A Letter from Mr. Rich. Dunthorne to the Rev. Dr. Long, F. R. S. Master of Pembroke-Hall in Cambridge, and Lowndes's Professor of Astronomy and Geometry in That University, concerning Comets

sure me, this lad has a sister about ten years of age in the same declining state. I am, Dear Sir, Yours most affectionately, John Browning. As new-born children frequently exceed in weight this youth of fifteen years, I take the liberty to communicate his case, believing it will not be thought incurious. H. Baker. XLIII. A Letter from Mr. Rich. Dunthorne to the Rev. Dr. Long, F. R. S. Master of Pembroke-Hall in Cambridge, and Lowndes's Professor of Astronomy and Geometry in that University, concerning Comets. SIR, Cambridge Oct. 5, 1751. Read Nov. 14, 1751. THERE is a manuscript in your college library, chiefly astrological, wherein there are five tracts of different authors concerning comets. One of them, intitled, Tractatus fratris Egidii de cometis (written on account of a comet, which appeared in the year of our Lord 1264.) contains these passages relating to its place and motion: N n Prolog. Prolog. "Stella caudata seu crinita apparuit in regno Franciae in oriente ante solis ortum a 19° kalendaras Augusti usque 5° nonas Octobris in anno Domini 1264. Cap. 1. "Cometem, cujus occasione haec scripsimus, primo vidimus extra circulum zodiaci versus aquilonem contra cancrum, et demum eundem vidimus extra circulum versus austrum sub geminis inter canem et orionem. Cap. 3. "Vidimus autem et stellam caudatam, cujus occasione hoc scripsimus, praeter motum circularum diurnum, æque moveri motu retrogradationis, et nulli alii similis, secundum latitudinem ejus, quæ est a septentrione ad austrum. Visus est moveri per duos menses solares plusquam 40 gradus, vix per 3 gradus longitudinis permutans situm. Cap. 7. "Cometes, cujus occasione haec scripsimus, primo visa est in vespera post solis occasum, demum post paucos dies solem pertransiens in mane circa octavum gradum cancri, et ex hinc cito processit retro in geminos: ——— vidimus autem et cometem moveri ab aquilone ad austrum, secundum latitudinem quidem plus 50 graduum, et secundum longitudem quidem vix 5 gradus processisse." Hevelius in his Cometographia has also given us the following paragraph, among others, concerning this comet: "A.C. 1264, stella, quæ dicitur cometes, apparuit, videlicet in oriente, ante ortum diei, post stellam matutinam: apparuit, scilicet, ante auroram cum radiis multis: ipsi ejus radii longe lateque apparuerunt "appartierunt antequam oriretur ipsa stella cometes. "Igitur veloci cursu laboravit ipsa stella cometes, ita "quod praecurrerit & longe versus meridiem praecessit "stellam matutinam, i.e. luciferum. Visa est circa "festum S. Mariæ Magdalenaæ, & usque ad octavam "S. Augustini apparuit. Compilat. Chronol." Although this whole account be very slender and rude, it is however much the best I have met withal of any comet earlier than that, which was observed by Regiomontanus in the year 1472 (except perhaps the account given us by Nicephorus Gregoras of the comet of the year 1337, whose orbit is computed by Dr. Halley): for which reason, I was induced to try whether I could investigate a set of elements capable of representing the places of this comet agreeable to the above description, and after several attempts, some of them indeed but tentative, I fixed upon the following numbers for that purpose, viz. the place of its ascending node in \( \text{Nr} \) 19°, the inclination of its orbit to the plane of the ecliptic 36°½, the place of its perihelion in \( \text{Nr} \) 21°, its perihelion distance from the sun 44500 such parts as the mean distance of the earth from the sun contains 100000, and the time of its being in perihelion July 6th 8th p.m. The motion of the comet in this orbit was direct. Its places computed from these elements are as in the following table. | Nn | Time | |----|------| | | | | Time | Comet's long. | Comet's latit. | |--------------|---------------|----------------| | July 1 in the evening | 25° 57' | 22° 13' North | | | | | | 14 in the morning | 7° 58' | 10° 49' | | 18 | 4° 8' | 5° 2' | | 22 | 1° 40' | 0° 30' South | | 26 | 0° 16' | 5° 31' | | 30 | 29° 35' | 9° 59' | | Aug. 3 | 29° 21' | 13° 58' | | 7 | 29° 23' | 17° 30' | | 11 | 29° 34' | 20° 42' | | 15 | 29° 49' | 23° 39' | | 19 | 0° 2' | 26° 23' | | 23 | 0° 12' | 28° 58' | | 27 | 0° 17' | 31° 24' | | 31 | 0° 16' | 33° 42' | | Sept. 4 | 1° 35' | 56° | | 8 | 29° 36' | 38° 4' | | 12 | 29° 0' | 40° 6' | | 16 | 28° 12' | 42° 4' | | 20 | 27° 7' | 43° 55' | | 24 | 25° 46' | 45° 41' | | 28 | 24° 8' | 47° 18' | | Oct. 3 | 21° 44' | 49° 8' | * Perhaps the tail might not be conspicuous enough to occasion its being taken much notice of, in its descent towards the perihelion. † July the 6th, the comet was in the same right ascension with the sun, and had near 41° ½ north declination; so that in the south of France it set about the going down of twilight, and did not rise again till day-break; and therefore might escape being seen for a