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DUKE 
 
 UNIVERSITY 
 
 LIBRARY 
 
 Treasure %oom 
 
A N 
 
 E S S AY 
 
 Towards a History of 
 
 COMETS. 
 
A N 
 
 ESSAY 
 
 Towards a History of the 
 PRINCIPAL COMETS 
 
 That Have 
 
 Appeared fince the Year 1 742. 
 
 Including a particular Detail of the Return of the famous Co- 
 met of i<58z in 1759, accordin^to the Calculation and Pre- 
 ' diction of Dr. Halley. Compiled from the Obfervatlons 
 of themoft eminent Aftronomers of this Century. 
 
 "With Remarks and Reflections upon the 
 PRESENT COMET. 
 
 To which is prefixed, 
 
 A Letter upon Comets, 
 
 Addressed 
 
 To the Marchioness du Chatelet, 
 
 By the late 
 M. D E M A U P E R T U I S. 
 
 With a fhort Account of the Life of that celebrated 
 Astronomer and Mathematician. 
 
 GLASGOW: 
 Printed for R o b e r t U r i e. 
 
 MDCCUX. 
 

w mio£z$> 
 
 A 
 
 Summary Account 
 
 OF THE LIFE OF 
 
 M. DE MAUPERTUIS. 
 
 PETER Louis Morceau de Maupertuis was 
 born at St. Malo, the 28th of September, 
 1 698, and was there privately educated till he ar- 
 rived at his fixteenth year, when he was placed 
 under the celebrated profefTor of philofophy M. le 
 Blond, in the college of la Marche, at Paris. He 
 foon difcovered a paffion for mathematical ftudies, 
 and particularly for geometry. ' He likewife prac- 
 tifed inftrumental mufic in his early years with 
 great fuccefs ; but fixed on no profellion till he 
 was twenty, when he entered into the army. He 
 firft ferved in the grey mufqueteers; but in the 
 year 1720, his father purchafed him a company 
 of cavalry in the regiment of La Rocheguyon. 
 
 He remained but five years in the army, dur- 
 ing which time he purfued his mathematical ftu- 
 dies with great vigour ; and it was foon remarked 
 by M. Freret, and other academicians, that n> 
 A 
 
2 T H E L I F E 
 
 thing but geometry could fatisfy his active foul, 
 and unbounded thirft for knowlege. In the year 
 1723 he was received into the royal academy of 
 fciences, and read his firft performance, which 
 was a memoir upon the conflrue~Hon and form of 
 mufical inftruments, Kovemberi5, 1724. 
 
 During the firft years of his admifTion he did 
 riot wholly confine his attention to mathematics ; 
 he dipt into natural philofophy, and difcovered 
 great knowlege and dexterity in obfervations and 
 experiments upon animals. 
 
 If the cuftom of travelling into remote climates, 
 like thefages of antiquity, in order to be initiated 
 into the learned myfteries of thofe times, had (til! 
 fubfifted, no one would have conformed to it 
 with greater eagernefs than M. de Maupertius. 
 His firft gratification of this paflion was to vifit 
 the country which had given birth to Newton ; 
 and during his refidence at London he became as 
 zealous an admirer and follower of that philofo- 
 pher as any one of his own countrymen. 
 
 His next excurfion was toBafil in Switzerland, 
 where he formed a friendfhip with the fsmous John 
 Bernouilli and his family, which continued to his 
 death. 
 
 At his return to Paris, he applied himfelf to 
 his favourite ftudies with greater zeal than ever, — 
 and how well he fulfilled the duties of an acade- 
 
OF MAUPERTUIS. 3 
 
 mician, may be gathered by running over the me- 
 moirsofthe academy, from the year 1724, to 
 1 736 ; where it appears that he was neither idle, 
 nor occupied by objects of fmail importance. The 
 moil fublime queftions in geometry, and the re- 
 lative fciences, received from his hands that ele- 
 gance, clearnefs and precifion, fo remarkable in 
 all his writings. 
 
 In the year 1736 he was fent by the king of 
 France to the polar circle, to meafure a degree in 
 order to afcertain the figure of the earth, accom- 
 panied by MefTrs. Glairaut, Camus, le Monnier, 
 1'Abbe Outhier, and Celfius, the celebrated pro- 
 fefTor of aftronomy at UpfaJ. This diftincYicn 
 rendered him fo famous, that, at his return, he 
 was admitted a member of almoft every academy 
 in Europe. 
 
 In the year 1 740, he had an invitation from the 
 king of Pruflia to go to Berlin, which was too flat- 
 tering to be refufed. His rank among men of 
 letters had not wholly effaced his love for his firir. 
 profeflion, namely, that of arms. He followed 
 his Pruflian majefty into the field; and was a wit- 
 nefs of the difpofitions and operations that pre- 
 ceded the battle of Molwitz ; but was deprived 
 of the glory of being prefent, when victory de- 
 clared in favour of his royal patron, by a lingular 
 kind of adventure. His horfe, during the heat of 
 A 2 
 
4 T H E L I F E 
 
 the a&ion, running away with him, he fell into 
 the hands of the enemy, and was at flrft but 
 roughly treated by the Auftrian foldiers, to whom 
 he could not make himfelf known, for want of 
 language ; but being carried prifoner to Vienna, 
 he received fuch honours from their imperial ma- 
 jeures as were never effaced from his memory. 
 
 From Vienna he returned to Berlin ; but as 
 the reform of the academy which the king of 
 PruiTia then meditated, was not yet mature, he 
 went again to Paris, where bis affairs called him, 
 and was chofen, in i 742, director of the acade- 
 my of fciences, 
 
 The comet which appeared this year gave rife 
 to the following letter : it was ad-dreffed to the 
 celebrated marchionefs du Chatelet, whofe love for 
 the fciences extended even to the ftudy of mathe- 
 matics : and fhe had M. de Maupertuis for her 
 matter in geometry, and the Newtonian philofo- 
 phy. 
 
 In 1743 he was received into the French aca- 
 demy. This was the firft inftance of the fame per- 
 fon being a member of both the academies at Paris, 
 at the fame time. 
 
 M. de Maupertius again affumed the foldier at 
 the liege of Fribourg, and was pitched upon, by 
 marfhal Cogny and the count d'Argenfon, to car* 
 
OF MAUPERTUIS. 5 
 
 ry the news to the French king of the furrender 
 of that citadel. 
 
 He returned to Berlin in the year 1 744, when 
 a marriage was negotiated and brought about by 
 the good offices of the queen mother, between 
 our author and mademoifelle de Borck, a lady of 
 great beauty and merit, and nearly related to M. 
 de Borck, at that time minifter of ftate. This 
 determined M. de Maupertuis to fettle at Berlin, 
 as he was extremely attached to his new fpoufe, 
 and regarded this alliance as the moft fortunate 
 circumftance of his life. 
 
 In the year 1746, he was declared by his Pruf- 
 iian majefty, prelident of the royal academy of 
 fciences at Berlin, and foon after by the fame 
 prince was honoured with the order of Merit. 
 
 However, all thefe accumulated honours and 
 advantages, fo far from lefTening his ardour for 
 the fciences, feemed to furnifh new allurements 
 to labour and application. Not a day paffed but 
 he produced fome new project or elTay for the ad- 
 vancement of knowlege. Nor did he confine him- 
 felf to mathematical ftudies only: metaphyfics, 
 chymiftry, botany, polite literature, all fliared 
 his attention, and contributed to his fame. 
 
 But bis conftitution, though naturally robufr, 
 focn felt the effects of this intemperance, in his 
 philofophical purfuits. Indeed his health had been 
 A 3 • 
 
6 THE LIFE 
 
 confiderably impaired before, by the great fatigues 
 of various kinds in which his active mind had in- 
 volved him. Though from the amazing hard- 
 fhips he had undergone in his northern expediti- 
 on, moft of his future bodily fufferings may be 
 traced. The intenfe fharpnefs of the air could 
 only be fupported by means of ftrong liquors, 
 which helped but to lacerate his lungs and bring 
 on a fpitting of blood, which began at leaft twelve 
 years before he died. 
 
 Yet ftill after his bodily ftrength was thus im- 
 paired, his mind feemed to enjoy the greateft vi- 
 gour, for the beft of his writings were produced, 
 and moft fublime ideas developed, during the 
 time of his confinement by ficknefs, when he was 
 unable to occupy his prefideal chair at the aca- 
 demy. 
 
 M. de Maupertuis took feveral journeys to St. 
 Malo, during the laft years of his life, for the re- 
 covery of his health. And though he always re- 
 ceived benefit by breathing his native air, yet 
 ftill, upon his return to Berlin, his diforder like- 
 wife returned with greater violence. — His laft: jour, 
 ney into France was undertaken in the year I 7^7, 
 when he was obliged, foon after his arrival there, 
 to quit his favourite retreat at St. Malo, on ac- 
 count of the danger and confufion which that town 
 
OF MAUPERTUIS. 7 
 
 was thrown into, by the arrival of the Englifti in 
 its neighbourhood. 
 
 From thence he went to Bourdeaux, hoping 
 there to meet with a neutral fhip to carry him to 
 Hamburgh, in his way back to Berlin ; but, being 
 difappointed in that hope, he went to Touloufe, 
 where he remained feven months. He had then 
 thoughts of going to Italy, in hopes a milder 
 climate would reftore him to health ; — but find- 
 ing himftlf grow worfe, he rather inclined towards 
 Germany, and went to Neufchatel, where for 
 three months he enjoyed the converfntion of lord 
 Marfhal, with whom he had formerly been much 
 connected. At length he arrived at Bafil, Octo- 
 ber 16, 1758, where he wascreceived by his 
 friend Bernoulli, and his family, with the utmoft 
 tendernefs and afTecYion. He at firft found him- 
 felf much better here, than he had been at Ncuf- 
 chatel ; but this amendment was of fhort duration, 
 for as the winter approached, his diforder return- 
 ed, accompanied by new and more alarming fymp- 
 toms. 
 
 He languished here many months, during which 
 he was attended by M. de la Condamine, the old- 
 eft and deareft of his friends. But his fear of a- 
 larming madame de Maupertuis, and expofing her 
 to the hazards and fatigues of a long journey, made 
 him conceal his danger from her, though he ar- 
 
8 T H E L I F E, etc. 
 
 dently wimed to fee her. However, the truth of 
 his fituation, at length, reached her at Berlin, and 
 fhe fet out with the utmoft precipitation, (for this 
 lady was a pattern of conjugal affection, as well 
 as of all other virtues,) but fhe was flopped on 
 the road, by an exprefs from MeflT. Bernouilli and 
 de la Condamine, with the melancholy news, that 
 on July 27, 1 759, death had put an end to his 
 fufFerings. 
 
 , 
 
LETTER upon COMETS, 
 
 ADDRESSED 
 To the Marchioness du Chatelet. 
 Tu ne qucefieris fit re nefas* 
 
 YO U defire my opinion, madam, concern- 
 ing the comet which is at prefent the general 
 topic of converfation throughout Paris ; and your 
 wifhes are to me commands. But what can I fay 
 to you of this ftar ? Shall I enquire into the in- 
 fluence it may have, or the events it may portend ? 
 A different ftar has decided the events of my life; 
 and upon that my fate folely depends. To co- 
 mets, therefore, T abandon the fate of kings and 
 empires. 
 
 It is not a century flnce aftrology was in vogue 
 both in court and city; aftroncmers, philofophers, 
 and divines, agreed in thinking comets the caufes 
 or forerunners of great events. Some few, in- 
 deed, rejected this fpecies of divination by aftrolo- 
 gical rules: a modern author, celebrated for his 
 
io T H E H I ST O R Y 
 
 piety and agronomical learning, believed this kind 
 of curiofity more capable of offending an already 
 incenfed God, than of appealing his indignation; 
 and yet he could not refrain from giving us a lift 
 of all the great events which comets have already 
 preceded, or followed *. 
 
 Thefe Oars, after having been fo long the ter- 
 ror of the world, are fuddenly fallen into fuch dif- 
 repute, that they are no longer held capable of 
 producing any thing but colds. It is not the pre- 
 fent humour to believe, that bodies fo remote as 
 comets can have any influence upon fublunary 
 things ; or can be meant as flgns of what will hap- 
 pen in future. For what relation can there be be- 
 tween thefe ftars, and what pafles in the councils 
 or armies of kings ? 
 
 I mall not examine the metaphyfical poffibility 
 of thefe things, either as to the influence, which 
 neighbouring bodies reciprocally have upon each 
 other, or that which the body has on the mind, 
 of which, however, we cannot doubt, fince on that 
 frequently depends the happinefs or mifery of our 
 lives. 
 
 But as to the influence of comets, our know- 
 lege muft arife either from revelation, reafon, or 
 experience : and we may venture to fay, that we 
 
 * Riccioli Almageft. lib. viii. cap. j and 5. 
 
OFGOMETS. ii 
 
 have not yet found it in any one of thefe fources 
 of our intelligence. 
 
 The exiftence of an univerfal connection be- 
 tween every part of nature is very certain, as well 
 in the phyfical, as in the moral world : each event 
 being connected with that which precedes, and to 
 that which follows it, as a link of that chain which 
 forms the order and fuccefTion of things : if it was 
 not placed as it is, the chain would be different, 
 and appertain to another univerfe. 
 
 Comets then undoubtedly conftitute a part of 
 the great chain of nature ; but the finging of birds, 
 the fwarming of bees, the minuted atom that 
 floats in air, form likewife a part of this wonder- 
 ful concatenation : and it would be equally reafon- 
 able to confult them, as comets. In vain have we 
 an idea of this fcale of beings ; we draw no ad- 
 vantage from it to enable us to forefee events, when 
 their dependencies are fo remote : our fafeft rule 
 is, therefore, to be content with difcovering events, 
 from thofe things only whofe connection is more 
 immediate and manifeft. 
 
 "We may compare ailrologers to adepts, who 
 are for ever labouring to draw gold from materials 
 which only contain its principles and mod trivial 
 feeds ; they lofe their time and labour, whilft the 
 rational chymift enriches himfelf by extracting gold 
 
12 THE HISTORY 
 
 from earths and minerals, where it is already 
 formed. 
 
 To endeavour at difcovering the connections 
 thatfubfift in nature, is no way inconfiftent with 
 prudence ; but it is downright folly to pufh thefe 
 refearches too far ; as it is the lot only of fuperi- 
 or beings to fee the dependance of events, from 
 one end to the other, of the chain which fup- 
 ports them. I mall therefore not entertain you 
 with that kind of influence of comets; nor fpeak 
 but of things within our conceptions, and for 
 which we can give mathematical demonllration, or 
 phyfical reafons. Neither (hall I enter into a de- 
 tail of all the ftrange ideas, which fome have en- 
 tertained concerning the origin, and nature of 
 comets. 
 
 Kepler, to whom, in other particulars, aAro. 
 nomy has fuch great obligations, thought it but 
 reafonable, that as the fea has its whales and mon- 
 gers, the air mould have them likewife. Thefe 
 monfters ate comets: and he explained, how the 
 excrement of the air engendered them by an ani- 
 mal faculty. 
 
 Some have believed that comets were created ex- 
 prefsly when they were neceflary to announce to 
 man the defigns of God; and that angels were 
 their conductors. They added, that this expli- 
 
OF COMETS, 13 
 
 cation folved all the difficulties that could be raifed 
 on this point*. 
 
 In fhort, that all poflible abfurduies on this 
 fubjeft might be exhaufted, there have been thofe 
 who have denied the exigence of comets ; and 
 who have taken them for falfe appearances, occa- 
 fioned by the reflection, or refraction of light. But 
 they alone can comprehend how this reflection, or 
 refraction could be made, without the exiftence 
 of a body to occafion itf. 
 
 To Ariftotle, comets were meteors formed of 
 fublunary exhalations ; and this, we may eafily fup- 
 pofe, was the opinion of a herd of philofophers, 
 who neither believed nor thought but in confor- 
 mity to his doctrine. 
 
 Anterior to this, the ideas of comets were more 
 juft. The Chaldeans, it is faid, knew they were 
 durable ftars, and a kind of planets ; and had even 
 calculated their revolutions. Seneca embraced 
 this opinion, and fpeaksof comets in a manner Co 
 conformable to our prefent notion of them, that 
 one might fay, be predicted what experiment and 
 modern obfervation have fince ratified ; for, after 
 allowing them to be real planets, he adds, ' Ought 
 ■ we then to be furprifed, if comets, whofe ap- 
 6 pearances are fo rare, feem not yet fubjecled to 
 
 *MasHinus, Tannerus, Arriaga, dec. f Tanxtius. 
 
 B 
 
14 THE HISTORY 
 
 « fixed laws ; or that we are yet unable to deter- 
 
 * mine the courfe of ftars, whofe returns are not 
 
 * made till after fuch great intervals of time ? It 
 ' is not quite fifteen hundred years flnce the Greeks' 
 
 * afcertained the number of ftars and named them : 
 
 * many nations, at prefent, only know the heavens 
 
 * from what their eyes behold, and cannot account 
 < for the difappearance of the moon at certain pe- 
 1 riods, nor what is the fhadow that conceals her 
 1 from us. It is but lately that we ourfelves have 
 1 had certain knowlege of thefe things; but the 
 
 * day will come, however, when time, and the 
 ' diligence of pofterity, (hall difclofe that of which 
 
 * we are now ignorant. One age is not fuffieient 
 6 to make fuch great difcoveries, though our time 
 8 were entirely devoted to them : what then have 
 ' we to hope, who make fuch a miferable divifloa 
 
 * of it, between ftudy and vice*?' 
 
 I (hall now, madam, proceed to explain to you 
 what aftronomy and geometry have taught us of 
 comets: and that which cannot be mathematically 
 demonftrated, I will endeavour to fupply by fuch 
 conjectures as to me appear moft probable, You 
 will think, perhaps, after having for a long time 
 paid too great refpeft to comets, that we begin all 
 at once to regard them with too much indifference. 
 
 • Seneca, Natur. Queit. lib. -7. 
 
Of COMETS, *5 
 
 To convey to you an idea of the importance of 
 thefe ftars, we mull begin by faying, that they are 
 not inferior in nature to planets, nor even to our 
 earth. Their origin appears as ancient, their mag- 
 nitude furpafTes that of many planets, and the 
 matter of which they are formed is of equal foli- 
 dity; and they even may, like the earth, have 
 their inhab'tants. In mort, if the regular planets 
 appear in fome refpecls to have advantages over 
 xomets, thefe have reciprocally advantages over 
 planets. Now as comets compofe a part of the 
 fyftem of the world, I cannot make you perfectly 
 underftand them, without previoufly giving you a 
 fketch of that fyftem. But in order to facilitate 
 your intelligence of it, I wifh you had now before 
 you Dr. Halley's chart of the folar fyftem, with 
 the explanation, in which the orbits, or paths of 
 comets, are marked. 
 
