last Satelles of Saturn. No other Reason seems assignable for this great variation of Light in this last Satelles, than that some part of his Body doth strongly reflect the Light, whereas the other cannot do so. According as we see it happens in the Globe of Earth, where that part which is cover'd with water, is not fit to reflect the Sun-beams; where∣as the other parts of it send them back every way. This Satelles therefore either i•• rolled about his own Center, or else is carried about Saturn▪ as the Moon is carried about the Earth. And there∣fore when that par•• of him, which is like the Con∣tinent of our Earth is turned towards us, then we see him, and he vanisheth again from our ••ight, when that part which is of the Nature o•• Sea, faceth the Earth.

XI. Why Sa∣turn ap∣pears un∣der diffe∣rent figures. They who first observed Saturn with a short and imperfect Telescope, were astonished when they perceived him sometimes of an Oval figure, sometimes as having 3 Bodies, that is, with •• other added to the middlemost; sometimes solitary and perfectly round. But when these unlook'd for Appearances had stirr'd up others to the view∣ing of this Planet, some making use of more exquisite Instruments, ••ound, that those which before were taken to be the Lateral Globes, were in the figure of Handles or Arms, that is, hol∣lowed out and bent, so that joyned to the middle Globe, they constituted a figure not unlike a Weavers▪shuttle. But at last, by the use of the most absolute Telescopes, it was ••ound that this Planet hath a round Body, as all the rest; but hath this peculiar, that it is encompas••, as it were, with a broad Ring, not much unlike the Brim of a Hat, when the Head i•• out of it; or that of a

Dish, when the bottom or hollow is taken away. And therefore this ambient Body, which before was called the Handle or Arms of Saturn, was since called the Ring.

In order to the explaining of this Appearance, we must represent to our selves this Planet, as a great Globe, resembling that of the Earth, and in which we conceive 2 Poles, an Equator, and a Torrid Zone; and that round about the said Torrid Zone there is elevated an opake Matter, which fills the space of a considerable breadth, and is disposed in the figure of a Ring, resembling that broad Circle we call the Horizon. This being thus supposed, it is certain that we must of neces∣sity see Saturn, according as he appears at A, when we view him from a place that is much higher than the Level of the Ring; afterwards he must appear to us, as at B, or at C, when we * 1.1behold him from a place where we are not so high as the said Level. And last of all he must appear altogether round to us, as at D, when we are so placed with respect to his Body, that if his Ring were continued, it would pass through our Eye; for then the inconsiderableness of the Thickness it hath, by reason of its great distance, makes it altogether invisible. To which may be added, that probably we fail of seeing this Ring of Sa∣turn, because this Planet passing over against some fixt Star, and having deprived us of the view of it by one of the Tops of the Oval G, in the Figure A, the said Star will afterwards be seen at the place E, where we see a kind of Blackness, which is nothing else but the defect of the Circle, and a part of the Heaven, which offers it self to our view, by that space which remains betwixt the said Ring and Body of Saturn.

Notes

• * 1.1

  Figure 15.