few days, either morning or evening, about this time. I think I think the computed places here set down agree as well with the foregoing description as any regular computus can be expected to do; and the resemblance of all the elements gives some ground for conjecture, that this comet might possibly be the same with that which was observ'd by Paul Fabritius and others in the year 1556, whose orbit Dr. Halley has computed: See his Synopsis Astronomiae cometicae. Indeed the change in the place of the perihelion may perhaps be thought greater than could arise from the mutual gravitations of the comets disturbing one another; but then it may be consider'd, that neither the place nor time of the perihelion, nor the perihelion distance of the comet of the year 1556, could be determined very accurately from observations made only for 12 days, at 40 days distance from the perihelion, as those of Fabritius were, unless they had been more exact than his appear to be. If these were one and the same comet, its period is 292 years; and we may expect its return about the year 1848. There are in the before-mention'd manuscript, besides the passages already quoted from Egidius, two other places which deserve to be taken notice of. One of them is so much of a small tract, intituled, Judicium de stella comata anno Domini 1301, as concerns the place and motion of the comet; it is as follows: "A.D. MCCC primo, primo die Septembris appa- "ruit cometa in occidente, et per mensem vel am- "plius visus fuit. — Ultima autem die Septembris "duabus horis 40 minutis post occasum solis — in- "veni quod longitudo cometæ in signis et gradibus "erat "erat 20 gradus scorpionis, et latitudo * 26 gradus septentrionalis: Mars autem tunc erat in 20 gradu scorpionis directus exeuns, et sic fere conjuncti erant Mars et cometa accipiendo loca ipsorum per circulum transeuntem per polos zodiaci. — Verum et sexta die Octobris, scilicet in festo Sanctae Fidis post occasum solis eadem hora inveni quod longitudo ejus erat primus gradus sagittarii, et latitudo ejus 10 gradus septentrionalis. — Cometae latitudo ecliptica circa principium apparitionis suae fuit 20 gradus et amplius septentrionalis. — Apparebat coma moveri a septentrione in meridiem per oriens, ita quod ejus longitudo orientalis continue videbatur augeri, et ejus latitudo septentrionalis continue videbatur diminui. — In principio apparitionis suae coma protendebatur ad septentrionem; et post motum successive movebatur per orientem ad meridiem versus stellam quae dicitur altayr hoc est vultur volans." Though this account is too imperfect for us to attempt determining the orbit therefrom, it may notwithstanding help us to know the same comet again, if any should hereafter appear whose orbit will agree with this relation; which I believe none of those already computed will do. The other place I hinted at as worthy of notice, is this short passage in a treatise De significatione cometarum: "Et * This figure (2) is a different writing from the rest of the manuscript, and has manifestly been alter'd since it was first written; it seems to have been 16° at the first, which I think the truer reading. "Et nos invenimus modo quod apparuit intempore nostro unus cometa in principio piscium, et cauda attingit usque ad principium geminorum in nocte Mercurii, et hoc fuit in ultimam nocte Junii, anno 499 Arab. et sequebatur ordinem signorum quo- usque venit usque ad principium cancri, et dimisit ordinem signorum, et incepit deficere." The word Junii here found seems to have been transcribed by mistake for the Arabic month Jumedi.j, the last day whereof that year was Wednesday Feb. 7. A. C. 1106; whereas the last day of June fell upon Saturday. This reading agrees with the following notes concerning the same comet collected by Hevelius in his Cometographia, p. 821. "A. C. 1106 a prima hebdomada quadragesimae cometam immensi fulgoris usque ad passionem Domini conspeximus." Lavath ex Ursburg. "A. C. 1106, mense Februari. biduo post novilunium, visus est magnus cometa, ad occasum solis brumalem." Calvis. ex Tyr. The new moon was Feb. 5, Ash-Wednesday that year Feb. 7, and Good-Friday, March 23. If we suppose (with Dr. Halley) this comet to be the same with that which appeared in 1680, and that it was in perihelio Feb. 4, at noon (for it must have been seen in two or three days after it had passed its perihelion) some of its places would have been there: Feb. The wide disagreement there is between the manuscript account of this comet, and its places here computed, must very much lessen, if it does not quite overbalance, the force of the arguments brought by Dr. Halley to prove the identity of these two comets. Indeed if this comet had been the same with that of 1680, it could not have come to the beginning of Cancer, without a change in the place of the perihelion too great to be easily admitted; nor could it have left the order of the signs without a change in the elements still greater. I am, SIR, Your obliged, and most obedient servant, Richard Dunthorne. XLIV.