 ■-.- The fun is an immenfe globe of celeftial fire, 
 or of matter more like fire than any thing we know 
 of; but notwithftanding ks prodigious fize, it oc- 
 cupies a point only of that infinite fpace in which 
 it is placed. We muft not therefore call the point 
 it occupies, either the centre, or extremity of this 
 fpace, as that would imply a figure and bounda- 
 ries. Each fixed ftar is- alfo a fun which belongs 
 to another fyftem. 
 
 While qur fun revolves on its own axis in the 
 B 2 
 
16 THE HISTORY 
 
 fpace of twenty-five days and a half, the matter 
 of which it is compofed flies off in al! directions, 
 extending its rays to a prodigious diftance ; not 
 only as far as our globe, but an immenfe way 
 farther. This matter, of which light is formed, 
 moves with fuch aftoniming rapidity, that it em- 
 ploys but half a quarter of an hour in travelling 
 from the fun to the earth. It is reflected back 
 when it falls on bodies it cannot pierce ; and it is 
 by this light we perceive the opake bodies of the 
 planets, which reflect it back again to us ; for 
 when the fun is hidden from us under the other 
 hemifphere, it permits this feeble luftre to become 
 perceptible. 
 
 There are fix planets which have no light but 
 that which they receive from the fun : thefe are 
 Mercury, Venus, the Earth, (which cannot be de- 
 nied a place among them) Mars, Jupiter, and Sa- 
 turn. Each of them defcribes a great orbit round 
 the fun, and as they are all placed at different di- ' 
 fiances perform their revolutions round him in dif- 
 ferent times. Mercury, which is the neareft, finifhes 
 his courfe in three months : next to the orb of 
 Mercury is that of Venus, whofe revolution is com- 
 pleted in eight months; then the orbit of the 
 Earth, placed between thofe of Venus and Mars, 
 is run through in one year, by the planet which we 
 inhabit j Mars employs two years to finifh his 
 
OF COMETS. 17 
 
 courfe ; Jupiter twelve, and Saturn thirty. One 
 remarkable circumftance in the revolutions which 
 thefe ftars make round the fun, is, that they are 
 all performed the fame way; that is, apparently, 
 from eaft to weft; which made a famous feci: of 
 philofophers * think, that the planets fwam in a 
 great vortex of fluid matter, which, turning round 
 the fun, carried them along with it, and was the 
 caufe of their motion. 
 
 But befides that the laws which govern the mo- 
 tion of planets, if well examined, is repugnant to 
 fuch a vortex, you will prefently perceive that the 
 motion of comets proves the utter impotfibility of 
 it. Many planets in performing their revolutions 
 round the fun, turn at the fame time on their own 
 axis: perhaps they all have fuch a rotation ; but 
 we are not allured of any, except the earth, which 
 does it in 24 hours; Mars in 25 ; Jupiter in 10 ; 
 and Venus. But though all aftronomers agree in 
 allowing to this planet a revolution upon its own 
 axis, of which they are aftured by the diverfity of 
 faces (he prefents to us, they are not, however, 
 yet agreed upon the time of this revolution : fome 
 fay fhe performs it in 23 hours, and others in 24 
 days. 
 I have not mentioned the moon here, as (he is not 
 
 * The Cartefians. 
 
 B 3 
 
i8 THE HISTORY 
 
 a planet of the firft order; nor does fhe perform 
 her revolution immediately round the fun, but 
 round the earth, which at the fame time carries her 
 with her in the orbit (he defcribes. Such planets 
 as thefe are fecondary y or fatellites : and as the 
 earth has one, fo Jupiter has four, and Saturn 
 five. 
 
 It is but lately that the laws, by which the planets 
 moved round the fun, have been difcovered ; and 
 thefe laws of their motion, which were difcovered 
 by the happy Kepler, have alTifted the great New- 
 ton to invedigate their caufes. 
 
 He has demonftrated, that as the planets move 
 in the manner they do, round the fun, it is necef- 
 fary that there mould be a force which draws them 
 continually towards this (tar; without which, in- 
 ltead of defcribing curve lines, as they do, each of 
 them would defcribe right lines, and become more 
 and more diftant from the fun, to infinity. He 
 has difcovered the proportion of that centripetal 
 power which retains the planets in their orbits, and 
 by this means has found the nature of thofe curves 
 which this power will neceflarily make them de- 
 fcribe. 
 
 All thefe curves are reducible to conic fecti. 
 ons ; and obfervation mews us that all planets de- 
 fcribe el'ipfes round the fun, which are oval curves 
 
OF COMETS, 19 
 
 formed by cutting a cone in a plane oblique to its 
 axis. 
 
 It is demonftrated by geometry, that the fun 
 cannot be in the centre of thefe ellipfes ; but to- 
 wards one of their extremities, in a point which 
 is called the focus : and this focus is fo much near- 
 er the extremity of the ellipfes as it is the more 
 excentric. The Sun's place is in this point : and 
 from thence it happens, that, in certain times of 
 their revolution, and in particular parts of their 
 orbits, which are called their perihelions ', the pla- 
 nets are found neareft the Sun ; and that in others 
 (when they are in their aphelion*} they are molt 
 diflant from it. Of the fix planets we have men- 
 tioned, thefe different diftances are not very con- 
 fiderable, becaufe the ellipfes they defcribe are not 
 very excentric, deviating but little from circular 
 figures. But the fame law by which we obferve 
 them to form thefe ellipfes, permitting them to 
 defcribe ellipfes of every degree of excentricity ; the 
 bounds, which nature feems to have prefcribed to 
 thefe orbits of the planets would be matter of afto- 
 nifhment, did we not find a greater diverfity in thofe 
 defcribed by the new liars. Comets now fulfil 
 what calculation forefaw, and what feemed defici- 
 ent in nature. Thefe new planets are always 
 fubject to the fame law as the other fix ; but mak- 
 ing ufe of the utmoil liberty which this law per* 
 
to THE HISTORY 
 
 mits, defcribe round the Sun ellipfes very excen- 
 tric, and of all degrees of elongation. 
 
 The Sun, placed in the focus common to e- 
 very ellipfes nearly ciicular, which the fix planets 
 defcribe, is likewife found in the focus of all the 
 other ellipfes which comets defcribe. The revo- 
 lutions of thefe laft round him are regulated by the 
 fame laws as the revolutions of the others : Their 
 orbits once determined by obfervations, we can 
 calculate their different places in the heavens for 
 the reft of their courfe ; and thefe places anfwer to 
 thofe where we really find comets, with the fame 
 exaclnefs as planets anfwer to thofe places in the 
 heavens, in which, according to calculation, they 
 ought to be. 
 
 The only difference to be found between thefe 
 new planets, and thofe firft known, is, firft, 
 that their orbits being much more excentric than 
 thofe of regular planets, and the Sun, on this ac- 
 count, being nearer one of their extremities, the 
 diftances of comets from the Sun are much more 
 various in the different parts of the orbits they de- 
 fcribe. Some few (fuch as that of i 680) approach 
 this ftar (the Sun) fo nearly, that in their perihe- 
 lion they are not a fixth part of his diameter dif- 
 tant from the Sun, and after this proximity they 
 recede to immenfe diftances, and to complete their 
 courfes, mount even beyond the regions of Saturn. 
 
OF COMETS. 21 
 
 From hence we may conclude, that if comets are 
 inhabited by living creatures, they muft be of a 
 temperament extremely different from ours, to 
 enable them to fupport all thefe viciflitudes. 
 
 Secondly, Comets employ a much longer time 
 than planets, in finifhing their revolutions round 
 the Sun. The floweft planet, Saturn, compleats 
 his courfe in 30 years ; while the fwifteft comet 
 employs 75 years for his : and it is highly probable 
 that the greateft number are many ages performing 
 their courfes. The length of their orbits, and the 
 flownefs of their revolutions, are reafons why we 
 have not yet been able to afcertain the return of 
 comets pofitively ; while planets never retire from 
 thofe regions within reach of mortal view; comets 
 appear only during that little part of their courfe 
 which they defcribe in the neighbourhood of the 
 Earth : the reft is performed in the mod diftant 
 regions of the heavens, during which time they are 
 loft to us : and when a comet returns, we have no 
 knowlege of it, but from fearching anterior re- 
 cords of comets which have appeared after equal 
 periods of time ; and by comparing the path of 
 that which appears, with the orbits of thofe, if we 
 are furniftied with fufficient obfervations of them 
 for that purpofe. It is by fuch methods that we 
 are encouraged to think the pec iod of the comet 
 which appeared in 1 682 to be about 75 years ; be- 
 
2'2 THE HISTORY 
 
 caufe we find a comet, which exhibited, in its mo- 
 tion, the fame phenomena, did appear in i 607, 
 in 1 53 1, and in 1456. Now it is more than 
 probable that all thefe comets were the fame; but 
 of this we (hall be more certain, if it appear again 
 in 1757 or 1758*. 
 
 From fimiliar reafons, but from an induction of 
 lefs weight, Dr. Halley conjectures the comets of 
 1661, and of 1532, to have been the fame, tak- 
 ing 129 years to compleat its revolution round 
 the Sun. 
 
 But Aftronomers have advanced ftill farther in 
 their refearches concerning the comet which ap. 
 peared in v 680, and find fuch a number of ap* 
 pearances after equal intervals of time, that they 
 very reafonable conclude its periodical revolution 
 round the Sun to be 57 5 years. 
 
 But what prevents thefe conjectures from having 
 the weight of certainty, is the want of precision in 
 thofe obfervations which were made by the ancients. 
 They applied themfelves rather to the events which 
 thefe ftars portended, than accurately to obferve 
 their places in the heavens. 
 
 We cannot depend upon any obfervations on 
 comets anterior to Tycho Brahe ; and till Newton 
 came, we had not the principles of the theory of 
 
 • See the articles 175a and nS9 in the following Effay. 
 
OF COMETS. 23 
 
 thefe fhrs. Time only, and a fufficient number 
 of observations, can perfect this theory. Labour 
 alone will be inefficient to attain that point of 
 knowlege, at which mankind are permitted to ar- 
 rive. It is a neceflary leflbn for them, and they 
 may be well allured that neither incefTant applicati- 
 on, nor even the moft fublime genius, can obtain 
 it ; they muft wait till a certain epocha of time 
 puts them in pofleflion of it. 
 
 Although the aftronomy of comets is (till far 
 from perfect, and though we cannot yet minutely 
 calculate their conrfe, we ought to be, however, 
 highly Satisfied with the exactnefs which confide- 
 rable parts of the path which comets take, can be 
 determined ; and as they are fubject. to the fame 
 law which moves the other celeftial bodies, as foon 
 as the comet appears, and has marked its orbit by 
 fome points in the heavens, where it has been ob- 
 served, we determine its courfe by the theory, and 
 the event has, to our wifhes, anfwered the calcu- 
 lation, in all thofe comets which have been care- 
 fully obferved, as far, and as long, as our fight 
 could follow them. 
 
 You will, perhaps, afk me, why then have we 
 not the full extent of the orbits that comets de* 
 fcribe, and the precife time of their return ? It is 
 not owing to any deficiency in the theory, but to 
 
* 4 the History 
 
 the fcarcity of obfervations, the imperfections of 
 our inftruments, and the debility of human fight. 
 
 The much extended ellipfes that comets defcribe, 
 approach fo nearly to parabolas, that in the part 
 of their courfe where they are vifible to us, there 
 is not any perceptible difference. It is with thefe 
 ftars as with vefTels, which we fee fet fail for long 
 voyages : from their fetting out, we can judge in ge. 
 neral, towards what region of the earth they may 
 be bound ; but we cannot have a certain know- 
 lege of what particular courfe they will fteer, un- 
 lefs we could fee them deviate from the track com- 
 mon to many countries *. 
 
 Thefe parts of the courfe, which comets defcribe, 
 when in our view, are common to ellipfes (which 
 are curve lines returning into themfelves) and to 
 parabolas, which extend to infinity ; in which cafe 
 there is no hopes of a comet's return : and we cal- 
 culate their places, as if they really defcribed thefe 
 laft mentioned curves; becaufe the points where 
 we find thefe comets are fenfibly the fame, and 
 their calculations are infinitely eafier. 
 
 * i. e. Their deviation from the common courfe, if feen, 
 would enable us to judge of the whole route. Thus Comets, 
 during the fhort time they are vifible to us, appear to move 
 in a parabola; but could our fight extend far enough to enable 
 us to fee them deviate from that track (and turn inwards) we 
 might then, from the information of our fenfes, conclude their 
 courfe to be in an (extremely excentrical) ellipfis. 
 
OF COMETS, 25 
 
 But if our fight could enable us to purfue co- 
 mets further, or if we could obferve them with 
 better inftruments, we mould fee them abandon the 
 parabolic route to follow the elliptic ; and be ac- 
 quainted with the extent of their ellipfes, and the 
 return of the ftars which defcribe them. 
 
 We cannot fufpect the truth of this theory, if 
 we examine the wonderful harmony, which is 
 found in the obferved courfes of many comets, 
 and thofe calculated by Sir Ifaac Newton *. I 
 fhall not therefore fpin out this letter with the 
 defpicable fyftems, which different aftronomers have 
 forged on the motion of comets: the opinions 
 of thofe who fuppofed them meteors were not 
 more ridiculous, and all their fyftems are as oppo- 
 (ite to reafon, as they are contradictory to expe- 
 rience. 
 
 The courfe of comets, once regulated, prevents 
 our regarding them as fnpernatural prefages, or as 
 flambeaux lighted up to menace the earth. But 
 while our fupcrior knowlege of comets, compared 
 with that of the ancients, exempts us from thefe 
 fears; it informs us that rhey may be the phyfical 
 caufe of very extraordinary events. 
 
 Almofr all the comets of which we have the bed 
 cbfervations, when they arrive in thefe regions of 
 
 • See Tables of the motions of feveral comets, in his Pan- 
 cipia, b. iii. prop. 41, and4z. 
 
 G 
 
26 THE HISTORY 
 
 the heavens, have approached much nearer the Sun, 
 than the earth ever does. They almofr all crofs 
 the orbits of Saturn, Jupiter, Mars, and the 
 Earth : and, according to the calculation of Dr. 
 Halley, the comet of 1680, pafled fo near the 
 orb of the earth, that on the 1 1 th of November, 
 it was only half the Sun's diameter diftant from 
 it. 
 
 H But, hitherto, none has threatened the earth 
 with a nearer appulfe than that of 1 680 ; for by 
 calculation I find that, Nov. 11, 1 h. 6 min. p. 
 m. that comet was not above the femidiameter of 
 the Sun to the northward of the way of the earth : 
 at which time, had the earth been there, the co- 
 met would have had a parallax equal to that of 
 the Moon, as I take it. This is fpoken to aftro* 
 nomers : but what might have been the confequen- 
 ces of fo near an appulfe, or of a contact, or laft- 
 ly of a fhock of the celeftial bodies, (which is by 
 no means impoffible to come to pafs) I leave to 
 be difcufled by the ftudious of phyfical matters *." 
 
 This great aftronomer has calculated the orbits 
 of 2 4 comets, of which we were furnimed with 
 fufficient obfervations ; and has found that thefe 
 ftars move in all directions ; having nothing in 
 common, but that their orbits are all defcribed 
 round the Sun. 
 
 • Phil. Tranf. N°. ap?- 
 
OF COMETS. 27 
 
 A great fettof philofophers* held, that the ce- 
 leftial bodies of our fyftem had no other motion 
 than that of being carried away in a vaft vortex of 
 fluid matter round the Sun. Their opinion was 
 founded upon this : that the motions of the planets 
 are all in the fame direction as that of the Sun, 
 round its own axis. Though the fa£t is true in 
 general, yet the planets do not fo ftriftly follow 
 this direction as they muft do, if impelled by the 
 general motion of vortices. They would then all 
 move in the fame plane, which would be that of 
 the ecliptic, or at leaft in planes parallel to the 
 ecliptic ; but they do neither, which has greatly 
 embarraffed thefe philofophers. 
 
 A great man f has attempted to account for 
 this obliquity in the courfes of planets, with ref- 
 -peft to the plane of the ecliptic ; and we muft ad- 
 mire the refources, and wonderful fagacity he has 
 difcovered, in defending the vortices againft this 
 objection. But comets form an invincible obfta- 
 cle to this vortex ; they not only deviate from the 
 common road, but move freely in all directions: 
 fome following the order of the flgns in a plane, 
 very little inclined to the plane of the ecliptic : o- 
 thers in planes which are almoft perpendicular to 
 
 * Cartefiam. 
 t Mr. John Bernoulli, in his differtation concerning the 
 Inclination of the orbits of the planets. 
 C 2 
 
28 THE HISTORY 
 
 it : and fome there are, whofe motion is intirely 
 retrograde, which move in an oppofite direction to 
 that of the planets, and of thefe pretended vortices ; 
 which can only be done by thefe ftars moving a- 
 gainft an extremely rapid torrent, without fufFer- 
 ing the leafl: retardation. But thofe who believe 
 this poffible may make the experiment by rowing 
 in a boat againff the current of a river. 
 
 I know fome aftronomers have believed that the 
 retrograde motion of comets might not be fuch in 
 fact, but in appearance ; and be in reality direct, 
 as the motions of the planets are in fome fituations 
 with refpect to the earth. This might be credit- 
 ed, if we were permitted to difpofe of comets as 
 we mould judge convenient on this or that fide 
 the Sun ; and if, thus placed, they were capable 
 ofanfwering equally to the neceiTary laws of moti- 
 on in the heavenly bodies. But this matter being 
 well examined, and calculated, as it has been by 
 Sir Ifaac Newton and Dr. Halley, we find the im- 
 pofTibility of placing comets juft where partiality 
 for vortices would require ; and we are reduced to 
 the neceflity of acknowleging them to be really 
 retrograde. In this variety of motions, it is poflt- 
 ble that a comet may meet with a planet, in its 
 courfe, nay, with our earth ; and, if we mould t er be 
 fo circumftanced, it is but natural to expert the ar- 
 rival of fome terrible accident. The mere approach 
 
OF COMETS. 29 
 
 of thefe bodies to each other would, no queftion, 
 occafion great changes in their motions, whether 
 by the attraction they would reciprocally exercife 
 on each other, or by fome fluid comprefied be- 
 tween them. The leaft of thefe motions, rauft 
 inevitably change the fituation of the axis and 
 poles of the earth. That part of the globe which 
 was formerly towards the equator, after fuch an 
 accident, would be found near the poles ; and that 
 which was heretofore near the poles, we fhould- 
 find near the equator. 
 
