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. XII. Of Comets.

I. Comets run through several Regions of the Hea∣vens. COmets observe no certain Tract in the Hea∣vens, but perform their Courses sometimes through this, and sometimes through another part of them. For some do first appear at the Sun's rising, others at his setting. The Comet which appeared in the Year 1585, was almost directly opposite to the Sun, and wanted but little of receiving his Rays directly: Whereas another that appeared in 1607, was first seen about the Bear, when the Sun was near the Winter Tro∣pick.

The Cause of these Appearances will be evi∣dent to us, if we consider that Comets, are Stars cover'd with spots, and swallowed up of other Vortexes. Now, forasmuch as they may happen to fall into any Quarter of the Heavens, accordingly they may sometimes pass through one, and at other times through another part of the Heaven; neither is there any part through which they may not take their course at some time or other. The place therefore of the appearance of Comets, is very uncertain, seeing that they promiscuously may pass by the Stars of any Asterism. So that Comet which appeared in 1618, did seem to come forth from the Rays of the Rising-Sun; when as others have been seen to appear from under the Beams of the Setting-Sun.

II. Why some Comets move to∣wards the East, others towards the West. Comets seem to move every day, from East to West about the Earth; because the Earth moves the quite contrary way. But yet forasmuch as their own proper motion is indeterminate, those which come from a Vortex, which is towards the East, supposing they can continue their motion, will move towards the West; and those which proceed from a Vortex towards the West, must consequently move twards the East; yet with this Circumstance, that when they have once taken their determination towards the East, or towards the West, their Course is every whit as exact as that of the Planets; for after having 2 or 3 times calculated their Diurnal motion, it is easie to com∣pose an Ephemerides of their whole Course, and to know as perfectly the degrees of their swiftness and slowness, as we know all the degrees of Heaven, through which they are to take their progress, and their various Configurations with the Stars.

III. Why the Comets vanish at last. From what hath been said, may be gather'd the Reason why a Comet at first appears greater, and afterwards continually decreaseth, until its total disappearance: For seeing that Comets receive their Light from the Sun, after that they are past out of our Vortex, they can no longer appear to our Eyes.

IV. The Time of the Continu∣ance of Comets, is uncertain. Comets have no time prefixt to their motion: For sometimes many years pass without the appearance of any of them; and at other times many are seen in one and the same year: As Historians tell us, that in the year 1618, there appeared no less than 3 or 4.

Forasmuch as Comets proceed from several Vor∣texes into ours, it is very difficult to determine, whether their Appearance be fortuitous and casual, or regulated and necessary: But howsoever it be, we are to consider it as fortuitous, because all the Observations that have be been made hitherto about this Matter, are not over exact. And if so be that Comets do never begin to appear in the Zodiack, it is without doubt, because the motion of our Vortex, which is very rapid in that part of it, makes their entrance that way more difficult, or, it it may be, altogether impossible.

V. Why Co∣mets do generally appear under the same Mag∣nitude. Comets do generally appear under the same Magnitude, insomuch as that being beheld through a Telescope (if we will believe the Assertions of some) they do not appear greater, than when beheld without it.

The Reason is, because they are so far from us, that one and the same Comet may be perceived at the same time by several Spectators, tho' at a vast distance from one another, and that without any Parallax. So that they are probably concluded to be in that vast Space which is supposed to be betwixt Saturn and the fixt Stars. For the Comets are such vast Bodies, and are moved with such extraordinary swiftness, that they stand in need of that immense Space for the performing of their Courses; neither can any other places be assigned, wherein they can conveniently absolve them.

VI. Comets being in the highest Heavens, cannot have any Parallax. But how can it be, may some say, That Comets being beheld by Spectators with a vast Tract of the Earth between them, should exhibit no Paral∣lax or variation of Aspect? This difficulty will be fully cleared by the Figure. For suppose we that some Luminous Body A, or F, placed in the lower part of Heaven, should be beheld by 2 Persons at a distance, D and B, at the same time; then will the Luminous Body A, which is seen by the Spectator D, appear over against the Luminous Body E; and the Luminous Body F, seen by the * 1.1other, will appear over against the Luminous Body H. But the same Luminous Body A, when per∣ceived by another Person at a distance B, will appear to him about the Luminous Body C. And the Luminous Body E, seen at the same time by the Person B, will be discover'd by him over against the Body G. And thus the Aspects of these 2 Bodies, A and F, according to their different situation, will produce a greater or less Parallax, as is C and E, or G and H. But if the Luminous Body be placed in the upper part of Heaven, about I; it will appear to both Persons, at a distance from each other, in the same place, that is, over against the Luminous Body K.

