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the Earth has actually suffered from one or many Shocks or near Pastages of Comets, before the Creation of Man ?
23. IV. Whether, setting aside any mystical and if you will cruer Senie, Mojes his own Account of the fourth Day, taken in the popular Senie, would not imply that the fixed Stars, beginning then to become visib c to the Earth, had been really created, not only during fome Part of the Night of the Fourth natural Day, but even much longer before! Since thc Rays of Light require much more than one Night's Time, to come from the fixed Stars to the Earth ; and especially in the Newtonian System ? For otherwise the Rays of Light, by which the fixed Stars, chiefly the farther most Ones, became then visible, muft have been coming to the Earth, long before the fixed Stars themselves were created.
29. The Sun's Parallax being known, we may know nearly the real Bigness of all the Comets whole Orbits have been or will be constructed : And we may know it exactly, when their periodical Times are known. For we want only that the apparent Diameter of each Comet be but once [or several times ] carefully oblerved ; especially in or near the Comets Perigee. Wherein Astronomers seem to have been too negligent.
30. However, because an Example will give more Light to this Discourse, I shall shew how I calculate the Bigness of The Comet of 1680, from what I remember I did myself observe. Whereby it will appear, That the Diameter of chat Comet was but equal to 0.06 Parts of the Diameter of the Earth.
31. Supposing, as one may do according to my Theroy, that the Suns Para lax might be of 1384 Seconds: And that the Semidiameter of the Earth was to the real Semidiameter of the Comet of 1680 as 100 to 6: Then laying As 100 is to 6, so are 138 4Seconds to 8“,3253 this la't Number will be the Semidiameter of the Comet seen from a Dilance equal to the Distance betwixt the Centers of the Earth and of the Sun. And again, supposing that the Comet, when I observed it near is second Perigee, did, by a Telescope, appear no bigger than Jupiter commonly does ; which was really the Case : At which i ime I reckon that the Distance of the Comet from the Center of the Earth, was to the Diftance betwixt the Centers of the Sun and of the Earth, as 53 to 100 nearly: Then saying 53 is to 100, as 8":325 60 15.1 Seconds This laft Number, as seen from the Earth, comes forth for the apparent Semidiameier of the Comet, when I saw that Comet as big as jupiter commonly does appear. Now that very Number of Seconds 15,1 being often the mean apparent Semidiameter of Jupiter very nearly ; it follows that the real Semidiameter of the Comet was but réo Parts of the real Semidiameter of the Earth very nearly; as I had supposed it, after I had first seen the Result of only two falie Suppositions.
32. And from chence it is manifest how exactly the real Bigness of Comets may be found out from accurate and proper Data.
33. But according to Sir Isaac Newton, who makes the Distance of the Sun at least about 13 times greater than I do; I must conclude that the Diameter of the Comet of 1680 would have been to the Diame
ter of the Earth, nearly as 78 to 100. Tho'according to his Conjecture p. 517, this be probably one of the smallest, or even the very smallett Comet of all. And in general the Danger from the Passage, or from the Shock of Comets, becomes much greater according to him than to me. For the Diameters of Comets, as well as their Swiftness, come forth at least 13 times greater, and the Breaches, which they make in the Planes of the Orbits of the Planets, become at least 13 times longer and 13 times broader, to him, than to me; while the Bodies of the Earch and of the Moon remain the same ; their Diitance from one another changing likewise very litde.
34. Sir Is. Newton did admirably shew how to determine the Orbits of Comets about the Sun, and their Swiftness in those Orbits. But here you have the firit justifiable Eftimation of the Bigness of a Comet; and a general Method to know quanti fint, borc big they are, according to Seneca's Expression. I did hope that Dr Halley (who had collected all the necessary Memoirs and Helps for determining exactly or ne irly the Bigness of all the Comets, whose apparent Diameters have been observed and t:eir Orbits described) would let the World know how great their Gobes must be, fuppaling the Sun's Parallax of what deter
Quant ty he pleased. For that would be sufficient in order to know their Bignels according to Sir Isaac Newton's Theory; or else according t mine. In the mean while it appears by what precedes, That the Semi diameters of the Earth and of the Moon being supposed of 100 and of 29,57 ?ar s respectively, the Semidiameter of the Comet of 1680 comes forth but of 6 Parts. Tho'according to the Newtonian System we might infer that the Semidiameter of that Comet was of about 78 Parts.