 The approach of a comet might produce con- 
 ferences (till more fatal ; I have not yet menti- 
 oned their tails, which have been as productive 
 of abfurd notions, as any thing relative to comets ; 
 but the moft probable opinion is, that they are 
 immenfe torrents of exhalations and vapours forc- 
 ed from them by the ardent heat of the Sun. The 
 ftrongeft proof of this is, that the tails of comets 
 are only vifible when pretty near the Sun, that 
 their fize increafes in proportion to their approxu 
 mation to it, and decreafe, and are diffipated, when 
 they are diftant from ir. 
 
 A comet, accompanied by a tail, might pafs fo 
 near the earth, as to drown it in the torrent that 
 it draws after it ; or in an atmofphere cl the lame 
 nature of that with which it is furrounded. The 
 Comet of 1 68o, which wasfo near the Sun, fu- 
 C 3- 
 
3 o THE HISTORY 
 
 ftatned a heat 28,000 times greater than that of 
 the earth in fummer. Sir Ifaac Newton, in the 
 various experiments he has made upon the heat 
 of bodies, having calculated the degree of heat 
 which this comet muft have acquired, found it 
 would be 2,000 times hotter than red hot iron ; 
 and that a globe of red hot iron, of the llze of 
 the earth, would be 50,000 years in cooling. 
 What then muft we think of the heat which yet 
 remained in that comet, when, returning from 
 the Sun, it crolTed the orbit of the earth ? Had it 
 palled nearer, the earth muft have been reduced to 
 afhes, or vitrified; or, if the tail only had reach- 
 ed us, the earth would have been drowned in li- 
 quid flame ; in the fame manner as we fee a 
 kingdom of ants perifh by the boiling liquor which 
 the labourer pours upon them. 
 
 An ingenious author has made fome very ilngu* 
 lar and daring enquiries, concerning that comet 
 which was expected to burn the earth * : tracing it 
 back from 1 680, (the time when it laft appeared) 
 he finds a comet in 1106, another in 531 or 
 532 . and one at the death of Julius Caefar, forty- 
 four years before our Saviour : this comet is, with 
 great probability, fuppofed to be the fame, and 
 performs ts revolutions in $j 5 years ; and the fe- 
 
 * A new Theory of the earth by "Whiftop. 
 
OF COMETS. 31 
 
 venth period back from 1 680, correfponds with 
 the year of the univerfal deluge. After what has 
 been faid, we may eafily conjecture in what man- 
 ner the author may explain every circumftance of 
 this great event. The comet in its way to the Sun, 
 paffing near the earth, drowned it with its tail and 
 atmofphere, which had not then acquired the de- 
 gree of heat which we have jnft mentioned, and 
 caufed the rain of forty days which is mentioned 
 in the hiftory of the deluge. But Whiiton, from 
 the approach of this comet, drew ftill another con- 
 fequence, which exactly agrees with the manner 
 in which the divine writings have taught us to 
 believe the deluge happened. The attraction 
 which the comet and earth reciprocally exercife 
 on each other, changed the figure of the latter ; 
 and drawing it towards the comet, let out the fub- 
 terraneous waters, by breaking open the fountains 
 of the great abyfs. The fame author has not only 
 attempted in this manner to explain the deluge, 
 but believes that, fome time or other, a comet, 
 mod probably the fame, will, as it returns from 
 the Sun, fhed burning and mortal exhalations on 
 us, and occafion to the inhabitants of the earth all 
 the misfortunes which are predicted' to it, at the 
 end of the world ; and caufe, in (hort, the con- 
 flagration which is to confume this unfortunate 
 planet. 
 
32 THE HISTORY 
 
 However bold his thoughts may be, they at 
 Ieaft contain nothing contrary either to reafon, re- 
 velation, or morality. God made ufe of the de- 
 luge to exterminate a race of men, whofe crimes 
 merited chaftifement ; and will probably, one day 
 or other, in a dill more terrible manner, deflroy 
 without exception all human kind ; but he may 
 have configned the effects of his anger to phyfical 
 caufes ; for he, who is the great Creator and Mover 
 of each celeftial body in the univerfe, may have 
 regulated the courfes of them all in fuch a manner, 
 as to produce thefe great events in the fullnefs of 
 time. 
 
 Though you mould not be convinced, madam, 
 that the deluge and conflagration of the earth de- 
 pend upon the comer, at leaft you will confefs that 
 its appulfemay occafion fome fuch accident. Gre* 
 gory, one of the greateft aftronomers of the age, 
 has fpoken in fuch a manner of comets, as would 
 re eftablirti them in all their former terrors. This 
 great man, who has contributed fo much to the 
 perfecting the theory of thefe ftars, in one of the 
 corollaries of his excellent work, fays, < Hence, 
 « alfo it follows, that if the tail of a comet mould 
 < touch the atmofphere of our earth, (or if a part 
 f-. of this matter fcattered and diffufed about the 
 6 heavens mould fall into it) the exhalations of it 
 J mixed with our atmofphere, (one fluid with a* 
 
OF COMETS, 33 
 
 « nother) may caufe very fenfible changes in our 
 1 air, efpecially in the animals and vegetables: for 
 
 * vapours, as they call them, brought from ftrange 
 1 and dittant regions, and excited by a very in- 
 ' tenfe heat, may be very prejudicial to the inha* 
 
 * bitants, or produces of the earth ; wherefore 
 ' thofe things, which have been obferved by aH 
 1 nations, and in all ages, to follow the appari- 
 
 * tions of comets, may happen : and it is a thing 
 
 * unworthy of a philofopher, to look upon them 
 « as falfeand ridiculous"*.' 
 
 A comet palling near the earth might fo alter its 
 motion, as even to change it into a comet ; and 
 inftead of continuing its prefent courfe in an unl* 
 form mild climate of a temperature adapted t*> 
 man, and the different animals which inhabit it, 
 the earth would be expofed to the greateft vicilTi* 
 tudes, fcorched in its perihelion, or frozen by 
 the cold of the utermoft regions of the heavens : 
 proceeding thus from one evil to another, till per- 
 haps another comet again changes its courfe, and 
 reinftates it in its original uniformity. 
 
 Another misfortune might ftill poflibly befal the 
 planet which we inhabit; for if a great comet 
 mould advance too near the earth, it might force 
 it from its orbit, and oblige it to perform its fu* 
 
 * Gregory, Aftron* Phyfic. lib, v. corol. ii. prop. 4. 
 
34 THE HISTORY 
 
 ture revolutions round the comet; wholly fubjeft- 
 ing it either by its attraction, or, if I dare ufe the 
 word, by involving it in its vortex : the earth, 
 thus become a fatellite to the comet, would be 
 carried by it into thofe diftant regions which it vi- 
 sits. Wretched condition for a free born planet, 
 which has fo long enjoyed a temperate fky ! In 
 fbort, the comet might in like manner rob us of 
 our moon ; and were we to efcape upon fuch eafy 
 terms, we might think ourfelves very well off. 
 But the molt violent accident that could befal us, 
 would be the percuffion, or (hock of a comet a- 
 gainft our globe, which might break both itfelf 
 and the earth into a thoufand pieces. In fuch 
 cafe, doubtlefs, both thefe bodies would be de- 
 frayed ; and gravity would immediately form one 
 or many planets out of them. If the earth has 
 never yet undergone thefe cataftrophes, it has 
 doubtlefs experienced many great changes. The 
 prints of fifties, and even petrified fifties, which 
 we find in places very diftant from the fea on the 
 very fummit of the higheft mountains, are incon- 
 tellable medals of fome one of thefe events. 
 
 A lefs violent fhock, fuch as would not en- 
 tirely break our planet, would certainly caufe great 
 changes in the fituation of lands and feas ; the 
 waters during fuch an accident would be greatly 
 raifed in fome parts, and would drown vaft regions 
 
OF COMETS, 35 
 
 of the furface of the earth, from which they would 
 afterwards fubfide. To fuch a mock as this Dr. 
 Halley attributes the deluge : the irregular difpo- 
 fition of the beds of different kinds of matter 
 which compofes the earth ; the enormous moun- 
 tains, much more refembling the ruins of an an- 
 cient world, than one in its primitive (late; all 
 concur in giving weight to his opinion. Thisphi- 
 lofopher conjectures, that the exceflive cold we find 
 in the north-well: parts of America, which is fo 
 little proportioned to the prefent latitude of thofe 
 places, is the remains of cold in thofe countries 
 which were formerly fituated nearer the poles; and 
 that the prodigious quantities of ice which we at 
 prefent find there, is the remains of that by which 
 they were formerly covered, and which is not yet 
 entirely melted. 
 
 It is evident that, whatever may befal the earth f 
 the other planets are equally liable to ; unlefs the 
 enormous fize of Jupiter and Saturn mould be 
 their protection from the infults of comets. It 
 would be a very curious fight for us to behold a 
 comet approach, and fall upon Mars, Venus, or 
 Mercury ; and either break it into pieces in our 
 view, or violently carry it away, in order to make 
 it a fatellite. 
 
 Comets may even attempt the fun himfelf ; and 
 though they have ' not fufficient power to draw 
 
3^ THE HISTORY 
 
 -him after them, yet their magnitude and near ap» 
 jxoach might enable them to remove him from 
 his prefent place. But Newton fecures us from 
 fuch a removal, by a conjecture drawn from the 
 known analogy between comets and planets. 
 Amongft thefe laft, the leaft are fituate neareft the 
 Sun, and the greateft are mod diftant. 
 
 Newton conjectures that it is the fame with 
 comets; that the leaft only approach very near 
 this ftar, and the great ones are kept at the great- 
 eft diftances*; left, fays he, they mould difturb 
 the Sun by their attraction. But is it neceflary for 
 the fyftem, that the Sun mould not be difturbed : 
 Ought he alone to enjoy this prerogative ? Or, ra- 
 ther, is it one ? If we confider the celeftial bodies 
 as material maftes only, is their immobility a per- 
 fection ? is not their motion, at leaft, as defirable 
 as reft ? Or fhould we regard them as capable of 
 fentiment, is it unfortunate for me that another 
 has the afcendancy . ? Is not the fate of him who 
 is attracted as defirable as his who attracts ? 
 
 You will allow, madam, that comets are not fo 
 devoid of importance as they at prefent are gene- 
 rally believed. Every thing evinces them able to 
 produce moft deftructive changes, both to our 
 earth, and to the whole folar fyftem ; from the 
 
 * Philofoph. Nat. Princip. Mathemat. lib. iii. prop. 4T. 
 
OF COMETS, 37 
 
 dread of which habit only fecures us. But after 
 all, we have great reafon to think ourfelves fafe 
 from fuch calamities as thefe juft mentioned ; for 
 the earth being but a point in the immenfity of 
 fpace, and our lives of fo very tranfient duration, 
 joined to our certain knowlege that in fo many 
 thoufand years no accident of this kind has ever 
 happened to the earth ; all thefe confiderations 
 are fufficient to prevent our apprehenfions of being 
 -either witneffes, or victims, to any fuch in future. 
 Thunder, however terrible, is but little to be 
 feared by each individual, by reafon of the fraall 
 fpot he engrofles in that fpace where the thunder 
 may fall. It is the fame with the little point we 
 fill in the vaft duration of time in which thefe im- 
 portant events happen. But though thefe confi- 
 derations annihilate the danger to us, yet they 
 cannot alter its nature. 
 
 But ftill the confideration that a common mif- 
 fbrtune is fcarcely any misfortune at all, ought to 
 banifh our fears ; for the mortal who mould un- 
 fortunately be of a conftitution too robuft, and 
 who mould folely furvive the accident which had 
 deftroyed the whole human race, would have the 
 greateft caufe of complaint. King of the whoL 
 earth, pofTeflbr of all its treafures, he would lan- 
 guifh with grief and forrow ; and his whole life 
 would not be worth the laft moment of him who 
 D 
 
38 THE HISTORY 
 
 expired with what he loved. But I fear I have 
 railed too much at comets ; though I cannot re- 
 proach myfelf with injuftice towards them, as they 
 are really capable of occafioning every cataftrophe 
 to us that I have mentioned : however, I will 
 make them all the reparation I can, by pointing 
 out to you the advantages they may poflibly pro- 
 cure us ; though I very much doubt your being fo 
 fenfibly touched by the hopes of thefe advantages, 
 as alarmed by the fear of changing a ftate in which 
 you have hitherto fpent your time fo agreeably. 
 Our earth has kept the fituation it now holds in 
 the heavens thefe five or fix thoufand years, dur- 
 ing which time its feafons have been the fame, and 
 climates diftributed as we now fee, and with which 
 we ought to be very well contented, without 
 afpiring at a milder fky, or perpetual fpring. 
 
 Nothing, however, would be more eafy than 
 for a comet to procure us thefe felicities. Its ap- 
 proach, whkh, as we have mown, might caufe fo 
 many diforders, might alfo render our condition 
 much better. I ft. By occafioning a little change 
 in the fituation of the earth ; it might elevate its 
 axis, and fix our feafons to a continual fpring. 
 2dly, A flight remove of the earth in the orbit 
 fhe defcribes round the Sun, would make her de- 
 (bribe one more circular, in which me would always 
 be equi-diftant from the ftar from which fhe re* 
 
OF COMETS, 39 
 
 ccives both heat and light. And, 3«dly, though 
 it was obferved above that a comet might ravifli 
 our Moon from us, yet on the other hand, a fmall 
 comet might be reduced to a lunar (late itfelf, 
 and be both condemned to make its revolutions 
 round us, and to illuminate our nights. It is ve- 
 ry pomble that our Moon was originally a little 
 comet, which advancing too near the earth, was 
 taken captive by it, and reduced to a ftate of fer- 
 vitude. Jupiter and Saturn, whofe magnitudes are 
 much greater than that of the earth, and whofe 
 power extends further, and over larger comets, 
 can make fuch aequifitions with greater facility 
 than the earth : hence perhaps it is, that Jupiter 
 has four moons to attend him, and Saturn five ; 
 and though we have feen above how dangerous 
 the mock of a comet might prove, yet the mifchief 
 may be fo inconsiderable, as to be fatal only to 
 that part of the globe which receives the blow ; we 
 might perhaps efcape with the crufh only of one 
 kingdom, while the reft of the earth would enjoy 
 thofe rare productions with which fo great a tra- 
 veller would prefent them. We mould be great- 
 ly furprifed, perhaps, to find the fragments of 
 thefe (o much defpifed maffes compofed of gold 
 and diamonds : but it is hard to fay whofe amaze- 
 ment would be the greater, at our firft meeting ; 
 ours, or thofe inhabitants of the comet which the 
 D 2 
 
40 THE HISTORY 
 
 mock might throw upon the earth ? "What figures 
 would each party think the other ? 
 
 But there is ftill another means of enriching our- 
 felves from the fpoils of comets. In the difcourfe 
 concerning the figure of the flars, it has been ex- 
 plained how a planet might appropriate to itfelf 
 the tail of a comet ; and,, without either drowning 
 its inhabitants, or poifoning them by noifome va- 
 pours, might form it into a fort of ring or vault, 
 fufpended round it on every fide. It has been 
 mown, that the tail of a comet might be fo cir- 
 cumftanced, as that the laws of attraction would 
 oblige it in this manner to furround the earth : 
 the form of thefe rings has been determined, and 
 the whole anfwers fo well to what is obferved round 
 Saturn, that it feems rather difficult for a more 
 probable, or natural account of this phaenomenon 
 to be difcovered ; we muft not therefore be afto- 
 nifhed, if one day or other we fhould fee a like 
 appearance round the earth. 
 
 Newton, in his reflections on the courfes of 
 comets through aH the regions of the heavens, 
 and the prodigious quantity of vapours they drag 
 after them, confers upon them an employment 
 which is not perhaps the mofl honourable of any 
 in the fyftem : he fuppofes that they carry water 
 and humidity to repair the lolTes of the other ce* 
 leftial bodies. Such a fupply may perhaps be 
 
OF COMETS, 41 
 
 needful to the planets, but it would infallibly be 
 fatal to their inhabitants, as thefe foreign fluids 
 would differ too much from our own not to be 
 noxious. They doubtlefs would infect both air 
 and water ; and the greateil number of inhabi- 
 tants would perifh. But nature often facrifices 
 fmall objects to the general good of the univerfe. 
 Another ufe of comets may be, to repair the 
 lofles which the Sun fuftains, by the continual e- 
 miflion of the matter of which it is formed. When 
 a comet paiTes fo near it as to penetrate the very 
 atmofphere which furrounds it, this atmofphere 
 being an obilacle to its motion, and a check to 
 its velocity, mult confequently alter the figure of 
 its orbit, and contract the diftance of its perihelion. 
 And this diftance conftantly diminifhing at each 
 return of the comet, it muft, after a certain num- 
 ber of revolutions, fall into that immenfe fire (the 
 Sun) to which it will ferve ;ur new aliment : for 
 thofe vapours and atmofpheres which would 
 drown planets, art incapable of extinguifhing the 
 Sun. 
 
 What thefe comets perform which move round 
 our Sun, thofe may likewife perform which move 
 round other funs, (the fixed liars) and may relu- 
 mine ftars which are nearly extinguished. But this 
 is one of the leaft benefits we may derive from 
 comets. And now, madam, I have nearly com- 
 D 3 
 
42 THE HISTORY 
 
 municated to you my whole cometary knowlege. 
 A time will come, perhaps, when we fhall all be 
 wifer upon the fubject : for Newton's Theory, 
 which has enabled us to determine the orbit of co- 
 mets, will in time conduct us to the exact period of 
 their revolutions. 
 
 But it will not be amifs to inform you, that al- 
 though thefe liars, while they are vifible to us, are 
 governed by the fame laws as the other planets, 
 and are like them fubjecT: to calculation, yet we 
 cannot be afTured of feeing them return at the ex- 
 act time afligned them, or in exactly the fame or- 
 bits. The many accidents they may encounter in 
 their way, fuch as paffing by the atmofphere of 
 the Sun, or meeting with planets, or other comets, 
 may fo alter their courfes, that after a few revolu- 
 tions, we (hall no longer be able to know them 
 again. 
 
 I have fpoken of almoft every comet, except 
 that which appears at prefent ; for this plain rea- 
 fon, becaufe I have but little to fay about it. This 
 comet, which makes fo much noife, is one of the 
 rooft contemptible that ever appeared. Some have 
 been fecn whofe apparent magnitude equalled that 
 of the Sun ; many whofe diameters appeared a 
 fourth or fifth part of his diameter. Others, again, 
 have mown with various and vivid colours ; fome 
 have appeared of a frightful red, many of a gold 
 
OF COMETS, 43 
 
 colour, and others inveloped in thick fmoke ; and 
 fome few have been faid to have diffufed a fulphu- 
 rous fmell even down to the very earth. The 
 greateft number drew tails of an enormous length 
 after them ; and the comet of i 680 had one which 
 filled near half the heavens. 
 
