prefent Theory, that one would be apt to think he had presaged all that later Experience and Obfervations have discovered.",

We shall now Examine what M. Maupertuis himself fays of Comets from his own Knowledge in Aftronomy and Geometry,

In order to illuftrate this Subject, as Comets form a Part of our general Solar Syftem, the Author gives us a fhort View of it, in a clear and diftinct Light. We fhall only take that Part of it, which is ⚫ neceffary for understanding the Subject in Queftion.

We will suppose the general Syftem of the World, known to most of our Readers, even thofe of the fair Sex, many of whom have ac quired the Knowledge of the abftrusest Parts of natural Philosophy ⚫ and Phyfick.

The Planets then describe Ellipfes about the Sun, who does not fill ⚫ the Centre of their Orbits, but is placed in a Point we call the Focus, i. e, which is nearer the Extremity of one part of the Curve than the other, and is fo much nearer in Proportion to the Elongation of the Ellipfis. On this Account it is, that the Planets in certain Parts or Points of their Orbits, which we term their Peribelion, approach ⚫ nearer the Sun, than in other Points, which are called their Aphelion: But as the Ellipfes which our Planets, viz. Mercury, Venus, the Earth, Mars, Jupiter and Saturn, describe around the Sun, differ but a little from Circles, we never lofe fight of them in the Course of their periodical Revolutions.

Comets differ from Planets only in this, that in their Courses round the Sun, who is their common Focus, they form Ellipfes extremely oblong of various Degrees. Confequently they take up in their Revolutions a much longer Space of Time than the Planets, and this in • Proportion to the Length of their Ellipfes.

This Elongation of the Comets with regard to their Orbits, joined to the Slowness of their Revolutions, has prevented, hitherto, our com⚫ing to any Certainty as to the exact Time of their Returns. We never lofe fight of the Planets, because they never go beyond fuch a Diftance; whereas the Comets are only visible to us during that fort part of their Course which lies near the Earth, the rest being spent in the most diftant Regions of the Heavens, during which they are entirely loft to us. So that when a new Comet appears, we have no ⚫ other way to know it again, than by examining what Comets have appeared before at fuch certain Periods of Time, and comparing their • Courfe with that of the new Comet, if we can make any certain Ob⚫ fervations upon it.

It is by this Method, that we have probable ground to believe, that the Comet of 1682 finishes its periodical Revolution in 75 Years, for we find in 1607 there appear'd a Comet, which feem'd to have the fame Mction, another in 1531, and a fourth in 1456, fo that it is likely all thefe Comets were one and the fame. This will be yet more certain of it fhould re-appear in 1757 or 1758.

M. Maupertuis inftances the Example of two other Comets, whofe Revolutions have been calculated, but the Proofs do not feem fo ftrong. It is only from Obfervation and Time that we can hope to bring the Theory of Comets to Perfection, but as to the Courfe of any particular

Comet,

Comet, we may be more certain. Subject to the fame Laws that direct the other planetary Bodies, no fooner a Comet appears and has mark'd its Orbit in any known Point of the Heavens, but we may by Theory determine its Progrefs, and with regard to thofe Comets that have hitherto been carefully obferved, the Event has verify'd the Calculation.

Of this we have a remarkable Proof in the Comet of 1664. Mr Caffini after a few Obfervations exactly foretold the Rout it held, which we hall relate in the Words of our Author himself.

He (M, Caffini) was fo fure of his Syftem, in refpect to Comets, that after his first two Observations taken the 17th and 18th Nights in December, he boldly mark'd out, to the Queen, on the celestial Globe, theCourfe it would take; after a fourth Observation, made on the 22d, ⚫he afferted it was not yet in its nearest Proximity to the Earth, which on the 23d, he predicted would happen on the 29th, and tho' at that • Time it exceeded the Moon in Swiftnefs, and feem'd likely to make the Tour of the Heavens in a fhort Time, he afferted that it would ⚫ftop in Aries from which it was then but two Signs diftant, and after refting there, would move in a retrograde Direction to that which it had held. Many laugh'd at these Predictions, and were incredulous enough to maintain that the Comet would cheat the Philofopher, but when they faw it fulfil his Calculation, they were glad to recant their • Error,

We have already remark'd with our Author how much Comets are fallen into Difefteem with respect to their Influence, in return M. Maupertuis is willing to make them fome Recompence for this Lofs by giving them. Credit another way. According to him, as phyfical Causes, they are capable of producing the most important Events. The cele brated Mr Halley, who has calculated the Orbit's of 24 Comets from aftronomical Obfervations, has concluded from thence, that they move in all Directions, fome in the Order of the Signs, others in a retrograde Courfe, their Circles interfe&ting the Earth's Orbit in all Points, and having nothing in common, but being described around the Sun as their mutual Focus.

In fuch a Variety of Motions, it is eafy (fays our Author) to fee how poffible it is for a Comet to meet fome Planet, or even our Earth in its way, and produce the moft terrible Effects. The bare Approach of two fuch vaft Bodies would occafion violent Alterations in ⚫ their Motions, either by the Attraction they would exert towards each ⚫ other, or by the Compreffion of their Atmospheres. The leaft that ⚫ could happen in this Cafe, would be no less than to change the Situa

tion of the Axis and Poles of our Globe. That Part of the Earth, • that now lies under the Equator, would be turn'd to the Poles, and • vice verfâ.