35. 'It is probable that the Danger, which the Comets expose the Earth unto, is multiplied in Proportion to the Number of the Comets contained in the Solar System. And we may colerably conje&ture their Number as follows: Tho this, for ought I know, was never attempted before. What is certain is that the Comers, that come within reach of our Observations, do seem not to be much fewer than 70 or 100.
36. Their Number may be guess'd at, by the Frequency of their coming to their Perihelium ; and together by a reasonable Efimation of the mean Length of their Periodical Revolutions.
37. As to their Frequency ; it appears, by Experience, that about Twelve Orbits of Comets may be observed Astronomically in One hun. dred Years ; so that those Orbits may be described, in consequence of the Observations. But many Comets do pass, either wholly unperceived ; or at least not sufficiently observed by our Aftronomers. The Comets, that appeared in 1607 and 1661, perform their Revolutions in 75,- and in 129 Years: And they descend much lower than the Orb of Venus. Upon both which accounts, they ought to be the more easily perceived ; viz. as moving more slowly; and as receiving a greater Light from the Sun. But yet (in the Systems of the Comets) cheir Revolutions in 13804 and 1456 ; and in 1403 ; are not mentioned. Other Comets, perhaps smaller or darker, or more unconveniently
placed placed, and at least swifter, and more remote from the Sun, may stil more eafily pass unobserved. Upon the whole it maybe supposed thaj 26 or 30 Comcts may alway come in 100 Years to their Perihelion.
38. As to the mean Periodical Time of the Revolution of Comets in general; the shortest of all seems hicherto to be of 75 Years ; and the longeit, of 5754. The mean Number is 325 Years. And the mean proportional is 208. Bue it is not impossible that some Comets may spend above 600 Years in one Revolution.
39. In the following Table, to be continued as far as you please, you may chuse, at Discretion, in the Column A, the Number by which you think you may best express how many Gomets come to their Perihelion in 100 Years. And in the uppermost or lowermost Line, you may chuse another Number expressing the mean Number of Years that you will allow to Comets for their Revolution. And, in the Area of the Table, you will find over against those two Numbers, how many Comes there must be, in the Solar System, in consequence of your Suppositions. For instance, If 20 (or 30) Comets do come in 100 Years to their Perihelium ; And if their mean Revolution be performed in 350 Years; Then the Table gives 70 (or 10;) for the whole Number of Comets.
A 1.0 150 200 250 300 350 100 450 500 550 603
15, 20, 25, 30 35 40 45 50, 55, 00
22 271 33/ 38 44 49' 55) 609 66 121
18! 24 30 361 42 48 54, 60, 66_72 14141 21; 28 351 42 49' 56, 63! 701 77: 841 16 16 24 32 40 48, 56 64 72 80' 88, 96 18. 181 271 36' 45' 54' 63 72 81 90: 99 108 204 201.30, 40150
70 90100110,120 22 33 44 55 66 77 88 99 110 121 132 24' 24' 36 481.601 721 841 96 108 120 132144 26, 26, 39 52, 651 781 9111041171130,1431156 28 28 42 56 70 84 98 112126140 154 168 30' 301 45' 60: 75' 90'105'120135 1501165180
100 150 200 250 300 350 400 450 500 550 600
40. Mercury's periodical Revolution is about 122 times Morter than that of Saturn. But hitherto the shortest Period for Comets seems to be but about 8 cimes shorter, than their longest Period And if there be 70 Comets in all; the mean Difference between their Revolutions seems to be but of 7 Years or thereabouts. But if there be 105 Comets ; that mean Difference seems to be but of about 5 Years.
41. The Spheroids, who'e longest Axis is terminated by the Apsides, and in which the Planets and their Satellites move about their Primary Planets, do not intersect one anoiher. So these Globes are in no Danger of hitting one against another, tho they revolve nearly in the same Plane. But it is not so with the Comets. For instance the Comet of 1680 is supposed by Sir I Jaac Newton to ascend higher than the ge.
nerallity of Comele. And if they did revolve in the Plane of the Ecliptic, they would, most of them, in each Revolution, pass twice thro the Circumference of the Great Orb, and indanger greatly our lower Syftem of the Earth and of the Moon. The like may be said of 'Mars, and of the other Planets and the Planes in which they revelve. Most wisely therefore did kind Providence place the Centers of the Orbits of the Comets in great and different Latitudes ; and in d fferent Longitudes ; in reference to an Eye placed in the Center of the Sun. As, on the other hand, by making some of them Direct, and some of them Retrogade, She does moderate and counterballance their Adions upon the Planetary System, and upon onç another.