 This comet appears only as a ftar of the third or 
 fourth magnitude, and has a tail of between four 
 and five degrees. It was discovered by Mr. Grant, 
 the 2d of March, at the foot of Antinous. 
 
 If you wifh for more fcience in this fubjecl, with 
 a fucceflion of obfervations, made with the moft 
 finifhed accuracy, you will meet with them in that 
 excellent work of M. le Monnier, called the The- 
 ory of Comets. 
 
 In the mean time, you will, I hope, be fatisfied 
 with knowing that this comet has paffed from An- 
 tinous into the Swan, and from the Swan into 
 Cepheus, with fuch rapidity, that it fometimes ran 
 fix degrees in twenty-four hours. It proceeds to- 
 wards the pole, and is not above ten degrees from 
 it. But it abates of its fpeed ; and its light and 
 tail are fo diminished, that we perceive it moves 
 from the earth ; and that for this time, we have 
 nothing either to hope, or to fear from it. 
 
 faris, March jtf, 
 • 74*. 
 
A N 
 
 ESSAY 
 
 TOWARDS A HISTORY OF 
 
 The PRINCIPAL COMETS 
 
 THAT HAVE 
 
 Appeared fince the Year 1742. 
 
ADVERTISEMENT. 
 
 TH E following eflay is intended for the ufe 
 of fuch only as give mathematicians credit 
 for their calculations of the orbits, or paths of co- 
 mets in the heavens; and who, (taking it for grant- 
 ed that thefe calculations are juft) wifh to gratify 
 their curiofity, as well with regard to the refult of 
 mathematical demonftrations, as to the phaenome- 
 na, andmort interefting particulars of thefe erratic 
 iters. 
 
 An aftronomer, armed at all points with Theo* 
 rems, Problems, Corollaries, Lemmas, and Scholia, 
 is a very formidable being, and equally inacceilible 
 to the generality of mankind, with the fters about 
 which he writes. And yet, without thefe terrible 
 arms to defend him from ignorance and preemp- 
 tion, his fcience would degenerate into judicial 
 aftrology, and he would be little better than a jug- 
 gler or a fortune teller. It is therefore intended 
 in fketching out the following little hiftory of co- 
 mets, to fave the reader the expence of purchafing, 
 and trouble of perufing a great number of difficult 
 and dry treatifes, and to give him the fum and 
 fubftance of fuch difcoveries and conclufions, as 
 have proceeded from the moft laborious and ope- 
 rofe calculations, to which human intelligence can 
 
( 48 ) 
 
 reach. And it fhould be remembered, that tho' 
 the foregoing letter is written in a familiar and 
 fportive (Vile, and accommodated to the perception 
 of the ladies, and fuch as are nnfkilled in mathe- 
 matics, yet it is founded on true fcience : the 
 author having been among the firft, and molt able 
 geometricians, who adopted and explained the 
 Newtonian philofophy in France, and who, by 
 his journey to the polar circle, in order to mea- 
 fure a degree, has proved and illuftrated it, by 
 afcertaining the figure of the earth to be juft what 
 our great countryman had always fuggefted it to 
 be. 
 
THE 
 
 HISTORY 
 
 O F T H E 
 
 PRINCIPAL COMETS 
 
 That have appeared fince the Year 
 
 1742. 
 
 IN the preceding letter it has been remarked, 
 that Dr. Halley upon the Newtonian theory, 
 had determined the elements of twenty-four co- 
 mets*. At prefent the number of thofe that have 
 been accurately obferved, and whofe orbits are cal- 
 culated, is more than doubled. A particular de- 
 tail of fuch as are moft interefting may therefore 
 be acceptable to our readers. We (hall, however, 
 only juft mention the comets of 1 702, 1706, 
 
 * The elements of a comet are the five articles which deter- 
 mine the pofition and magnitude of the parabola itde^cribes, 
 and which conftitute its theory; namely, its node, inclination, 
 placeof its perihelion, perihelion diftance, which isthefquare 
 of the parameter, and the time when the comet arrives at its 
 perihelion. 
 
 E 
 
50 THE HISTORY 
 
 and i 71 8, whofe elements different aftronomers 
 have determined by the Newtonian method ; but 
 fhall be a little more particular about that of 1 729. 
 A comet rendered very lingular, if not by its bril- 
 liancy, at leaft by other circumftances. It was 
 firft perceived at Nifmes, by father Sarabel, a 
 Jefuit, July 31, between Canis Minor and the 
 Dolphin ; it was fo fmall and dull, that during 
 moon light, it was fcarce vifible; however, this 
 father informed Caffini and the academicians of 
 if, who obferved it from the ift of Auguft till the 
 2 I ft of January '730, when it difappeared. Their 
 obfervations are publifhed in the memoirs of the 
 academy of fciences for the year 1 7 30, and after 
 them Maraldi, in 1742, has calculated the pa- 
 rabolic trajectory, which it defcribed. Many other 
 aftronomers have done the like, as the Abbe de la 
 Caille, M. de Lille, Mr. Kies, aftronomer at 
 Berlin, M. Struick, &c. It paffed between the or- 
 bit of Mars and that of Jupiter, but much nearer 
 the latter ; hence it was always fo fmall and mov- 
 ed fo flow, (for it hardly advanced an eighteenth 
 of a degree in the fix months it was obferved) ; at 
 firft its motion was direct, and then retrograde, 
 like the fuperior planets. Calculation agreed fo 
 well with thefe obfervations, that though they a. 
 mounted to fifty, the difference in longitude ex- 
 
OF COMETS, 51 
 
 ceeds not three minutes, and in latitude only a 
 few feconds. 
 
 We {hall pafs over the comet of 1737 calcu- 
 lated in the Philosophical Tranfattions, N° 446: 
 that of 1 7 39, of which feveral aftronomers have 
 given the elements ; and come to that of 
 
 1742. This comet, notwithftanding M. de 
 Maupertuis thinks it fo contemptible, was obferved 
 by Mr. Betts at Oxford, who fuppofed its magni- 
 tude to be, at leaft, equal to that of the earth. 
 
 1 743. Two comets appeared this year. The 
 fir ft was obferved by M. Struick, the fecond by 
 Mr. Klenkenberg ; but both were fmall and offer- 
 ed no remarkable phenomena to common obfer- 
 vers. 
 
 1744. The comet which appeared this year, 
 was firft feen in England, at the obfervatory of 
 the Earl of Macclesfield, December 2 3, 1 743. It 
 feems to have been accurately obferved at Oxford 
 by the reverend Mr. Betts, who, in his journal, 
 January 2 3, 1 744, fays, * The comet this even- 
 < ing appeared extremely bright and diftin£t, and 
 c the diameter of its nucleus, nearly equal to that 
 * of Jupiter, its tail extending above fixteen de- 
 ' grees from its body; ' and adds, « That on Fe- 
 1 bruary 23, the prodigious brightnefs it acquired, 
 i by its near approach to the fun, made it vifible 
 1 in the day time.* The nodes of this comet, and 
 E 2 
 
53 THE HISTORY 
 
 the planet Mercury, were fituated within lefs than 
 half a degree of each other ; which gave rife to a 
 report that the comet carried Mercury from its 
 orbit: but, fays Mr. Betts, f Upon computing 
 
 < their heliocentric conjunction, which happened 
 
 < February i 8, I found the comet was, at that 
 1 time, diftant from Mercury nearly one third part 
 c of the great circle; being twice as near the Sun, 
 
 < as the planet Mercury.* This was the mod 
 confiderable comet that had appeared fince the 
 year 1680. 
 
 M. des Chezeaux (EiTais de Phyfique 1751) 
 obferves, that at its firit appearance, it had no 
 tail, at leaft perceptible to the naked eye ; but in 
 approaching the Sun, it acquired one which in- 
 creafed every day till it arrived at its perihelion ; 
 fo that February the 1 7 th, it was forty degrees long, 
 and it frill augmented confiderably after the peri- 
 helion ; for though the body of the comet could 
 no longer be feen, the tail was vifible two hours 
 before fun rife, 20 or 30 degrees above the ho- 
 rizon, while the body was below it. According to 
 this author, the tail was divided into five large 
 itreams, or bands, and mult have afforded a ftrange 
 fpettacle, if the earth had been at that time in a 
 favourable pofition for obferving it. This comet, 
 and that of 1 742, gave rife to feveral learned and 
 ingenious works. Soon after M. de Maupertuis' 
 
O F C O M E T S. S3 
 
 letter, came out the theory of comets by M. le 
 Monnier, 8vo. in which, befides the tranflation of 
 Halley's Synopfis, is included an introduction and 
 hiftorical fupplement concerning the progrefs of this 
 theory, before and fince Newton's time ; together 
 with divers intereding particulars relative to the 
 catalogue of the fixed ftars, and theory of the Sun: 
 the treatifeof M. desChezeaux, mentioned above: 
 OfTervazioni intorno lacometa dell anno i 744, or 
 obfervations concerning the comet of 1 744 by Za^ 
 notti, profeilo]'at Bologna ; and an excellent trea- 
 tife by the celebrated Euler, called Theoria Mo- 
 tuum Planetarum et Cometarum, or Theory of 
 the motions of Planets and Comets, &c, &c. 
 
 1746. The comet of this year was firft obferv- 
 ed at Laufanne, Auguft 1 3, by M. des Chezeaux; 
 and was feen afterwards by many other afrrono- 
 mers. It was then proceeding to its perihelion, 
 to which it arrived not before February 8, 1 747. 
 1748. M. Struick informs us, (Philofophical 
 TranfacYions) A$J in the month of May, this year, 
 three comets witu.vifible, both at Amfterdam, and 
 in other parts of Europe, on the very fame night; 
 of which there is no other in fiance in hiftory: one 
 of them was obferved by F. Hallerftein, at Pekin 
 in China, from April 26, to June 18 who fays 
 (Philofophical Taranfactions abridgedj vol. x.) 
 { The comet feen by us this year was very difmal, 
 E 3 
 
54 THE HISTORY 
 
 ' for befides its mining with a very obfcure and 
 
 < malignant light, it went in fo defert a path, and 
 ' in fuch an unfavourable fky, that it could be 
 
 < obferved but very feldom, and be compared with 
 1 but a few fmall ftars not well known.' 
 
 1757. It is remarked by M. Montucla (Hi- 
 ftory of Mathematics) that near ten years had e- 
 lapfed fince any comet had appeared. A very un- 
 common circumfrance, if we may judge by the 
 frequency of thefe phenomena for fome centuries 
 paft, fince comets have been fonaiiowly watched. 
 The comet of this year, however, came kindly 
 to relieve our impatience. It was accurately ob- 
 ferved by Dr. Bradley, from September 12, to 
 October 1 1 , and again on the 1 8th and 19th of 
 the fame month. " When I firft difcovered this 
 comet (fays the doctor, Philofophical Tran factions, 
 vol. i.) it appeared to the naked eye like a dull 
 ftar of the fifth or fix magnitude ; but viewing it 
 through a feven foot telefcope, I could perceive 
 a fmall nucleus, (furrounded, as yfual, with a ne- 
 bulous atmofphere) and a fhort (t J, extending in 
 a direction oppofite the Sun." 
 
 " It kept nearly at the fame diftance from the 
 earth for about ten or twelve days together, after 
 I firft faw it ; but its brightnefs gradually increaf- 
 ed then, becaufe it was going nearer to the Sun. 
 Afterwards, when its diftance from the earth in- 
 
O F G O M E T S. $5 
 
 creafed, though it continued to approach the Sun, 
 yet its luftre never much exceeded that of ftars of 
 the fecond magnitude ; and the tail was fcarce to 
 be feen by the naked eye." 
 
 The elements the doctor has given of this co- 
 met (adapted to Dr. Halley's general table for the 
 motion of comets in parabolic orbits) will be fuf- 
 ficient to enable future aftronomers to diftinguifh 
 it upon another return ; but as they do not cor- 
 refpond with the elements of the orbit of any o- 
 ther comet hitherto taken notice of, we cannot at 
 prefent determine its period. 
 
 This comet was likewife obferved by Mr. Klen- 
 kenberg at the Hague, who in a letter to Dr. Brad- 
 ley fays, " It appears very evident not only from 
 my calculation, but from every other circumftance 
 of this comet, that it is not the fame with that of 
 the year I 682, which on certain accounts is very 
 defirable to be known ; for both here, and' in 
 other parts of the Netherlands, there have been 
 fome people who have publifhed mere conjectures; 
 and have ventured (very minutely and exactly, as 
 they pretended) about the time that this comet 
 firft appeared, to predict the return of that of 
 1 682 : but by the above obfervations the weak- 
 nefs of their pretentions is evident ; whereas, if 
 this had proved to be the expected comet, they 
 would have afTumed to themfelves much undue 
 
5 6 THE HISTORY 
 
 praife, and have pretended to knowlege even fupe- 
 rior to the everywhere much celebrated Newton, 
 and Halley." 
 
 1758. Aflronomers were much difappointed 
 this year in not finding Dr. Halley's prediction ful- 
 filled : who in his Synoplis of comets has thefe 
 words,— " and indeed there are many things which 
 make me believe that the comet which Appian ob- 
 ferved in the year 1531, was the fame with that 
 which Kepler and Longomontanus took notice of 
 and defcribed in the year 1 607, and which I my- 
 felf have feen return and obferved in 1682. All 
 the elements agree, and nothing feems to contra- 
 dict this my opinion, bcfides the inequality of the 
 periodic revolutions : which inequality is not fo 
 great neither, as that it may not be owing to phy- 
 Ileal caufes. For the motion of Saturn is fo di- 
 fturbed by the reft of the planets, efpecially by 
 Jupiter, that the periodic time of that planet is un- 
 certain forfome whole days together. How much 
 more therefore will a comet be fubject to fuch like 
 errors, which riles almoft four times higher than 
 Saturn, and whofe velocity, though increafed but 
 very little, would be fufficient to change its orbit 
 from an elliptical to a parabolic one. However, 
 I am further confirmed in my opinion of the co- 
 mets which appeared at the above periods, being 
 the fame -, and let me alfo add, that in the year 
 
OF COMETS. 57 
 
 1456, in the fummer time, a comet was feen 
 palling retrograde between the Earth and Sun, 
 much after the fame manner : which, though no- 
 body made obfervations upon it, yet from its pe- 
 riod, and the manner of its tranfit, I cannot think 
 different from thofe I have juft mentioned. 
 Hence I dare venture to foretel that it will return 
 again about the year 1 758." 
 
 As this is a point, and a period, of equally 
 great importance in aftronomy, we mud not pafs 
 them over too haftily. Mr. Barker in a letter to 
 Dr. Bradley, 1.755 (inferted in the Philofophical 
 TranfacYions of that year) has given, in twelve 
 fhort tables, the apparent path of this comet, fup- 
 pofing its perihelion any month in the year, with 
 its accurate difrance from the earth. But as no 
 allowance was made for the difturbance this co- 
 met might have met with, either from the planets, 
 or other comets, in its path, it did not return 
 within the period for which his tables were con- 
 {trucked. 
 
 But while all the world was big with expecta- 
 tion, and aitronomers had turned night into day, 
 in hopes of the accomplishment of that prediction 
 which was to confirm their favourite theory : while 
 fcoffers began to triumph in the hope that thefe 
 ftar-gazers were no greater conjurors than them- 
 felves ; and while the friends to fcience began to 
 
58 THE HISTORY 
 
 tremble for the event : the profound and indefa- 
 tigable M. Clairaut, one of the famous academi- 
 cians who accompanied M. de Maupertuis in his 
 voyage to the polar circle, remembering D. Halley 
 had fuggefted that it was poilible for the comet of 
 1682 to be impeded or accelerated in its courfe, 
 by its approximation to Jupiter, went to work in 
 order to difcover by calculation, its approaches, 
 not only to Jupirer, but to the reft of the planets, 
 and to find out their attractive powers over it. 
 "What a ftupendous undertaking ! but let him 
 fpeak for himfelf. < The return of the comet of 
 
 * 1682, in the time prefcribed by the Newtonian 
 c theory, (advertifement to his theory of comets, 
 
 * Par. 1 7 60) is one of thofe events which diffufe 
 ' new light upon the laws of nature, and which 
 *■ conftitute a memorable aera in fcience. An e- 
 
 * vent which has effectually duTipated the laft: re- 
 
 * maining cloud which could poflibly obfcure the 
 i fyftem of attraction.' 
 
 " In the year 1 757, I had a mind to make a 
 new application of the folution I had given of a 
 famous problem ten years before *, to demonftrate 
 the univerfality of gravitation. The fubject which 
 afforded me this new application, was the comet 
 
 * This was the problem of three bodies, firft applied to 
 the theory of the Moon. Vide Principia, lib. iii. prop. 15. 
 prob. 6.' 
 
OFGOMETS. 59 
 
 of 1682, which was then expected to return ac- 
 cording to Halley's prediction from Newton's the- 
 ory. As the action of the great planets upon this 
 comet might produce one or many years variation 
 in its period, it rendered its return fo uncertain 
 that it was equally expected in 1757 or 1 759*. 
 
 * Though this has been afferted by Mr. Barker and many 
 others, from the firfl edition of the Synopfis of comets pub- 
 Jifhed in 1705 ; yet it is not exact. Dr. Halley then indeed 
 foretels the return of this comet in 1758. But many years af- 
 terwards, when he had carefully fearched into the catalogues 
 of ancient comets, and difcovercd that three others in the fame 
 order, and at like intervals of time, had preceded the three 
 upon which his conjecture was founded, he began to be much 
 more confirmed in his former opinion, of all thefe being one 
 and the fame comet. But, after accounting for fome fmall 
 diverfity in their inclinations and periods- from the action of 
 Jupiter, which, by its attraction, alters the proper velocity 
 of the comet when in its neighbourhood, the doctor adds, 
 ' it is probable that its return will not be till after the period 
 
 * of fcventy-fix years or more, about the end of the year 1758* 
 ' or the beginning of the next. Circa finem anni 1758, velini- 
 ' tium proximi futurum.* This puts the year 1757 quite out 
 Of the queftion 
 
 N. B. The above is taken from Dr. Halley's Tabulae A- 
 ftronomicae, publiibed in 1749, feven years after the author's 
 death, and ten years before the accompliihmenc of his pre- 
 diction which he finifhes by thefe remarkable words. * You 
 
 * fee therefore an agreement in all the elements of the three 
 
 * lafl appearances, (in 1531, 1607, and 1 68 x) which would be 
 4 next to a miracle if they were three different comets, or if it 
 
 * was not the approach of the fame comet towards the Sun 
 
 * and earth, in three different revolutions round them, Where- 
 
 * fore, if according to what we have already faid, it fhould 
 
 * return again abont the year 1758, candid poflerity will not 
 « refufe to acknowlege that this was firft difcovered by an En- 
 
 * glifhman.' 
 