Nor have we lefs to fear from the Tails of Comets than their Bodiesthemselves. These are probably only immenfe Torrents of fiery Exhalations or Vapours, which the folar Heat forces from their Bodies. Now a Comet may país fo near the Earth, as to overwhelm us in this igneous Train, which it draws after it, or in an Atmosphere of the fame Nature which surrounds it.

The

TheMotion of the Earth may otherwife, by thefe means, be fo chang'd, as to convert it into a Comet itself. Another Accident which if not fo fatal. would be at leaft as humbling to our terreftrial Planets, would be, if fome large Comet, by coming too near it should force it from its Orbit, and fubject it to make its Revolution round it. In this Cafe the Earth becoming the Satellite of this Comet, would be constrain'd to attend her to the Extremities of the Heavens. By the fame Means a Comet might rob us of the Moon, and happy if we escape fo cheap. The worst would be if a Comet by its fhock fhould crush us to Pieces.

Thus we fee that M. Triffotin had been lefs ridiculous if he had plac'd a Comet inftead of a World in thefe Lines Moliere makes him speak, Scene 3. A&t 4. of the [Femal Pedants] learned Women.

Je viens vous annoncer une grande nouvelle,
Nous l'avons, en dormant, Madame, echappé belle:
· Un Monde prs ède nous a paffe tout au long,
Eft chû tout à travers de notre Tourbillon,
Et s'il eût, en chemin, rencontré notre Terre,
Elle eût été brifée en morceaux comme verre.

If our Earth (proceeds M. Maupertuis) has as yet fuffer'd none of thefe dreadful Cataftrophies, it has at leaft felt fome Effects of the • Force of Comets. The Marks of petrify'd Fishes and Shells, found in Places vaftly diftant from the Sea, and even on the Tops of • Mountains, are inconteftable Marks of fome of thefe Events.

An ingenious English Author (Mr Whifton) advances, that the natural Caufe which God made ufe of to produce the Deluge was the fame Comet which appear'd in 1680, which approached so near the Sun that it received a Heat 28 Millions of Times greater than what the Earth had from the Sun. In tracing back from the Appearance of this Comet in 1680, he finds another appear'd in 1106, another in 531 or 2, and another at the Death of Julius Cæfar 44 Years before Chrift. All these Comets, which he concludes the fame, keep a Period of 575 Years, and the 7th Period upwards, from 1680, falls exactly in with the Year of the Deluge. Mr Whiston thinks that the mutual Attraction of the Earth and this Comet, changed the Figure of the former, and, by lengthening it towards the latter, broke the external Cruft or Surface of the Earth, and made way for the Waters contained in the great Abyss to overflow the Earth. The fame Author imagines that a Comet, perhaps the fame in its Return from the Sun, will occafion the Conflagration that is to confume the Earth at the Day of Judgment.

Some may call these Ideas of Mr Whifton Vigilantis Somnia, or learned Reveries. The Reader may fee what M. Mairon has faid on this Subje& in his Treatife on the Aurora Borealis.

According to M. Maupertuis, these physical Powers of the Planets demand fome Refpect to be paid them, yet we don't find they are very formidable at prefent, except to fuch Philofophers as Mr Whifton. Were they really fo, it is impoffible to perfwade the Bulk of Mankind, that Bodies fo minute to the naked Eye, can ever produce fuch great EMen cafily fwallow Things contrary to Reason, but it is hard

vents.

to

to perfuade them their Senfes deceive them. M. Maupertuis however thinks proper to difpell our Fears on this Occafion by these Reflexions.

The Duration of Life, fays he, is fo fhort, and the Knowledge we have from Experience, that no fuch Accident has happened for fo many thousand Years, are fufficient to prevent our Dread of being either the Witneffes or Victims of fuch a Calamity. Terrible as Thunder is, its Fall is lefs to be apprehended by each Individual from the fmall Space he occupies in the Extent where it defcends. In like manner the fhort Portion of Time we enjoy in that Eternity in which these great Events happen, annihilates to us the Danger, tho' it does not alter the Nature of Things.

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M. Maupertuis is not fatisfy'd only with comforting his fair Correfpondent, and difpelling her Apprehenfions. He finishes his Letter yet more agreeably by giving her Hopes; he tells her that a Comet by a flight Shock fo alter the Axis of our Globe, as to procure us a conftant Spring, or, by gently changing its Orbit, make it describe an exact Circle round the great Source of Light and Heat. We have obferved a large Comet may deprive us of the Moon, but if it be small, it may in its turn ferve us as a fecond Moon. Perhaps the one we enjoy at prefent was originally a Comet, who by approaching too near us, was prefs'd into our Service.

To conclude, even the Tail of Comets is a Plunder may enrich us. We may happen, without any ill Confequences, to appropriate one of thefe as a Ring, like that of Saturn, which (according to our Author in his Treatife upon the Planets) is only the Remnant of a broken Comet's Tail.

In this Letter M. Maupertuis has abridg'd the Theory of Comets in a Manner fo agreeable, clear and eafy, that the Piece appears to be the Work of a Philofopher, who is equally known for his Genius and Politeness, as for his profound Knowledge as an Aftronomer and Mathematician.

FINI S.

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