VII. Why the Comets do vanish after a few Months appearance. Comets, after a few Months or Days, do disappear and vanish. And therefore PLINY determines their longest appearance to 185 Days: Seeing that which was seen in Nero's time, and was lookt to be of the longest continuance of any other, was conspicuous only the time of 6 Months, tho' in all that time it scarce run through the one half of Heaven.

The Reason whereof is, because Comets, by passing from one Vortex to another, are driven to∣wards the Circumference of them, because of their solidity: And tho' they every where retain the same degree of Celerity; yet because they have more Agitation, than to be stopt by the Matter of the Vortex, through which they pass, they slip into a Neighbouring Vortex, much like a Ship, which being carried contrary to the Stream of a River, doth in some degree comply with the motion of the River, but is at last driven to the Shoar.

Thus a Comet Coursing it sometimes through this, and sometimes through another part of Heaven, doth continually keep it self at a distance from the Center of the Heaven, wan∣dering only in the Circumference of it; and so by this means it comes to leave our Heaven within a few Days or Months, and pass into others which are invisible to us. Wherefore, if we mea∣sure the Space which the Comets run through, we shall seldom perceive it to reach the half of a Circle, and that most frequently it doth not ex∣ceed the quarter of one. And if at any time it hap∣pens, that their Appearance is continued 4 Months, or longer, this is because they enter into our Vortex, near the Poles of it, where they find the Matter less agitated.

VIII. Comets move much more slowly towards the End of their Course, than at the begin∣ning of it. Comets about the beginning of their Appear∣ance are most swiftly moved, and but slowly to∣wards the end of it; according to the account which Astronomers give us of that which ap∣peared in 1572; which at the beginning of its motion, proceeded 5 Degrees every day, and to∣wards the End thereof scarcely Half a De∣gree.

The Reason hereof must be fetched from the distance of the Comets; for tho' Comets by pas∣sing through the Extremities or utmost parts of the Vortexes, do always keep the same degree of swiftness; yet because at first they have run a good way of their Course before we see them, by reason of the Matter they bring along with them, which too much refracts the Rays of Light; and then do by little and little move towards other Vortexes, and withdraw from our sight, therefore their Courses appear more slow towards the end of them. After the same manner as when we see a Traveller, passing on his way with the same pace, as long as he is not at any considerable distance from us, we perceive no difference in his gate, until he be come to a greater distance, when he appears to us to move more slowly; not because of his moving so indeed, but because of his greater distance from us.

IX. The Motion of Comets appears swifter in the middle of their motion. Tho' Comets move more swiftly, when they first enter into any Vortex, than after that they have been there for some time; yet is the midst of their Course swifter than any other parts of it; because being then in their Perigaeum, or place nearest to the Earth, they are also in those parts of the Line they describe, which are nearest to the Earth: Whereas, when they are at the beginning or end of their Course, they are about those parts of the same Line, which are the most remote from us. To this we must add, that when a Comet at the same time is in his Perigaeum, and his opposition with the Sun, his motion must appear much more swift, because he is then nearer to us by the whole quantity of the Excentrick of the Earth.

X. What is the Cause of the Tail and Beard of Comets. Comets commonly shed Hairs from them, especially on that side which is opposite to the Sun: But after a various manner; for some drag a Tail after them, others have a long Beard, others represent a Rose, by having these Hairs scatter'd round them.

This variety proceeds from the different Hea∣venly Globuli, that are found in our Heaven. For we suppose those that are near to the Center of our Vortex to be less, but that they increase by degrees, as they draw nearer to the Orb of Sa∣turn; which after they have once past, they are all of them equal, and whirl'd about with the same degree of swiftness. Forasmuch therefore as Comets are carried in the utmost parts of the Vortex, and borrow all the Light they reflect to us from the Sun, it follows, that those Beams of Light, which are communicated by the greater of those Globuli, by that time they come to the lesser, do not only pass according to Right Lines, by which, as being the chiefest, the Head of the Comet is seen by us, but are also refracted and dispersed side-ways. As if a Vessel should be so fill'd with Bullets, as that the great ones did lye upon the lesser, we shall find, that upon boring a Hole at the bottom of the Vessel, the greater Bullets lying at the top, must in their descent press upon more of the lesser, and drive them down to Right Lines. And the same thing is observed in Comets: For seeing that the Sun is much about in the midst between the Comet and the Earth, his Rays beating against the Comet, and scatter'd on every side of it, do produce the Hair of it: But when the Earth withdraws from the Right Line, which joyns the Centers of the Sun and a Comet, then the Beams of the Sun which are reflected towards us, do represent the Body or Head of the Comet; and those which are diffused towards the Edges of it, do represent its Beard or Tail. Which are called by either of their Names, as they either go before, or follow the Body of it.