6o THE HISTORY 
 
 I propofed therefore to find the true time when 
 the expected comet would feach its perihelion." 
 
 H The labour upon which I entered was im- 
 menfe, and I was unable to arrive at any certain 
 conclufion before the Autumn oi 1758. 1 then 
 thought it behoved me not to lofe a moment, ere 
 I acquainted the public and aftronomers, with the 
 refult of my operations." 
 
 November 1 4, 1 75S, he prefented to the Royal 
 Academy of Sciences a memorial upon the fubjefr 
 and fuccefs of his enquiries. He there undertakes 
 to prove, that the retardation of the expected co- 
 met, fo far from injuring, would confirm the fy- 
 ftem of attraction, as it was a necefTary confequence 
 of the extent of that power. * This is a quefti. 
 f on which has not hitherto been examined by 
 
 * geometricians: if it had, the refult muft always 
 
 * have been given conditionally. A body which 
 1 pafTes into fuch remote regions, and remains out 
 ' of fight during fuch long intervals, may be af- 
 1 fecled by caufes wholly unknown to us; fuch 
 « as the action of other comets, or even by planets, 
 ' too diftant from the Sun ever to be perceived 
 < by us." 
 
 After this author had calculated all the diftur- 
 bance that Jupiter might have occafioned to the 
 comet during its three entire revolutions, a new 
 difficulty occurred : he found it necefTary to go 
 
OF COMETS, 6t 
 
 through the fame operations with regard to Saturn ; 
 the mafs of which planet being one third of that 
 of Jupiter, might, cceteris paribus, produce one 
 third of its effect : and that was fufficient to merit 
 a particular examination. 
 
 As to the other heavenly bodies in our fyftem, 
 their mafTes not amounting to the hundredth part 
 of thofe of the two fuperior planets, their effect 
 is almoft infenfible. — He found that the action of 
 Jupiter upon the comet, during the whole revolu- 
 tion of 1 53 1 to 1607, had occafioned a diminu- 
 tion of nineteen days in its period, which would 
 not have happened by the mere force of the fun ; 
 and at the fame time had altered its elements fo as 
 to produce an acceleration of near thirty one days 
 in the following period. 
 
 " Proceding afterwards to the Revolution from 
 1607 to 1682 : The action of Jupiter turns out 
 much more confiderable ; for it occafions an ac- 
 celeration of about 420 days, which added to the 
 31 refulting from the action of the fame planet 
 during the preceding period, amounts in all to 
 45 1 days of diminution in the time of its period ; 
 which would not have happened merely by its in- 
 clination to the fun." 
 
 " Now if we take the difference of thofe two 
 accelerations, in order to know how much Short- 
 er the fecond period was than the firfl, it appears 
 F 
 
62 THE HISTORY 
 
 to be 432 days ; which differs only 37 days from 
 the time refulting from the obfervations." 
 
 " And this period appears to be ft ill diminifhed 
 by the action of Saturn. Indeed this diminution 
 is not much, becaufe the effects of Saturn's force 
 are almoft reciprocally deltroyed in the two firft 
 periods." 
 
 " Hence we fee that the theory gives within a 
 month, the difference fo remarkable between the 
 two known revolutions of this comet. Now if 
 we confider the length of thefe periods, the com- 
 plication of the two caufes of their irregularity, 
 and the nature of the problem by which they are 
 meafured ; this new demonftration of the Newto- 
 nian fyftem will perhaps be found as ftriking as 
 any one that has hitherto been given." 
 
 " By comparing, in like manner, the force of 
 the action of Jupiter, during the fecond period of 
 the comet, with that . which will be terminated 
 at its approaching return ; I find the revolution 
 about which we are at prefent interefted will be 
 518 days longer than the preceding, occafioned 
 by the action of Jupiter upon the comet, from its 
 laft mean diftance to its perihelion : that is, for 
 the laft feven or eight years ; an interval, during 
 which there can hardly be more than fifteen days 
 alteration." 
 
 " As to Saturn, the refult of its action on the 
 
OF COMETS, 63 
 
 comet is much more confiderable, compared with 
 the two firlt revolutions ; for I find the prefent 
 period protracted more than 100 days by it, in- 
 dependent likewife of its action fince 1 751, and 
 another fmall object which I have not had time 
 to determine. From thefe confiderations, then, it 
 appears to me that the expected comet ought to 
 arrive 1 at its perihelion, about the middle of the 
 month of April next enfuing." 
 
 This is a long quotation, but the fubject of the 
 memoir is curious, and the fuccefs of M. Clair- 
 aut, in determining fo nearly a point of fuch im- 
 po'rtance to anronOmy, and fo interefting to all 
 lovers of fcience, makes us as defirous to render 
 it public, as to augment that fame to which he 
 has fo juft a title. 
 
 But M. Meflier, in an admirable memoir pre- 
 fented to our Royal Society in 1765, (of which 
 an excellent tranflation by D. Matty is published 
 in the tranfactions of that year,) has done juftice 
 to Mr. Clairaut. And as this memoir, confuting 
 of thirty pages, contains a minute and fatisfactory 
 detail of the manner, in which the famous comet 
 in queftion was firft difcovered at Paris, by M. 
 Meffier, and afterwards obferved by him and M. 
 de L'ille ; we mall make no apology to our rea- 
 ders for giving them a long extract: from a perfor- 
 F 2 
 
64 THE HISTORY 
 
 mance fo fraught with entertainment and induc- 
 tion. 
 
 1759. - ^ n tne predictions of the heavenly 
 phenomena, which depend on the motion of the 
 ftars, two things are to be confidered ; viz. the 
 time and place. As to the time, when the velo- 
 city, and direction of the ftars in their motions, 
 both apparent and real, are known ; the time of 
 their different appulfes and afpecls may always be 
 foretold ; and the accuracy of the calculations de- 
 pends on the exactnefs with which their velocity 
 and their feveral inequalities are afcertained. Now 
 it is well known, that all the former uncertainty, 
 as to the exact time of the return of the comet 
 foretold by Dr. Halley, was owing to the variati- 
 <. is it muft have undergone from its feveral fixati- 
 ons, and approximations, to the planets, in its 
 progrefs thro' the folar fyftem." 
 
 " Dr. Halley, who was firft aware of the un- 
 equal returns of this comet in its former appear- 
 ances, which he found to have been alternately of 
 75 and 7 6 years, waslikewife the firft who aflign- 
 ed their true caufe. He afcribed it, as I faid a- 
 bove, to the nearer, or more diftant approaches 
 of the planets of our fyftem : and having obferved, 
 that the comet we are fpeaking of, came very near 
 Jupiter in the fummer of 1 68 1, above a year be- 
 fore its laft appearance, and remained feveral months 
 
OF COMETS. 6s 
 
 in the neighbourhood of that planet, he judged 
 that circumftance alone fufficient to have confide- 
 rably retarded its motion, and prolonged the du- 
 ration, of its revolution. Hence he concluded, 
 that its return was not to be expected till the latter 
 end of i 758, or the beginning of the next year." 
 " Dr. Halley obferves, in confirmation -of this 
 opinion, that the action of Jupiter upon Saturn, 
 is alone fufficient to alter the duration of Saturn's 
 period one whole month ; and he adds, how 
 much greater irregularities mud not a comet be 
 liable to, which, at its remoteft difhnce, gets near 
 four times farther from the Sun than Saturn ; and 
 whofe velocity, in drawing near the Sun, needs 
 but a very fmall increafe to change its elliptic into 
 a parabolic curve." 
 
 " Dr. Halley does not determine more exactly 
 the time of the return of the comet of 1682; 
 neither could he do it, but by determining exactly 
 the effect of the neighbourhood of Jupiter; which 
 muft very fenfibly affect the velocity with which 
 the comet was moving towards the fun. Befides, 
 regard muft be had, not only to this approach to 
 Jupiter in 1 6$ 1 , butlikewife to the other approach- 
 es to this, and all the other planets, which act: 
 more or lefs upon the comer, as they do upon 
 each other. In fhort, it was necefTary to confider 
 all the diiFererit fituations and diftances of all the 
 F 3 
 
66 THE HISTORY 
 
 planets, with regard to the comet, during the whole 
 of its laft revolution ; and even during the former 
 ones, when the returns had been found to be un- 
 equal." 
 
 M What immenfe labour ! and what geome- 
 trical knowlege did this talk not require ? M. 
 Clairaut, of the Royal Academy of Sciences, under- 
 took it ; and his refults differed but one month 
 from the obfervation. No fmall degree of exact - 
 nefs this, confidering the immenfity of the object. 
 In November 1758, he publimed his conclufion, 
 which allowed about 618 days more for the 
 period that was to end in 1759, than for the 
 former; whence he inferred, that the comet mud 
 be in its perihelion, towards the middle of April. 
 He added however, (Journal des Scavans, Jan. 
 1 759) ■ Any one may think with what caution I 
 venture upon this publication, fince fo many fmall 
 quantities, unavoidably neglected by the methods 
 of approximation, may very poffibly make a 
 month's difference, as in the calculation of former 
 periods/ It accordingly proved fo, the comet 
 having reached its perihelion on the 1 3th of March 
 in the morning. M. Clairaut has fince publifhed 
 the methods and calculations, by which he has ar- 
 rived at this conclufion." 
 f* The impatience of afixonomers, and their defire 
 to prepare for verifying this prediction of Dr. Hal- 
 
O F C O M E T S. 67 
 
 ley, had put them upon enquiring for feveral years, 
 in what part of the heavens this comet was likely 
 to appear ; but being ignorant of the exact time 
 of its return, they could not determine the fpot 
 where it might be expected to be feen, but by 
 making various fuppofitions as to the time of its 
 perihelion. This Mr. Dirck of Klinkenberg, a 
 famous allronomer in Holland, had attempted fe- 
 ven or eight years before ; having taken the pains 
 to calculate the principal points of fourteen differ- 
 ent tracts, which the faid comet was to take, up- 
 on as many different fuppofitions relating to its paf- 
 fage thro' its perihelium, almoft from month to 
 month, from the 19 th of June 1 757, to the 15th 
 of May 1758. Meflrs. Pingre, and de la Lande, 
 proceeded much in the fame manner in the calcu- 
 lations they publifhed in the memoirs of Trevoux, 
 for April 1759, firft and fecond parts ; with this 
 difference, that the latter in their fuppofitions had 
 taken narrower limits, and nearer to M. Clairaut's 
 determination, who, as I faid before, had fixed the 
 return of this comet to the middle of April." 
 
 " M. de Lifle, being curious of feeing the co. 
 met on its firfl return, as foon as it could be dif- 
 covered by means of refracting, or reflecting te- 
 lefcopes, before it was vifible to the naked eye, 
 thought he mull proceed in a different manner 
 from what other aftronomers had done, to find 
 
OS THEJIISTORY 
 
 out in what part of the heavens it mud be looked 
 for. He confidered, that it was not neceflary to 
 know its place throughout its whole courfe, but 
 only at the firft moment of its appearance ; be- 
 caufe, having once found it out, it would be an 
 eafy matter afterwards to trace it thro' its whole 
 progrefs by obfervation and calculation." 
 
 " A full defcription of this method is to be 
 found in an ample memoir concerning this comet, 
 which I have laid before the Royal Academy of 
 Sciences, at Paris ; and which no doubt will be 
 printed in their collection, together with a northern 
 hemifphere, by means of which I have been ena- 
 bled to look for this comet, in the very place of 
 the fky, where it ought to appear : and it was 
 by the help of this planifphere, that I actually. dis- 
 covered the comet from the Marine Obfervatory at 
 Paris, on the 21ft of January in the evening, af- 
 ter fearching for it two years fuccelTwely, whenever 
 the iky would permit. The weather was extremely 
 clear the 2 1ft of January the whole day and even- 
 ing. I feized this opportunity, and as foon as the 
 flars were vifible after fun-fet, I examined through 
 a Newtonian telefcope of four feet and an half, 
 thofe places of the fky, where the planifphere Shew- 
 ed that the comet was to be expected." 
 
 " After much pains, I perceived about feven 
 o'clock, a light refembling that of the comet I had 
 
O F C O M E T S. 6g 
 
 obferved the year before in Auguft, September, 
 October, and the beginning of November *. I 
 immediately made a configuration of this new 
 light, with refpeft to the neighbouring ftars, in 
 order to examine the next night, whether it had 
 any motion among the fixed ftars. This light ap- 
 peared pretty large, and in the middle I obferved a 
 nucleus, or bright fpot, which was no proof as yet 
 that it was a comet, as there are fome nebulous 
 ftars with a bright fpot in the middle." 
 
 " January 22, at the fame hour as the day be- 
 fore, the fky being equally clear, I again faw the 
 fame light with a four feet and an half telefcope, 
 and found it had fenfibly changed its place ; but 
 its appearances were the fame. From this fecond 
 obfervation I no longer doubted of its being a co- 
 met." 
 
 According to M. Meilier, this comet had three 
 feveral appearances above the horizon, which M. 
 de Lifle, and he calculated, as foon as they had 
 made their firfl obfervations, that is, as early as ther 
 month of February. 
 
 " The firft appearance of this comet was in the 
 evening, from January the 2 r to February 1 4, 
 when I ceafed feeing it, by reafon of its entrance 
 into the rays of the Sun. The fecond appear- 
 
 * See Mem. del'Acad. Roy. des Scienc. Anno 175$, 
 
7» THE HISTORY 
 
 ance was at the comet's getting clear of the rays 
 of the fun, in the morning, after the conjunction 
 with that luminary, which was to take place a few 
 days before its paflage through the perihelion. I 
 obferved it in the morning from the i ft of April 
 to the i 7 th, when it entered the rays of the fun 
 a fecond time." During this fecond appearance, 
 the comet was much larger, and brighter than in 
 the middle of February j and indeed it was but i 8 
 days part its perihelion. Now it is well known 
 that comets are much brighter after their perihelion, 
 than at the fame diftance before it. fi Befides (fays 
 M. MefSer) the comet after palling the perihelion, 
 was as near again to the earth as on the 1 4th of 
 February, when I loft fight of it at night. When 
 I faw this comet again on the 1 ft of April, I 
 could very plainly difcern its tail, but could not af- 
 certain its length, becaufe of the morning twilight, 
 which was then beginning, and foon encreafed 
 much : it filled the field of the telefcope ; and 
 uiuft have extended far beyond : according to 
 what I have obferved, the tail of the comet muft 
 have fpread to more than 25 degrees; the nu- 
 cleus was considerable, but not well terminated, 
 and it apparently exceeded the fize of ftars of 
 the firft magnitude ; it was of a pale whitifh 
 colour, not unlike that of Venus. The nebu'o- 
 
OF COMETS, 71 
 
 fity which (unrounded the nucleus, and went on 
 leffening, (hewed reddifh colours ; and thefe co- 
 lours grew more vivid, towards the brighteft part 
 of the tail. The morning twilight, which in- 
 creafed apace, foon put an end to thefe appear- 
 ances, and afterwards made the comet itfelf difap- 
 pear ; however, I had been able to perceive it with 
 the naked eye, when it was fomewhat difengaged 
 from the vapours of the horizon." 
 
 «• The third appearance of the comet was on 
 the 29th of April in the evening, and I went on 
 obferving it till the 3d of June at night, when I 
 faw it no more." During this laft apparition, May 
 1, it appeared to the naked eye larger than liars of 
 the firft magnitude, the nucleus furrounded with 
 a great coma. Its light was but faint, like that 
 of the planets feen through the thick vapours of 
 the horizon. It would have appeared brighter but 
 for the light of the moon. In this laft appearance 
 of the comet above the horizon, it was in the fex- 
 tant, and was obferved by moil of the afrronomers 
 in Europe, The whole duration of its appearance 
 was 1 34 days, reckoning from the 2 ill of Janu- 
 ary to June 3. 
 
 M- de la Lande's account of the return of this 
 comet, (prefixed to his edition of Dr. Halley's a- 
 ftronomical tables, publifhed in 1 759, juft after 
 the departure of the comet) is very full, and fa- 
 
72 THE HISTORY 
 
 tisfa£rory. We fhall therefore prefent our rea. 
 ders with fuch paffages of that work as feem moil 
 interefting, flrft premifing, that M. Clairaut con. 
 fefTes himfelf obliged to M. de la Lande for affix- 
 ing him in his great work of calculating the diftur- 
 bances incident to the comet from its vicinity to 
 Jupiter, &c. And M. de la Lande again, on his 
 part, feems willing to participate this glory with 
 Madam Lepaut, a lady who has long and fuccefs- 
 fully been employed in agronomical calculations, 
 to whom he acknowleged himfelf indebted for help 
 in the part he had undertaken. 
 
 " The whole univerfe, fays this author, has 
 been witnefs to the accomplifnment of Dr. Halley's 
 famous prediction, by the return of the comet of 
 i 682, which defcended to its perihelion May 1 3, 
 17 59 y a ^ ter a period of 27937 days, or 76 years 
 and 6 months." 
 
 «* A German pamphlet publifhed at Leipfic laft 
 January, and many printed letters from Germany 
 allure us, that it was feen by a peafant in the neigh- 
 bourhood of Dxefden, fo foon as the 25th of De- 
 cember 1758. An aftronomer of the fame coun- 
 try alfo obferved it foon after, of which he gave 
 information to feveral of his friends *. And M. 
 
 * M. leMonnier (Mercurede France, Apr. i759«) remarks, 
 that not only this comet had been firft feen in Saxony, but the 
 great one of 1680 had been feen there likewife two months 
 
OF COMETS. 72, 
 
 MeiTier difcovered it at M. de Lifle's, 2 i ft of Ja- 
 nuary (as related above.)" 
 