42. Of the said Comets, some may now and then be observed from the Earth in their Transit under the apparent Disk of the Sun. And these curious Observations, which can be made only when ihę Sun shines, might be left, with Promise of a proper Recompence, to the Care of that Multitude of Officers and Seamen unoccupied in the Royal Hospital at Greenwich; where a sufficient Number of proper Witnesses are always at hand; and from whence Notice might be immediately given to the Royal Observatory. Now if there be about 100 Comets; their mean Revolution being supposed of 300 Years, I reckon that by a Medium, a Comet may be seen in the Disk of the Sun, once in about 800 Days.
43. How precarious then, upon the whole, considering the intire Theory of Comets, is the State of Mankind! How dependent upon God's immediate Goodness, Foresight and Providence ! And how easily, how suddenly and naturally, may this Globe of our Earth, and some other Celestial Globes, with the Creatures that are in them, be made severe Examples of His Julice ; as well as the Globes of the Comets themselves ! For nothing seems to hinder the Comers from be
ng inhabited : Since in the Perihelies of those that come nearett to the sun, such a Cloud or Chaos of mixt or even watry and incombustible Vapours may be raised, as may obstruct wholly the sight of the Sun'; and prevent not only his vitrifying or melting, but even his heating im moderately the Surface of the Globe. Thus, near our Tropics, che Winter or cloudy Sealan is, when the Adion or Power of the Sun is strongest there.
44. In Process of Time, as the Orbits and Periods of Comets may be discovered and 'seçtled more and more ; the whole Number of observable Comets contained in the Solar System will or may in like manner be discovered more and more exaály: 7 ill, after about 1500 or 2000 Years, the whole Multitude of those Comets, that may be easily seen from the Euth, becomes compleatly or very nearly known. Which mournful Knowledge Astronomers have had sufficient Time to make themselves Mafters of, but seems to be reserved for Posterity.
Revised and amended : Worceftir, March 1, 1742.
Nic. Facio Duillier
POST-SCRIPT. I think it necessary to add to my Discourse about Comets, a certain Criterion, by which it may commonly be known, which comets are dark B dies like the Earth or the Moon, having no other Light but wha they reiect, after having received it from the Sun: Or else which comes may be fiery Globes, or at least Globes shining by their own proper isnate Light, tho' not altogether of a fiery Nature. For it is only by O. servations, that these different kinds can be distinguishid.
And indeed, upon second thoughts, I must conclude that the Comet which appeared in 1680, did shine by its own proper Light not borrow. ed from che Sun. For I have been myself a Witness, that it appeared like an entire Globe of Light, when otherwise it ought to have appeared with Phases like Venus or the Moon.
Likewise, on the 21/4 of March, when the Comet which has appeared this Year was seen very near the North Pole, it seemed Globular, to fome Persons who saw it from our Garden with a four Foot Telescope: And it darted its Tail, sparkling by fits like a fixed Star; as allo Mr Doubarty Junior did observe. From whence we may probably conclude That it was a Globe of Fire; or at least a Globe Shining by its own proper Light.
TOL. Philip Mordaunt, Cousin-Germain to the famous Earl of
Peterborough, (who uled to boast he was the Man who had seen the greatest Number of Courtiers and Kings) was a young Man of Quality of about 27, well made, whole Birth and Genius gave him room to expect the greatest Advantages. He had placed all his Happiness in a Mistress, by whom he was passionately beloved. Yet in these Circumstances, he took a sudden Diftalte to Life, writ several Letters to bid his Friends farewel, and compos'd some Verses, t expressing his Determination to die by his own Hands. Accordirgly he shot himself through the Head, for no other Reason, but that his Soul was tir'd of his Body; and he thought, when a Man was weary of his Lodging, it
+ I bave never been able to see a copy of these in English, the Meaning of tbe lat
“ Starza run thus “'Opium may be serviceable to the Wise on this Occasions ; "bue in my opinion, a Brace of Balls and Resolution will do much better.” I. one of bis Letters be bad this Expreffion. “ Life bus given me ebe Headach, and I “ want a gond Churcb-Yard Sleep, to jet me right, "