XI. How Co∣mets come to appear with Tails, Hair, or Beams like Roses. The Figure will fully clear this Point. Let the Sun be S, the Circle through which the Earth runs in a Years time, 2, 3, 4, 5, according to the order of the said Ciphers. The term or limit from whence the Globuli begin to grow less and less, DEFG, and the Comet in our Heaven C. It is apparent that the Rays of the Sun darted against this Comet, towards all the parts of the Circle DEFGH, are in such a manner re∣flected thence, that those that fall perpendicularly upon F, do most of them tend towards 3; but some of them are scatter'd this way and that way; * 1.2and those which fall obliquely upon G, do not only tend directly towards 4; but are in part refracted towards 3: And lastly, that those which fall upon H, do not reach directly to the Circle of the Earth 2 3 4 5, but being reflected, tend towards 4 and 5. Whence it is evident, that when the Earth is in the part 3 of her Orb, the Comet C will appear to those that view it from thence, with Hair scatter'd on all sides of it, which sort of Comets are commonly called Roses: For the Rays that come directly from the Comet C, to 3, do represent the Head of it; and the weaker, which proced from E and G, towards 3, do afford the appearance of its Hair. But if the Earth be at 4, then the same Comet will be perceived by the strait Rays CG 4, and its Tail will appear directed only to one part, by the Rays that are reflected from H, and other places between G and H, towards 4. And in like manner, when the Earth is at 2, the Comet will be perceived by means of the direct Rays CE 2, and the Hair of it by the oblique Rays, which are plac'd be∣tween CE 2, and CD 2. Neither will there be any difference, save that when the Spectator is placed at 2, the Comet will appear in the Morning,

with its Hair going before it, but to the Spectator placed at 4, the Comet will appear in the Evening, with a Tail trailing after it.

XII. Why none of these ap∣pearances are ever perceived in the Pla∣nets. The Reason why the Planets never appear with Tails, Beards, or Hair scattered round them like Comets, is because the particles of the 2d Element, which encompasseth them, are not big enough to make Beams that enlarge and divide themselves in∣to many others; whereas those that are about the Comets, are always big enough for that purpose.

XIII. Whether Comets pre∣sage future events. Comets are commonly look'd upon as the fore∣runners of great Calamities, and are supposed to presage Storms and Tempestuous Weather, Deva∣stations, Famine, Wars, Death of Princes, Plague. Thus the Comet that appeared in VESPASI∣ANS time, is said to have presaged his Death; others the taking of Rome by ALARICUS; the Murther of the Emperour MAURICE, and destruction of MAHOMET; the Death of CHARLEMAIN; the irruption of the TARTARS into Silesia, and the cutting off of the Inhabitants Ears.

Such Stories as these are common amongst the vulgar, and believed also by many who think themselves much wiser than their Neighbours. But if we examine the matter, we shall find that the appearance of these Stars had no connexion at all with the things that hapned soon after their ap∣pearance. For if Comets be the signs of Wars, the death of Princes, &c. Why do these ever hap∣pen without the foregoing presages? Why do Kings die, Famin and Plague prevail, when no Comets at all have discovered themselves to give warning of these accidents to the World? True it is, that these events are sometimes ushered in by Comets, but more frequently happen without them.

Moreover, seeing that Comets pass about the Earth, how is it that they foretell Overthrow and Destruction to some, Success and Victory to others? Probably indeed we might be induced to own this power in Comets, if Kings only died when they appeared; if they could distinguish between persons, or if they only aspect Great-Men. But since we always find the Funerals of Princes and Great-Men, accompanied with so ma∣ny thousand of vulgar Exequies, have we not great reason to conclude, that they have no greater force or influence upon the former, than upon these latter?

XIV. The Affairs of Men are covered with great darkness. But some Body will say; it is certain that these kind of Stars are sometimes sent by God to de∣nounce some calamity or other to the World. Be it so, for I will not deny it; but by what Argu∣ment can it be proved, that the appearance of a Comet is to denounce this or the other particular event, rather than another? Has GOD ever by Revelation made known to us, that when a Comet moves towards the West, it denotes danger from things Foreign and without; and when to the East, danger from within? It is sure enough, that the Comets have no Power over us, and that it is only our Folly or Ignorance that makes us affraid of them.

Notes

• * 1.1

  Figure 17.
• * 1.2

  Figure 27. in the In∣stitutions.