 " The public was much furprifed at this comet 
 having no tail vifible to the naked eye, though it 
 always had one in its former appearances. Eu- for 
 this many reafons may be afligned. In the month 
 of Apiil, indeed, though the comet was near the 
 Sun, yet it was very far from the earth — from 
 whence it could only be feen during the twilight. 
 Now, it is well known, that not only the twilight, 
 but even the light of the moon is fufficient to ef- 
 face the tail of a comet. Hence we mould ceafe 
 to wonder that no tail appeared in the month cf 
 April — let us fee now what was its pofition in 
 1607 and in 1682, when the fame comet is 
 faid to have appeared with a remarkable tail. Sep- 
 tember 20th 1 607, Longomontanus faw it with 
 a very long and denfe tail, which was 2 8 days be- 
 fore its perihelion ; now fuppc t the earth's di- 
 fiance from the fun to be as 10, the comet was 
 
 before it was obferved either in France or England. Occafi- 
 oned, according to this eminent aftronomer, by the land to 
 the eaftward of that electorate being Tandy and dry. And as 
 the eaft winds bring few clouds, they have there caim wea- 
 ther and a clear fky. " It is to be wiflied, fays M. le Mon- 
 " nier, that thofe who inhabit climates where the fky is more 
 " ferene than ours, may have watched this comet as narrow- 
 * { ly as has hitherto been done in France ; to fuch it will 
 " be vifible in the fextant, that is to fay, a little below Leo, 
 " till the end of July." 
 
 G 
 
74 THE HISTORY 
 
 then only 2 of thofe parts diftant from the earth, 
 and 8a from the fun. Auguft 29, 1 682, M. 
 Picard faw the comet with a tail 30 degrees long ; 
 Hevelius allowed it only 1 6 degrees : but this was 
 1 6 days before its perihelion ; it was then diftant 
 from us 34. iothi and from the fun 64.." 
 
 " Hence in both cafes, there is a more favour- 
 able combination in its difrance, both from the 
 fun and the earth, than when it laft appeared, 
 which is fufficient to explain the different figure it 
 made. We mould then treat with all due contempt 
 every fufpicion of this comet not being the fame 
 as that of 1 682 : its inclination, perihelion, nodes, 
 diftance from the fun, motion *, and even its late 
 arrival occafioned by the attractions of Jupiter and 
 Saturn, which fo well agree with calculation ; all 
 thefe circumftances amount to fo full and ftriking 
 a demonftration, 'hat I am afhamed to ftop a 
 moment at fu * difficulties. However, as the a- 
 cademy always publishes the refult of its labours j 
 and as doubts, however groundlcfs, always occa. 
 lion a fufpenfion in the progrefs of the human 
 mind, I thought I mould be excufed by men of 
 fcience if I tried to remove objections which, per- 
 
 * All thefe may be feen and compared by anyone who will 
 take the trouble to inform himfelf of the meaning of thefe 
 terms, and to caft his eye over the following table, conftruct- 
 cd by the Abbe de la CaiJle. Lecons d'Aftronomie i7<Ji. 
 
^ ft CMfl^i 
 •*> 00 O w i*\ 
 O H ^1 „ ft 
 
 Year 
 
 of 
 
 Appearance. 
 
 
 >J K> N - w 
 
 W O OO 00 
 
 « 00H (a o 
 O O O o 
 
 bo 
 
 IS, 
 
 o — 
 D p 
 
 B>.fl 
 
 
 O o o 
 
 in 
 
 o ►«, 
 
 ft D 
 
 5* 5* 
 
 
 O O o 
 t* CV C\V0 
 
 o o o o o 
 
 yi 
 
 :T ft 
 ft. ft 
 
 3 
 
 
 \0 <C VO »C <0 
 >J ~4 «j ^4 -a 
 
 6>\m OC w si 
 O H 4* <** \* 
 U> no O 00 4» 
 
 ^o c\ o ^ o 
 
 Log. of die 
 Perihelion 
 Di fiance. 
 
 
 & 3 §• 5, ° 
 
 - ? a ^ 
 
 - M H ^ 
 
 ** -^ o> 4* oo 
 
 * W Vl ^ H 
 
 - - V3 -v, o 
 
 P 
 a 
 % 
 
 p~' 
 
 ft ,- 
 
 B 5" 
 
 jr. c 
 3 £ 
 
 5 5- 
 5* 2. 
 
 
 Retrograde 
 
 Retr. 
 
 Retr. 
 
 Retr. 
 
 Retr. 
 
 i 
 
 o 
 
 o' 
 a 
 
 
 Pringre. 
 Halley. 
 Halley. 
 Halley. 
 La Caille. 
 
 Orbit by 
 
 whom 
 
 Calculated 
 
 
 
 
 
 
 w 
 
 w 
 w 
 
 co 
 O 
 
 rt> 
 
 < 
 ft) 
 
 p 
 
 o 
 o 
 
 a 
 
 > 
 
 r 
 
 w 
 
 k! 
 
 CO* 
 
 o 
 
 O 
 
 B 
 
 w 
 
 w 
 
 o 
 
 o 
 
 w 
 
 H 
 
 
76 THE HISTORY 
 
 haps, with fome may gain credit, however ill 
 founded." 
 
 The rnoft important objection, as to the return 
 of this comet, arifes from the inequality of its 
 periods, which were as follows : that from Auguft 
 2 5> I 53 I > to the 2 6th of October 1607, was 
 performed in 76 years, and two months ; that 
 from October 2 6, 1 607, to September 14, 1 682, 
 was rather lefs than 75 years; and its laft period 
 from the 1 4th of September 1 682, to the 3th of 
 March 1759, which was the longeft of all, was 
 76 years and fix months; or 27,937 days, a- 
 mounting to 58 3 days more than in the preceding 
 period. 
 
 Dr. Halley was aware of thefe differences, and 
 at firfl confefled himfelf to be a little daggered by 
 them, nor would he have had the courage to pro- 
 nounce its return fo pofitively, if hiftory had not 
 informed him, that comets had appeared in 1 456, 
 1380 and 1 305, which put their identity out of 
 all doubt. 
 
 Thefe appearances happening alternately in fe- 
 venty-five and feventy-fix years, and as the preced- 
 ing period was only of feventy-five years, it was 
 natural to fuppofe that the next would amount to 
 feventy fix. But as the difficulties arifing from thefe 
 inequalities in the periods have been forefeen and 
 
OF COMETS. 77 
 
 obviated by Dr. Halley, we cannot do better than 
 to infert his own words. 
 
 " Perhaps fome may object to the diverfity of 
 their inclinations and periods, which is greater 
 than what is obferved in the revolutions of the 
 fame planet ; feeing one period exceeded the o- 
 ther by more than the fpace of one year, and the 
 inclination of the comet of the year 1682, ex- 
 ceeded that of the year 1 6o 7, by twenty-two en- 
 tire minutes. But let it be confidered what I 
 mentioned at the end of the tables of Saturn, where 
 it was proved that one period of that planet is 
 fometimes longer than another by thirteen days ; 
 and that is evidently occafioned by the force of 
 gravity tending towards the centre of Jupiter, 
 which force indeed in equal diftances is only the 
 thoufandth part of that force tending to the Sun it- 
 felf, by which the planets are retained in their or- 
 bits. But by a more accurate computation, the 
 force of Jupiter towards Saturn, for example, in 
 the great conjunction as they call it, January 26, 
 in the year 1 68 3, was found to be to the force 
 of the Sun upon the fame Saturn, as 1 to 186; 
 the fum of the forces therefore is to the force of 
 the Sun, as 187 to 186. But at the fame dif- 
 tance from the center, the periodic times of bodies 
 revolving in a circle are in the fubduplicate ratio 
 of the forces with which they are urged : where* 
 G 3 
 
7$ THE HISTORY 
 
 fore the gravity being increafed by i 8 6th part of 
 itfelf, the periodic time will be fhortened by about 
 the 374th part, that is, by a whole month in Sa- 
 turn. How much more is a comet liable to thefe 
 errors, which makes its excurflon near four times 
 higher than Saturn : and whofe velocity being in- 
 creafed by lefs than the 120th part of itfelf, 
 would change its elliptic orbit into a parabolic tra- 
 jectory." 
 
 " But it happened in the fummer of 1681, 
 that the comet feen in the following year, in its 
 defcent towards the Sun, was in conjunction with 
 Jupiter in fuch a manner, and for feveral months 
 fo near him, that during all that time it mull: have 
 been urged likewife towards the centre of Jupiter 
 with near the 50 th part of that force by which it 
 tended towards the Sun : whence, according to 
 the theory of gravity, the arc of the elliptic orbit, 
 which it would have defcribed had Jupiter been ab- 
 fent, muft be bent inwards towards Jupiter in an 
 hyperbolic form winding, and have affumed a 
 kind of curve very compounded, and as hitherto 
 not to be managed by the geometers ; in which 
 the velocity and direction of the moving body, in 
 proportion to the caufe, would be very different 
 from what it otherwife had been in the ellipfes. ,> 
 
 " Hence a reafon may be affigned for the change 
 of its inclination : for as the comet in this part of its 
 
OF COMETS. 79 
 
 path had Jupiter on the north almoft in a perpen. 
 dicular dire&ion to its path, that portion of its or- 
 bit mud be bent towards that quarter ; and there- 
 fore its tangent being inclined to a greater angle 
 towards the plane of the ecliptic, the angle of the 
 inclination of the plane itfelf muft be neceflarily 
 increafed. Bcfides the comet continuing long in 
 the neighbourhood of Jupiter, after it had come 
 towards him from parts much more remote from 
 the Sun with a flower motion, and now being 
 urged with the joint central forces of both, muft 
 have acquired more accelerated velocity, than it 
 could lofe in its recefs from Jupiter, by forces 
 adting a contrary way, its motion being more 
 fwift, and the time being lefs." (Tabulce Aftrono* 
 micx) 
 
 When the comet of 1682 defcended towards 
 the Sun and became viilble, Europe had fcarce 
 recovered from the terrible panic into which it 
 had been thrown but eighteen months before by 
 the great comet. However, this was comparative- 
 ly too inconfiderable to be much regarded, for it 
 was little imagined then, that the leaft of the two 
 would become the moft interefting, and that it 
 would be for ever celebrated by pofterity for hav- 
 ing taught mankind how to know all the reft. But 
 however inferior to the other this comet may have 
 appeared in vulgar eyes, aftronomers obferved it 
 
80 THE HISTORY 
 
 with the greateft attention. Hevelius at Dantzick, 
 Kirch at Leipfic, Flamftead and Halley in England, 
 Zimmerman at Nurenburg, Baert at Toulen, Mon- 
 tanori at Padua, and Picard, CafTmi and la Hire 
 at Paris. This lift of names will fufrice to lhew 
 that there can be no fcarcity of good obfervations 
 upon this comet during that appearance. 
 
 In i 607 it was obferved by the famous Kepler, 
 who publifhed his obfervations together with his 
 general theory (de Cometis Libelli 3, autore Jo- 
 anne Keplero, augufta? vindelicorum 161 9.) The 
 1 6th of September old ftile, the fky being very 
 clear, Kepler firft faw this comet upon the bridge 
 at Prague, and though it had no tail when he 
 firft difcovered it, yet afterwards it had one of a 
 confiderable length and fplendor. It was likewife 
 obferved by Longomontanus, September 1 8, (A- 
 fir on. Daniae appendix, Amft. 1 640.J he fays it 
 appeared as large as Jupiter, though with a very 
 obfcure and pale light ; that the tail was pretty 
 long and more denfe than the tails of comets u- 
 fually are, but as pale in colour as the comet itfelf. 
 
 In the preceding revolution of 1531* we find 
 our comet obferved by the aftronomer Appian at 
 Ingoldftadt, the fame who firft remarked that the 
 tails of comets were always in an oppofite directi- 
 on to the Sun : which to him was an evident proof 
 that the Sun was the caufe of fuch eruptions. 
 
OF COMETS, 81 
 
 In 1456, there was a very remarkable exhi- 
 bition of the fame comet. Cometa in audita? mag- 
 nil l u dints toto menfe Junii cum pra?longa Cauda, it a 
 ut duo ferefigna coeli comprehenderit. (Theatrum 
 Comet ;) 
 
 It is difficult to comprehend how the comet 
 whofe tail was fo inconfiderable in its laft appear- 
 ance, fhould in this have one of fixty degrees : but 
 M. de la Lande in his theory of comets, p. 127. 
 accounts for this difference in the following man- 
 ner. " I find, fays this acYrve aftronomer, that 
 if the comet reached its perihelion in the beginning 
 of June, it ought to have appeared at night to- 
 wards the middle of the month with fixty degrees 
 of elongation and a very northern latitude, its di- 
 ftance from the earth being lefs than the femidia- 
 meter of the Sun : fo that in this pofition, which 
 of all others is the mod favourable, it mult have 
 appeared in all the fplendor allowed to it by the 
 old chronicles. Perhaps by duo Jigna, they only 
 mean the extent of two conftellations, which is 
 often much lefs than two figns of the ecliptic." 
 
 In 1 379 and 1 380 we fled two comets men- 
 tioned by Alftedius and Lubienietzki, but without 
 any particulars as to the time or form of their ap- 
 pearance. 
 
 In 1305, our comet again appears, according 
 to the hiftorians of that time, in all its terrors. 
 
82 THE HISTORY 
 
 Cometa horrendce magnitudinis vifus eft circa fe* 
 rias pafchatis, quern fecuta eft peftilentia maxima ; 
 it is very likely that the horror occafioned by the 
 plague had augmented the terrible impreflion left 
 by the comet; however, upon calculation, it does 
 appear that the comet muft this year have pafled 
 very near the earth. 
 
 The hiftory of this comet might be traced much 
 higher by confuhing Eckftormius, Riccioli, Alfte- 
 dius, and Lubienietzki. Among the four hundred 
 and fifteen comets mentioned by this laft writer, 
 we find one for the year 1230, which appears to 
 be the very comet in queftion •, another in 1005, 
 three periods before; it is found in 930, and 
 higher up in the year 550, marked by the taking 
 of Rome by Totila. All the hiftorians of the em- 
 pire fpeakof a great comet in the year 399, which 
 may have been the fame; Cametafuit prodigiojce 
 magnitudink y horribitis afpsftu, comam ad ter- 
 rain ufque dimittere vi/us. 
 
 In 323, that is to fay, feventy-fix years before, 
 a comet alfo appeared in Virgo ; and in fhort it 
 would be eafy to mount, without quitting the 
 fame periods, as high as 1 30 years before Chrift, 
 when, according to Juftin. one appeared at the 
 birth of Mithridates. But, in thefe early periods, 
 there would be great dinger of meeting with fome 
 of thofe fabulous comets with which it was thought 
 
OF COMETS. 83 
 
 neceiTary perhaps to embellifh every famous reign: 
 and it muft be confeffed too, that equal intervals 
 between the different apparitions of comets, are 
 not alone fufricient to prove their identity : fuch 
 equalities may indeed contribute towards the fup- 
 portof a demonftration founded on an agreement 
 in their motions, and a perfect correfpondence in 
 the other circumfhnces of their appearance, but 
 greater ftrefs muft not be laid upon them : for 
 thefe compilations were not formed with the fame 
 care and exaclnefs, which would have been beftow- 
 ed upon them, if, when they were made, it had 
 been fufpected what advantages were to be derived 
 from them. Lubienietzki feems to have had no 
 other view than to compare the events fubfequent 
 to the appearance of comets, in order to prove 
 that they have prefaged nothing : juft as his pre- 
 deceflbrs, among whom was the good father Ric- 
 cioli, had compiled them in order to prove them 
 to be inaufpicious augurs, 
 
 Riccioli, in his Almageft. published in 1651, 
 enumerates 154 comets to be found upon record 
 in hiftory, the lafr. of which appeared in I 61 8. 
 But in the great work of Lubienietzki #, (a Poliih 
 gentleman defcended from the Sobiefki family, 
 but who being tainted by Socinianifm was forced 
 
 * Theatrum Comcticum, Amft. i<J<58. 
 
84 THE HISTORY 
 
 to quit his country,) where not a fingle hifiorical 
 circumftance relative to comets is omitted, the 
 number in 1 665 amounted to 415. " Since 
 that time, fays M. de la Lande, in 1 7 64 (Aftro- 
 nomie, 2 vols. 4to) they are increafed to 450. 
 But of all thefe appearances, no comet had its path 
 aftronomically defcribed till 1 2 64 *, and the num- 
 ber of thofe which have been obferved, with fuf- 
 ficient accuracy to determine their orbits, is reduc- 
 ed to fifty one, exclufive of the comet of 1 53 1 , 
 1 607, 1 682 and 1 759 which is allowed to be 
 only different returns of one and the fame co- 
 met." 
 
 It mould be remembered that though every me- 
 teor and (trange appearance in the heavens was by 
 the ancients called a comet, and that many of 
 thofe which were intitled to that appellation, were 
 the fame comers feen at different revolutions ; yet 
 it may eafily be fuppofed, that in every age, and 
 efpecially in the early ones, many comets have 
 appeared concerning which hiftorians have been 
 filent, as well as many others, which on account 
 of their diftance, or of cloudy ikies, have not been 
 vifible to the inhabitants of the globe. 
 
 We muft not wonder then, if among the 415 
 comets mentioned by Lubienietzki, there are near 
 
 * Tra&atus Fratris Egldii decometis. 
 
OF COMETS, 85 
 
 400 from which nothing pofitive can be conclude 
 ed. But whatever uncertainty there may be in 
 thefe remote periods, we have four returns of one 
 comet perfectly well afcertained, which joined to 
 that of 1 759, put the theory of this comet out 
 of the reach of cavil, and conftitute the greateft 
 triumph of aftronomy and the higheft glory of the 
 human mind. 
 
 Dr. Bevis obferved this comet in London, May 
 I and 2, and exultingly fays (Phil. Tranf. vol. 
 51 .) "I think 1 may now venture to pronounce 
 this to be the fame as the comet of 1682; and 
 am about making out its future track. If I pre- 
 fume rightly, it will in a fhort time become in a 
 manner ftationary, but diminifh very faft both in 
 fize and light, the earth and it, receding from each 
 other almoft in a right line. It is at this time 
 about four times nearer the earth than the Sun 
 is." 
 
 Mr. Muncley likewife obferved it at Hampftead, 
 April 30, May 1, 2, 5, and 6. « It is a lu« 
 
 * minous appearance, fays he, very evident to 
 
 * the naked eye (notwithstanding the light of the 
 « Moon, within two or three days of her qua- 
 c drature) yet rather dim than fplendid, large, but 
 
 * very ill defined, &c.' 
 
 We cannot quite this article without mention- 
 ing, that though the period of this comet is the 
 H 
 
86 THE HISTORY 
 
 fhorteft of any yet difcovered, (Dr. Halley calls 
 it the Mercury of comets) its aphelion, or greateft 
 diftance from the Sun, is thirty- five times greater 
 than that of the Earth, and four times greater 
 than that of Saturn, the moit remote of any of 
 the planets. 
 
 Indeed this comet, fo big with confequences, 
 feems, it mud be allowed, very diminitive as to 
 fize, compared with many others : however, no 
 one point in aftronomy ever engaged the attention 
 of fo many great aftronomers as the return of this 
 comet. Newton, Halley, Maupcrtuis, Clairaut, 
 de Lifle, le Monnier, la Caille, Meffier, la Lande, 
 Pingre, &c. have been indefatigable in obferving 
 and calculating its courfe. There was a contro- 
 verfy among the French aftronomers concerning 
 the methods of finding it, and the exact time of 
 its perihelion ; but they and all the aftronomers 
 in Europe were unanimous in pronouncing it to be 
 the fame comet which appeared in 1682 ; and 
 here we cannot help repeating, for the honour of 
 aftronomy and of the Englifti nation, that this co- 
 met was firft calculated, and its return predicted 
 by the great Dr. Halley, in confirmation of the 
 theory of the illuftrious Sir Ifaac Newton. 
 
 1 760. The comet of this year was difcover- 
 ed, in the confrellation Orion, at Cambridge, by 
 Dr. Mafon, and at Paris by M. Meffier, on the 
 
OFCOMETS. 87 
 
 fame night, and at the fame hour: namely, Janu- 
 ary 8, about nine o'clock in the evening. January 
 9, the late Mr. Short, Mr. Munckley of Lincoln's- 
 Inn, and Mr. Day at Lowick, Northamptonfhire, 
 feverally obferved it. They all fpeak of the ex- 
 treme rapidity of its motion, and of the body be- 
 ing ill defined ; but of the tail, thofe who faw it 
 in England, fay nothing, except Mr. Short, who, 
 after remarking that its motion was to the weft- 
 ward with a confiderable velocity, feemingly about 
 two degrees in a day, which was nearly at the 
 rate the great comet moved, when it was firft 
 feen in the end of the year 1743, ac ^ s > * This 
 < comet is very vifible to the naked eye, though 
 
 * I could perceive nothing of a tail, and therefore 
 
 * I conclude it is going down to the Sun.' But 
 the account of this comet in the Mercure de France, 
 of January 1760, fays, the tail has an eaftern 
 dire&ion, and is about four degrees long, but 
 fcarcely vifible 10 the naked eye. The late Dr. 
 Stukely feems to have thought this comet was the 
 fame as that of 1 664. But M. Barker (Phil. 
 Tran. vol. 52.) rather difcourages that opinion. 
 " The comet of 1 664, fays he, might have ap- 
 peared nearly in the fame place this was feen, with 
 a fwift motion of pretty many degrees in a day, 
 as a retrograde comet in oppofition to the Sun 
 generally hasj but, I think, would not have been 
 
 H 2 
 
S8 THE HISTORY 
 
 near enough to have moved a degree in an hour* 
 as this did ; and 1 think it would have been alfo 
 a larger, and continued longer than this ; for in 
 1664, it was feen four months, and when far 
 diftant from the earth ; and in the pofition it 
 mud have been in laft January, would hardly have 
 gone farther back than the beginning of Gemini, in 
 fmall north latitude, and is, I believe, one of the 
 largeft comets." 
 
 But M. Meffier, who firft difcovered in France 
 the three laft mentioned comets, feems to have 
 found this year a fourth comet, concerning which 
 he communicated his obfervations to the Royal A- 
 cademy of Sciences. This comet, wholly dif- 
 ferent from that of which we have been fpeaking 
 above, was firft feen by M. Meffier, January 2 6, 
 at which time it could be perceived only through 
 a foot reflecter, though foon after, with great 
 difficulty, by the naked eye. Its nucleus appear- 
 ed pretty clear, and well defined, through a 4 ■* 
 foot Newtonian telefcope. The day of its difco- 
 very, it was fituated between the conftellations 
 Crater and Hydra. February 4, it was vifible in 
 Leo : and on the eighth appeared to the naked eye 
 equal to a ftar of the third or fourth magnitude, and 
 was very brilliant, having a tail (vifible indeed only 
 through a telefcope) of many degrees in length, 
 -with a wetter n direction. 
 
OF COMETS. 89 
 
 ij6z. The comet which appeared this year, 
 is fuppofed by Mr, Struick and M. Pingre, who 
 both obferved it, and compared their obfervations 
 with thofe of other aftronomers, to be the fame 
 with that which appeared 1 69 years before, viz. 
 in 1 59 3. Its courfe was direct, and it arrived at 
 its perihelion, May 28. In conftructing the ele- 
 ments of this comet, a remarkable Angularity oc- 
 curred to M. Pingre : he found that it had pafled 
 eleven times nearer the Sun than the Earth does 
 when it is in its perihelion ; and likewife, that 
 though it was feen a very few days after its peri- 
 helion, and might be expected to have equalled 
 the celebrated comet of 1 680 in fplendor, yet it 
 did not exceed in brightnefs a frar of the third 
 magnitude, its tail at the fame time not extend- 
 ing above four degrees. M. Pingre therefore fup- 
 pofes it to have been very fmall, and that its at- 
 mofphere was not qualified to abforb or attract:, 
 according to M. Mairan's ingenious fyftem, a fuf- 
 ficient quantity of thofe luminous particles, which, 
 fays M. Mairan , eompofe the folar atmofphere*. 
 
 1764. Two comets are this year difcovered 
 by the vigilant and perificaciousM. Meffier. Thefe 
 fhrs by being fo numerous, will foon ceafe to be 
 
 * This article is extracted from the Hift. de l'Acad. des 
 Sciences, for the year 1763 , in which volume M. Bailly give* 
 feveral obfervations on the fame comet. 
 
 h 3 
 
90 THE HISTORY 
 
 regarded with the fame wonder as formerly ; how- 
 ever, it mud be owned, that the frequency of 
 thefe difcoveries is in a great meafure owing to 
 the ufe and improvement of telefcopes ; with- 
 out which, we mould know no more of many 
 that have lately been feen, than our fhort-fighted 
 forefathers did of the fatellites of Jupiter and Sa- 
 turn. As to M. Meflier, he is fo confhntly on 
 the look-out, and fo dexterous in difcovering 
 them, that it would incline one to believe with 
 Gaflini, that there was really a zodiac of comets, 
 and that M. Meflier alone knew its place and li- 
 mits in the heavens. 
 
 The firft comet of this year was difcovered at 
 the Marine Obfervatory at Paris, March the 8 th, 
 in the conftellation of Pifces, and obferved till the 
 1 5th of the fame month ; its motion was retro- 
 grade, and it feemed, in fize, equal to a ftar of the 
 fourth magnitude. 
 
 The fecond comet was at firft difcovered with 
 the naked eye, April the 8 th, near the Pleiades, 
 and promifed to become confiderable. The next 
 day the tail was fix or feven degrees long, and the 
 nucleus equally luminous with ftars of the third 
 magnitude. It was however vifible only till the 
 1 2 th. M. Meflier fent tables of the places of theft 
 comets to the Royal Society this year, together 
 
OF COMETS. 91 
 
 with a calculation of the elements of their orbits 
 by M Pingre. 
 
 The fecond of thofe two comets was difcovered 
 at Louifburg, in the ifland of Cape Breton, April 
 the 7 th, which was one day fooner than even M. 
 Meflier had feen it at Paris. In this observation, 
 made by Captain Holland, the tail of the comet ap- 
 peared perpendicular to the horizon, with its head 
 towards the fun. 
 
 Mr. Brice obferved the fame comet at Kirknew- 
 ton, April the 10 th. It was then defcending to- 
 wards the fun, at the rate of about fix degrees in 
 the fpace of twenty-four hours. To this gentle- 
 man's accounr, in the Philofophical Tran factions, 
 is prefixed a plate of the appearance of the comet. 
 
 1 767. The firit intelligence we had of this co- 
 met in England, was from the indefatigable M. 
 Meflier, aftronomer, keeper of the journals, plans 
 and maps belonging to the marine of France, who 
 difcovered it the 8 th of Auguft, about 1 1 in the 
 evening, in the conftellation Aries, between the 
 24th, 25th and 31ft liars of that conftellation in 
 the Britifh catalogue. On the 1 4th and 1 5th of 
 the fame month it appeared very diftinclly, hav- 
 ing a tail about fix degrees in length, This infor- 
 mation was inferted in the St. James's Chronicle, 
 Auguft 2 5, which fet us all to work in order to 
 find it here. Not many days had elapfed, ere it 
 
92 THE HISTORY 
 
 was feen by all who were poilefled of telefcopes, 
 and in the beginning of September, it was vifible 
 to the naked eye, about three o'clock in the morn- 
 ing, in the conftellation of Taurus, with a tail 
 fifteen degrees long. The body of this comet be- 
 came more confiderable to our view, till the mid- 
 dle of September, when the tail was of an enor- 
 mous breadth, and extended to upwards of 40 
 degrees in length. 
 
 The public is, doubtlefs, much obliged to Mr. 
 Dunn, for his obfervations, which appeared fo fre- 
 quently in the news papers, though he put them 
 in a great fright for our beautiful morning and 
 evening ftar, the planet Venus, which, " he 
 " thought likely to receive a bru/h from the co- 
 " met's tail." However, he did not furTer their 
 anxiety to continue long, but ventured two or 
 three days after to pronounce Venus out of dan- 
 ger. — But may we not fuppofe that the whole fo- 
 lar fyftem, that is to fay, our fun—with its fix 
 planets, ten moons, and comets, as yet unnumber- 
 ed, are fo combined together, fo dependent one 
 on another, and fo much one family, that nei- 
 ther Venus, the Earth, nor any one part of this 
 fyftem can furTer alone, as ruin to one would, 
 perhaps, be ruin to all. 
 
 From nature's chain whatever link you (hike, 
 Tenth or ten thousandth, breaks the chain alike. 
 
OF COMETS, PS 
 
 It has been faid above, that 450 comets are re- 
 corded in hiftory. Now if we confider, that mod 
 of thefe comets defcend more or lefs, into the 
 fphere of the orb of the earth; and that out of 
 thofe whofe orbits have been calculated, there are 
 only fix whofe leaft diftance from the fun, ex- 
 ceeds that of the earth, — yet ftill, no accident 
 has happened that we can trace in the hiftory of 
 the moft remote ages of the world : — May we 
 not fuppofe, that room enough is afligned in infi- 
 nite fpace, by infinite power, for thefe orbs to 
 move in, without falling foul of each other, as if 
 left to the guidance of blind and blundering chance ; 
 and that we have nothing to apprehend from fhort- 
 fighted predictions, or fanciful hypothefes. 
 
 It is therefore to prevent too great difturbances 
 in the motions of comets from the acYion of the 
 planets and other comets, fays Sir Ifaac Newton, 
 that while the planets revolve all of them nearly 
 in the fame plane, the comets are difpofed in ve- 
 ry different ones, and diftributed over the whole 
 fyftem. 
 
 Maclaurin, too, has an admirable reflection 
 upon this fubject, in his paraphrafe on Sir Ifaac 
 Newton's Principia. Speaking of the fatal effects 
 that feemed poffible to happen from the near ap- 
 proach of the great comet of i 680 to the earth, 
 
94 THE HISTORY 
 
 fays, " it is not to be doubted but that, while fo 
 many comets pafs among the orbits of the planets, 
 and carry fuch immenfe tails along with them, we 
 mould have been called by very extraordinary con- 
 fequences, to attend to thefe bodies long ago, if 
 their motions in the univerfe had not been at firft 
 defigned and produced by a being of fufficient fkill 
 to forefee their diftant confequences." 
 
 The prefent comet totally difappeared about the 
 I 6th, being immerged in the rays of the fun, paf- 
 iing with great rapidity to its perihelion, from 
 whence we are now (October) impatiently expect- 
 ing its return. 
 
 By an article from Paris we are likewife inform* 
 ed that it became invifible there the fame day on 
 which it retired from us. 
 
 " The late comet, fo much talked of, was dis- 
 covered at Paris the 8 th of la ft Auguft, by that 
 indefatigable aflronomer, M. MefTier, whofe afli- 
 duity and dexterity in obferving the heavenly bo- 
 dies, have long fince deferved the higheft praifes 
 from the learned ; and he was honoured on this 
 prefent occafion with a letter, wrote to him upon 
 the fubjecl, by one of the greateft raonarchs in 
 Europe, and geniufes of this age. The accurate 
 obferver followed obferving the courfe of the co- 
 met till the i 6th of September, when it ceafed to 
 be viflble by its approaching to the fun, being then 
 
OF COMETS. 95 
 
 near the alpha of Hydra. Its elements have been 
 calculated by M. de la Lande, upon three equi- 
 diftant obfervations of M. Meflier, made on the 
 14th, 2 1 ft, and 28th of Auguft, and are as 
 follows :" 
 
 " Inclination of the orbit, 73 deg. 15 min. 
 Defcending node, 1 1 fign. 2 6 deg. 2 3 min. Peri- 
 helion, 6 fign. 1 1 deg. 2 8 min. PafTage at the 
 perihelion the 1 ft of October, at 9 and 2 2 min. 
 Diftance of the perihelion, 0,03104; that is to 
 fay, 32 times nearer to the fun than our globe ever 
 is. From this it appears, that this comet does not 
 refemble any of the 57 comets we know of; on- 
 ly the two feen in the years 1680 and 1689, 
 did approach neareft to the fun. The laft of them 
 mould have fome likenefs to this, were it not for 
 the great difference between the diftances of their 
 refpeclive perihelions, which take away any fufpi. 
 cion of this being the fame." 
 
 According to the perihelion diftance given to 
 this comet by M. de la Lande, it might have 
 been expected to return fooner than has been found 
 by experience, as the velocity it would have ac- 
 quired by fuch a near approach to the Sun, would 
 have been accelerated, and its trajectory dimi- 
 nished. 
 
 As this comet, in its way to the Sun, fets weft* 
 
96 THE HISTORY 
 
 ward of that luminary, it will rife from its rays on 
 the other fide ; namely, eaftward of the Sun. 
 
 There is a popular divifion of comets into three 
 kinds; namely, tailed, bearded, and hairy comets, 
 though this divifion rather relates to the different 
 circumftances and fituations of the fame comet, 
 than to the phenomena of feveral. 
 
 Thus, when the light is weftward of the Sun, 
 and fets after it, the comet is faid to be tailed, be- 
 caufe the train follows it in manner of a tail. 
 
 When the comet is eaftward of the Sun, and 
 moves from it, the comet is faid to be bearded, 
 becaufe the light marches before it in manner of a 
 b ard. 
 
 And laftly, when the comet and the Sun are 
 diametrically oppofite, (the Earth between them) 
 the train is hid behind the body of the comet, ex- 
 cept a little that appears round it, in form of a 
 border of hair* 
 
 The tails of comets are always on the fide op- 
 pofite to the Sun. This was. firft difcovered by 
 Appian, and has fince been conftantly confirmed by 
 obfervation. They are belt feen, and appear 
 longeft in fouthern climates, where the air is pure 
 and fky ferene. The comet of 1759 appeared 
 at Paris almoft without a tail, and in England 
 
 * From this laft appearance the word comet is derived; as 
 JHofirnrig, Cometa, comes from Ko^w, Coma^ a head of hair. 
 
OF COMETS. 97 
 
 entirely without one. At the former place, it 
 was with great difficulty that a flight trace of one 
 could be diftinguifhed of only one or two degrees 
 in length ; whereas at Montpelier, M. de Ratte 
 found it to have one, April 29, of 25 degrees 
 in its whole length, and 10 degrees of it extreme- 
 ly luminous ; but M. de la Nux faw that comet, 
 at the ifle of Bourbon, with a tail much more 
 confiderable ; for the fame reafon that the zodiacal 
 light is always vifible there, and extends to above 
 100 degrees in length. 
 
 But there have been jomets, whofe difk was as 
 round, as well defined, and as clear as that of Ju- 
 piter, without either tail, beard, or coma ; fuch 
 was one of the comets that appeared in 1 66$, 
 and, according to Caffini, that of 1682. Hence 
 the tail of a comet muft not always be regarded 
 as its neceflary appendage, or principal charac- 
 teriftick. 
 
 Moft comets are vifibly furrounded with an e« 
 normous atmofphere, often rifing ten times high* 
 er than the nucleus, or folid body of the comet. 
 Sir Ifaac Newton fuppofes it to be owing to the 
 atmofphere of a comet, that the nucleus is ufually 
 fo ill defined ; the moll: lucid parts of which not 
 being above a ninth or tenth part of the whole 
 breadth. In obfervations upon comets, it is common 
 to meet with accounts of bright fpots in the mid- 
 I 
 
oS THE HISTORY 
 
 die of the nucleus, when in fact it mould feem that 
 the bright fpot only was the nucleus, and the reft 
 the atmofphere of the comet. 
 
 M. de la Lande fuppofes very ingenioufly, that 
 as comets are deftined to pafs from the moil 
 dreadful rarefraction and heat imaginable, to a 
 cold denfity beyond conception, they are provided 
 with thefe immenfe atmofpheres, not only to pro- 
 tect them from fuch defhuctive exceffes, but like- 
 wife to fupport and foment circulation, fluidity, 
 motion, and life. 
 
 It has been remarked that comets have different 
 phafes, like the Moon; and it was obferved by 
 CafTini, in the year I 744, that the body of that 
 comet was horned, mewing only half its difk. 
 
 The prefent comet, feen through a good tele- 
 fcope, feems more to refemble a fmall Moon than 
 a fixed frar. The nucleus, or body of it, is large, 
 but ill defined. The phaenomena of the tail feems 
 fo much to favour an ingenious conjecture in the 
 Monthly Review, (Oct. 1767, p. 253.) that we 
 cannot refill: quoting it. 
 
 The book under examination is Dr. Prieftley's 
 Hiftory of Electricity : " Signior Beccaria has, 
 with great ingenuity, mixed fometimes with a little 
 fpice of agreeable extravagance, the frequent con- 
 comitant of genius, ranged almoit all the meteoric 
 phenomena under the banners of electricity ; from 
 the Will tf-ttiWifp up to the Aurora Borealis. 
 
O F C O M E T S. 99 
 
 Had we room or inclination to theorife on this fub- 
 ject, at the fame time that, with other electricians, 
 we allowed the electric fluid to be the caufe of 
 this laft phenomenon, we mould be for extending 
 its connections ftill further, and attempt to mew 
 the poflibility, at leaft, of its near relation to, if 
 not its identity with, that luminous matter which 
 form3 the folar atmofphere, and produces the phae- 
 nomenon called the Zodiacal Light ; which is 
 thrown off principally, and to the greateft diftance 
 from the equatorial parts of the Sun, in confe- 
 quence of his rotation on his axis, extending vi- 
 fibly, in the form of a luminous pyramid, as far 
 as the orbit of the Earth ; and which, according 
 to M. de Mairan's ingenious, and, at leaft, plau- 
 fible hypothefis, falling into the upper regions of 
 our atmofphere, is collected chiefly towards the 
 polar parts of the Earth, in confequence of the 
 diurnal revolutions, where it forms the Aurora 
 Borealis. It would, we think, be no very bad 
 hypothefis which mould unite thefe two opinions, 
 by confidering the Sun as the fountain of the e- 
 lectric fluid, and the zodiacal light, the tails of 
 comets, the Aurora Borealis, lightening, and arti- 
 ficial electricity > as its various, and not very dif- 
 fimilar modifications." Indeed the appearances of 
 the tail of this comet refembled electrical corufca- 
 tions, more than any thing of which we have an 
 
 I 2 
 
ioo THE HISTORY 
 
 idea, but moftly that produced in vacuo ; as the 
 flame feemed, through a telefcope, perpetually 
 to (hoot out in ftrait lines, of a pale filver hue, 
 lengthening and fhortening at each inffont, and 
 forming frequently fome of the configurations 
 which the Aurora Borealis aiTumes. 
 
 There has been lately published a work by Dr. 
 Hamilton of Dublin, under the title of Pbilofo. 
 phical Etfays ; in which this idea feems extreme- 
 ly well developed. The fubjecl and fubftance of 
 the Doctor's fecond efTay is fo full to our purpofe, 
 that we (hall conderfe it into an epitome, and 
 prefent it to our readers. 
 
 Dr. Hamilton's EfTay has for title, Obfervations 
 and conjectures on the nature of the Aurora Bo- 
 realis, and the tails of Comets. 
 
 The author differs from Sir Ifaac Newton, con- 
 cerning the nature of the tails of comets ; and en- 
 deavours to prove that they are compofed of a lu- 
 cid, or felf-fhining fubftance, and not a mere cloud 
 or vapour, illuminated only by the Sun. This 
 luminous matter he fuppofes to be the fame with 
 that which caufes the Aurora Borealis, and the 
 phaenomena of electricity. 
 
 " The great body of luminous matter which 
 appears in an Aurora Borealis, fays this Author, 
 being fo very extenfive, and fometimes fo very 
 bright, muft be vifible to a fpeclator at a confide- 
 
OF COMETS. 1 01 
 
 rablc diftance from the Earth, and fhaded from 
 the Sun's light ; and fuch a fpettator would then 
 fee the earth attended by a train of light in the 
 form of a tail" 
 
 " Electric matter appears to be of the fame 
 kind of fubflance which forms the Aurora Borea. 
 lis t and the tails of Comets ; by its having alfo 
 that remarkable property of letting the rays of 
 light pafs through it, without having any fort of 
 effect upon them/' " Now the extraordinary 
 rarity of comets tails may be collected, fays Sir 
 Ifaac Newton, from the frars mining through 
 them ; for the fmalleft ftars are obferved to mine 
 without lofs of fplendor through tails which are of 
 an immenfe thicknefs." (Principia, p. 513, 
 edit. 2 .) Dr. Hamilton has given to comets a 
 quite different employment from that allotted to 
 them by Sir Ifaac Newton, who made them wa- 
 ter carriers, loading them with vapours and moi« 
 fture, to fupply the loffes of the feveral parts of 
 the folar fyftem through which they were defined 
 to pafs. But the Doctor, on the contrary, fup- 
 pofes it their bufinefs to collect and bring back to 
 the Sun and planets, the electric fluid which is con- 
 ftantly flying off into the higher regions of the 
 heavens, beyond the orbit of Saturn. " We fee 
 this fluid rifes from the earth into the atmofphere, 
 and is probably going off from thence, when it 
 
 1 3 
 
102 THE HISTORY 
 
 appears in the Aurora Borealis. And as this elec- 
 tric matter, from its vaft fubtilty and velocity, 
 feems capable of making great excurflons from 
 the planetary fyftem, the feveral comets in their long 
 excurflons from the Sun, in all directions, may 
 overtake this matter, and attracting it to themfelves, 
 may come back replete with it, and being again heat- 
 ed and excited by the Sun,maydifchargeanddifperfe 
 it among the planets, and fo keep up a circulation 
 of this matter, which we have reafon to think ne- 
 ceffary in our fyftem." 
 
 This does not feem far from Sir Ifaac Newton's 
 own opinion : for after fuppofing that the aque- 
 ous particles thrown off from comets are taken up 
 by the planets, as a fupply of moifture, he adds,* I 
 ' fufpecl, moreover, that that fpirit which is the 
 ' leaft, but the mod fubtile, and the bed part of 
 < our air, and is necefTary for fupporting the life 
 * of all things, comes chiefly from the comets.' 
 
 Dr. Halley, fo long fince as the year i 7 1 6, in 
 his description of a remarkable Aurora Borealis, 
 fays, " That the great ftreams of light fo much 
 refembled the tails of comets, that at firft fight 
 they might well be taken for fuch ;" and after- 
 wards adds, " This light feems to have a great af- 
 finity to that which the effluvia of electric bodies 
 emit in the dark." This was the doctor's conjec- 
 ture ; — but both he, and Sir Ifaac Newton, had 
 
OF COMETS. 103 
 
 fo much of vaticination in all they faid, that their 
 conjectures are found by pofterity to be little lefs 
 than certainties. 
 
 But this ftriking fimilarity between the appear 
 ances of the tail of the comet in a telefcope, the 
 Lumen Boreale, and the electric flam, was fuggeft- 
 ed to the writer of this hiftorical (ketch by the 
 phaenomena themfelves, and not by the paflages 
 juft quoted, of which he had not the leaft know- 
 lege till after he had formed his opinion on the 
 fubje£t, but which indeed he was glad to have for- 
 tified by fuch good authorities. 
 
 It is with diffidence he mentions another telef- 
 copic appearance, as it may perhaps be only an 
 optical illufion. It feemed perceptible that the 
 nucleus of the comet had a very rapid motion on 
 its own axis, and that there was a conftant emiifion 
 of electric fparks, or flames from it at all points, 
 which were inftantly impelled with great violence 
 towards the tail. 
 
 It has not as yet been pofitively determined by 
 aflronomers, whether this prefent comet is one of 
 thofe that have ever viflted us before, at leaft fince 
 comets have been fo narrowly watched. But it is 
 hoped that the worthy fucceflbr of the great Flam- 
 Head, Halley and Bradley, by whom this comet 
 will doubtlefs have been well obferved, will clear 
 up this point, when he fhall have had fufficient lei- 
 
104 
 
 THE HISTORY 
 
 fure for computing its elements, and comparing 
 them with thofe of other comets already computed. 
 Out or above 50 comets whofe elements are 
 known, the returns of no more than 5 or 6 have 
 been foretold : which may be feen in the following 
 table. 
 
 Former Appearances. 
 
 1531: 1607 
 
 76 
 
 174 
 169 
 44Ant.C.53i : notf :i68o 575 
 
 •1531 : 1661 
 i68z : 1759 
 ■■ ■■ 1164: 1556 
 1165 : 1338: iju : 1686 
 1593 : 1 7<Sx 
 
 Years 
 Period 
 
 Return] Orbits by whom 
 
 expec. 
 about I 
 
 178: 
 1834 
 1848 
 i860 
 1931 
 ax55 
 
 calculated. 
 
 Halley. 
 
 Halley. 
 
 Halley. 
 
 Pingre. 
 
 La Caille Pingre 
 
 Newton, Halley. 
 
 The comets that are firft expected, are placed 
 firft in the table. But it may be neceflary to give 
 the authorities upon which this table is conftruc- 
 ted. 
 
 The comet of 1661 obferved by Hevelius, and 
 that of 1 532 by Appianus, (though there is a con- 
 fiderable difference in the places of their periheli- 
 ons, which may eafily be attributed to the imper- 
 fect and unfkilful manner in which it was obferv- 
 ed by Appianus) may be the fame; and if Halley's 
 conjecture be well founded, this comet will again 
 appear in the year 1789 or 1790. (#*/?. des 
 Mat. par Montucla.) 
 
OF COMETS. 105 
 
 Of the fecond comet enough has already been 
 faid, under the article I 759. Unlefs we here be- 
 ftow a few words upon the memory of M. Clai- 
 raut, who died May 3, 1 765, aged but 52 years! 
 in his elogium juit publilhed in the Hift % de VArcad. 
 des Sciences, there is this paiTage, equally apper- 
 taining to that great geometrician and to rhis ar- 
 ticle. — * Thanks to his labours ! the opinion that 
 ' comets are planets, as ancient as the world it- 
 ' felf, is now no longer a conjecture, but is re- 
 * garded as a thing fully demonurated.' 
 
 For the account of that which has the third 
 place in the table, we are indebted to Mr. Dun- 
 thorne, (Phil. Tranf. vol. 47.) who conjectures, 
 that if the comet which appeared in 1 2 64 be the 
 fame as that which was obferved by Paul Fabricius 
 and others in the year 1 $$6, and whofe orbit Dr. 
 Halley has compared, its period will turn out as 
 above. 
 
 Concerning the comet which occupies the fourth 
 place in the table, we are indebted to M. Struick, 
 who, in his fequel to the defcription of comets, 
 (Amft. 1 753) fuppofes the comet of 1 68 6 to be 
 the fame as that of 1 5 1 2 ; "for one is upon re- 
 cord in 1 338, — in 1 1 65, — in 990, — in 8 1 7, 
 — and in fhort 870 years before, that is to fay, 
 at the diftance of 5 times 1 74 years ; 53 years be- 
 fore Chrift." 
 
106 THE HISTORY 
 
 Our authority for the fifth comet in the table, 
 is given in the article for the year 1762. 
 
 And about the fixth or great comet of 1 680, 
 which fo alarmed the inhabitants of our globe in 
 the laft century, though the prefent is but little in- 
 terested, fo diftant is the period : " Yet, if it re- 
 turn in 2255," fays Maclaurin, " it will give a 
 new lufrre and evidence to Sir Ifaac Newton's 
 philofophy, in that remote age. And mould the 
 inconftancy of human affairs, and the perpetual 
 revolutions to which they are fubje£r, occafion 
 any neglect of our philofophy in the interven- 
 ing ages ; this comet will revive it, and fill every 
 mouth again with this great man's name. For it 
 is one of the good effects which thefe great periods, 
 and diftant depending obfervations promife, that 
 they muft contribute to preferve the relifh for 
 learning from the revolutions to which it has been 
 formerly fubject. By them, diftant ages are con- 
 nected together, and perpetual matter is provided 
 from time to time, for reviving the curiofity of 
 mankind." 
 
 And though the returns of no more than fix 
 comets have, as yet, been calculated and foretold 
 by aftronomers; yet, from the elements laid down, 
 every age will recognize fome of thofe which have 
 vifited us before ; till at length, the whole num- 
 ber of comets in the folar fyftera will be as well 
 
OF COMETS, 107 
 
 known to the inhabitants of the earth, as the five 
 planets and their fatellites. 
 
 One of them is already added to the number of 
 revolving planets, which it is hoped will leflen the 
 popular dread at the appearance of the reft. At 
 this time of day it feems fcarcely neceflary to fay, 
 that the experience of many thoufand years aflures 
 us that the folar fyftem is fo wifely framed and re- 
 gulated, as not to be fubject to accidents from the 
 approach of comets. But as two fuch able aftro- 
 nomers and mathematicians, as Whifton and Gre- 
 gory, feem to encourage the belief that general 
 ruin, or at lead: dreadful calamities, may be the 
 confequence of a near approximation to the tail of 
 a comet, and as their opinions have no other foun- 
 dation than conjecture and fpecuiation, we may 
 venture, without arrogance, to conjecture and 
 fpeculate in our turn. 
 
 And firft, let us fpeak to Mr. Whifton, who 
 having (as has been mentioned in M. Maupertuis's 
 Letter) with great learning and labour traced the 
 great comet of I 680 by different periods, of $j 5 
 years, up to the univerfal deluge, endeavours to 
 account for that terrible cataftrophe, by the water 
 that was brought into our atmofphere by the tail 
 of that comet. We will, for a moment, grant 
 it poffiblefor comets to quit the regular and ftated 
 courfe originally afligned them, and likewife, for 
 
Io8 THE HISTORY 
 
 the fake of Mr. Whifton's hypothefis, fuppofe the 
 tails of comets to be compofed of aqueous vapours 
 (an opinion, which, with Dr. Hamilton's affiftance, 
 we have endeavoured to confute) yet (till a power- 
 ful objection to the deluge having been occafion- 
 ed by the tail of the comet remains ; namely, that 
 vapours at fuch a great di fiance from the earth 
 would be fo rarified, that notwithftanding the co- 
 met of i 744 had a tail 40 degrees long, the pre- 
 fent comet one of 42, and that of 1 680 one of 70 
 degrees in length — if all the waters of this enor- 
 mous tail were comprefled into the denfity of thofe 
 vapours in our atmofphere, which, coalefcing, com- 
 pofe rain; they would be infufficient for the pur- 
 pofe of drowning the earth : fince a fingle drop 
 of water, rarified into vapour in ourgrofs atmof- 
 phere, occupies 14,000 times the fpace it did, 
 when condenfed into water ; and vapours fuffici- 
 ently rarified to fwim in iEther, though they form- 
 ed a volume equal to the orbit of the Earth, would 
 not furnifh water enough to overwhelm it, which 
 Sir Ifaac Newton has demonftrated by proving that 
 a cubic foot of water, at the diftance of a femi- 
 diameter of the earth, would be fo rarified as to 
 occupy a fpace equal to the orbit of Saturn. 
 
 It has been faid above by M. Maupertuis, that 
 Dr. Gregory has eftablimed the comets again in 
 all their terrors. In fuppofing fuch dreadful com- 
 
OF COMETS. 109* 
 
 fequences from a comet's tail being in contact with 
 our earth, &c. — if the learned Doctor were ftill 
 living, one would be inclined to afk him, why 
 the poor old ladies arc ftill to be frightened with 
 comets I Do they either portend or occafion any 
 thing worfe than always fubfifts ? When was the 
 world without its plague, peftilence and famine ; 
 battle, murder and fudden death ? Though co- 
 mets are doubtlefs placed in the heavens for fome 
 wife purpofe, wholly infcrutable to us, yet, for 
 any thing we have hitherto difcovered, they have 
 no more influence or effect upon our globe, or 
 its inhabitants, than a will-6 t ~th > - t wijp or ignis fa- 
 tuus ; — and yet every thing that is mifchievous 
 or difagreeable is placed to the account of the 
 poor comet. — If it rains, " it is the comet ;" — if 
 the weather be hot, " it is the comet ;" — if it be 
 cold, it is the fame. — Pray let us be a little equi- 
 table, and allow that fuch things, as abundant rain, 
 intemperate heat, and intenfe cold, have happen- 
 ed in this climate before now, without the agen- 
 cy of a comet ; unlefs by fome comet that has ap- 
 peared in difguife, like Mr. Bayes's army.' 
 
 " The war in the weftern parts of Europe, 
 which continued from the year 1688 to 1697, 
 has been the moft obftinate and deftruclive of any 
 recorded in hiflory ; and yet no comet has ap- 
 peared, either immediately before or after ; but 
 K 
 
no THE HISTORY 
 
 on the contrary, one has been feen in September, 
 1698, when Europe was already freed from this 
 war, and was on the point of eftabliming a lading 
 peace between the Chriftians and Turks. — A comet 
 therefore has appeared between two treaties of peace, 
 which have put an end to the ravages of war, in 
 all parts of Europe, and greatly changed the gene- 
 ral fituation of affairs for the better : A comet 
 which reftores thofe happy times, in which the 
 temple of Janus is mut." (Penjees div. fur la co- 
 mete de 1 680)- 
 
 But fuperftitious people love to be frightened, 
 and will be as angry with any one who endeavours 
 to reafon them out of their fears, as the inhabi- 
 tants oi Neuf Chatel were lately with one of their 
 paftors, who, though in other refpetts an ortho- 
 dox and devout Chriftian, yet could not reconcile 
 to his belief the eternity of hell torments. — He 
 would allow them to laft a hundred thoufand years, 
 with all his heart, — but that would not fatisfy his 
 flock, — they profecuted, perfecuted, and pelted 
 him. "When the king of Pruflia, their fovereign, 
 hearing of it, and moreover that theininifter was a 
 worthy, well-meaning man, ordered them to de- 
 fift, and fufTer him to refume his function. But 
 this enraged them ten times more, — they fur- 
 rounded the good man's houfe, and would cer- 
 tainly have fent him to the other world, to enquire 
 
OF COMETS, in 
 
 into the true ftate of departed foujs, had he not 
 with great difficulty made his efcape; and, at 
 length, their fovereign, finding how fond they 
 were of everlafting damnation, out of his great 
 goodnefs, condefcended to let them be damned to 
 all eternity. — " And I alfo, (fays the author 
 from whence this account is taken) confent with 
 all my heart, and much good may it do them." 
 — Lettre de M. Baudinet. 
 
 It is amazing that fuch as are always ready to 
 denounce divine vengeance, and to prefage every 
 fpecies of calamity to the frighted inhabitants of 
 the globe, upon the appearance of a comet; — 
 that they, whofe belief of the interpofition of a 
 particular providence upon every trivial occafion, 
 is fo firm, never (hould think of extending their 
 faith to the belief of a general providence, which 
 has fecured the globe from contingent evils ! 
 
 But there yet remain many who will have it 
 
 that (t a comet never appears without blood," 
 
 and are fure to be right in their conjectures. For 
 if Europe fhould enjoy a profound peace, they 
 have only to look at Afia ; and if all be quiet 
 there, they have ftill the other two quarters of 
 the globe to fly to, which will, doubtlefs, furnifh 
 them not only with carnage enough, but alfo 
 with every other kind of evil, both phyfical and 
 K 2 
 
H2 THE HISTORY, etc. 
 
 moral, their hearts can wi(h, to confirm them in 
 their opinion. 
 
 But thofe who are unwilling to fee God, but 
 in vengeance and diftruction, mould try to difco- 
 ver him in his goodnefs and protection from ge- 
 neral calamity, by that wife order of his providence, 
 fo vifible in the wonderful and ftupendous arrange- 
 ment of the univerfe. 
 
 postscript. 
 
 London, Oct. 25. 1769. 
 
 THE comet is returned. — It was feen laft 
 Monday, by feveral people, in different 
 parts of the kingdom, at half an hour paft fix in 
 the evening ; weft: by fouth, about nine degrees 
 high. It appears with a Coma, but without a tail : 
 perhaps the tail may be vifible in a clearer air. 
 The comet is at prefent more diftant from us than 
 the Sun, and its tail oblique to us, whereas, in 
 its former appearance, it was perpendicular. 
 
 THE END. 
 

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