9C2 



ASTRONOMY. 



[COMETARY BISTORT. 



A* to the light which these bodies possess, the Into M. 

 Arago inferred, from his experiment*, that they Rhine 

 it-fleeted light But, although his experiments on 

 iniet of 1819, and that of Halley in 1835, showed 

 tint they sli..no by reflected light, which be satisfactorily 

 confirmed by experiments with apolarisoope on the light 

 of stars of the same magnitude in their neighbourhood, 

 lie was rather doubtful whether they had iiot a proper 

 light of their own, since, without losing their property 

 oi reflection, some independent light might at the same 

 time reach the earth. 



So long ago as the year 837 of our era, the circumstance 

 was remarked by the Chinese annalists ; and again noticed 

 by Appian, in the ]Gth century, that the tails of comets 

 were generally directed from the sun. The appearance 

 of these accompaniments are variable, both in regard to 

 magnitude and brilliancy. Of the comet of Kits'.*, the 

 contemporary historians state that its tail occupied an 

 extent of 9W", and presented an appearance similar to a 

 Turkish sabre. The tail of the comet of 17(50, was ob- 

 served to be 97 in length. The comet of 1744 bad as 

 many as six tails, each 4 in breadth, and 30 to 44 in 

 length In our own days, th<3 appearance of the comet 

 of 1861 cannot be forgotten. At London, in -Inly, its 

 length, by observation, was found to he from 60 to 80. 

 comet of 1018 hud also a tail 104 in length. 



In addition to Halley's comet, others of nearly similar 

 period present themselves to our notice, and this re- 

 markable group consists of the following : 



1st. The comet of 1812, which was discovered by Pons 

 in that year, and only visible with the aid of a telescope. 

 Kncke, from all the observations, calculated its period to 

 be 707 years. 



2nd. The comet of 1815, discovered by Olbers, the 

 period of which has been calculated by Bessel to be 

 74 05 years. According to the investigations of Bessel, 

 the period of the next return will be retarded by two 

 years, in consequence of planetary perturbations, or it 

 would appear in 1M>1. 



3rd. The comet discovered by De Vioo in Rome, in 

 1846, Feb. 20, and observed till April. The calculations 

 of De Vioo and 1'eira, show that its orbit is decidedly 

 elliptical, and that its period is upwards of 70 years. 

 The only comet in the list of calculated orbits, similar to 

 this body, is that of 1707. 



4th. The next comet, nearly identical in period, is that 

 discovered by Brorsen on July 20, in Triangularus, and 

 observed at several places for the space of one month. 

 Elliptic elements, compiled by D' Arrest, give its period 



Another comet of long period, but the elements of 

 which are not so well worthy of confidence, is that dis- 

 covered by Fbunsteed in 1003. Elliptical elements of 

 this body, which are, however, too uncertain to be much 

 relied on, assign to it a period of 187 '5 years. 



Several other elliptical orbits have been calculated, 

 which will appear in a table at a subsequent page. 



The most remarkable periodical comet (which there is 

 a great reason to believe to be such, from the strong 

 identity of the elements) is that discovered by F.-ibncius, 

 in 1.Y56, and which is considered to bo a second appear- 

 ance of the fine comet of 1204. Necessarily rude as the 

 observations of this period were, Pingre and Dunthorne 

 have calculated its elements from its recorded path, 

 which agree in every particular with the comet of 1550. 

 This subject has recently occupied the attention of M. 

 Baume, who infers, from his investigations, that the comet 

 will be retarded in its return to the perihelion by a period 

 of some years. The last appearance, in 1556, was < 

 nifioent in the extreme. The tail was more than 100 in 

 length ; and, according to the Chinese accounts, it piv 

 sented a curvature similar to a sabre. It remained 

 risible till the 2nd of October of that year. There was 

 a strong probability in the inference that this body would 

 have returned to its perihelion, in the period from 1858 I 

 to 1860 ; but, as the elements are based on such uncertain 

 data, we must not be astonished at the error which its 

 absence has proved to exist. 



After thus mentioning two comets, whose periods are 



the longest on record, and the first of which has been 

 made evident by many successive returns, we shall now 

 proceed to others, whose revolutions around the sun are 

 of shorter duration. The first, and most celebrated, is 

 that of Encke. This body was discovered by Pons, at 

 Marseilles, on November 26, ISIS ; but the credit of 

 being the first calculator of its elliptic elements is due to 

 Encke, from which circumstance it bears his name. The 

 similarity of the approximate parabolic elements to those 

 comets observed in 1780, IT'."."), ami lSO."i, immediately 

 presented itself to the mind of Eucke, who likewise 

 found that a parabolic orbit would not satisfy the obser- 

 vations of 1818, 1819. Its penod is approximately three 

 years and a quarter. Since 181'.i, IH> return to the p. n 

 nelion has passed without observation ; and for this, in 

 a great measure, astronomy is indebted to the laborious 

 rah illations of Professor Encke, who furnished the ephe- 

 inerides of its predicted places. On Jtu .'. the 



comet was seen by Kumker, for the first time, at the 

 Observatory of Paramatta, in New South Wales, which 

 had then been recently founded by General Busham. 

 Although it was only observed there for a short space of 

 time, the observations were found of considerable value 

 in determining its next return in ISL'.V True to predic- 

 tion, the comet was discovered by Valz, on July 13, 

 within a short range of the calculated place. At this 

 period the comet was well observed at Naples, and other 

 European observatories. On its next arrival at its peri- 

 helion, 1828, it was first seen at Dorpat, by Strove, on 

 October 13, and was observed in European observatories 

 till December L'.V 



Although very unfavourably situated for observation 

 in the northern hemisphere, in 1832, the comet was 

 observed by Harding, at Gottingen, on August 21. Pro- 

 fessor Henderson also observed it at the Cape of Good 

 Hope ; but the observations of this return were so few 

 and scattered, that Professor Encke, in his investiga- 

 tions for its return in 1835, made no use of any of 

 them. In 1835, the comet was observed, on July 26, 

 by Boguslanzki, and previously by Kiel, at Milan,' on 

 July 22. 



In 1838, it w.is again seen by Rogusl.inzki, on August 

 14, as a very faint, shapeless object, which aft. TV, 

 increased in brightness till November. Pi nuke, 



in combining all the preceding irtunis at this period, 

 found it necessary to alter the received mass of the planet 

 Mercury, and also to allow for the effect of a resisting 

 ethereal medium, pervading all space, and which hail an 

 appreciable resistance to the cometary motions. With 

 these two important discoveries, Professor Encko pub- 

 1 an epheuiuris for its reappearance in 1842, on the 

 8th of February of which year it was observed by Dr. 

 Galle. 



Although the return of 1845 was very unfavourable, 

 the comet was seen at Rome, and in America ; but the 

 observations were so few, that no use has been made of 

 them in any investigation. 



In 1848, it was observed for a period of three months, 

 extending from August to November. The comet was 

 very faint at first, but towards November its brightness 

 increased considerably. 



In 1852, the perihelion passage took place on March 

 14, and the comet was visible on the 2nd of January. 



In 1855, the return of the comet was not favourable 

 for observation in the northern hemisphere, but it was 

 seen at the Cape of Good Hope, by Maclear. It was 

 seen in November, 1801, by Valz, at Marseilles. 



GAMBART'S COMET. This body was discovered by 

 Biela, on the 27th of February, 1826 ; but, as in the 

 preceding case, it bears the name of Gambart, who first 

 computed its orbit, and noticed its similarity with the 

 comets of 1772 and 1805. Elliptical elements calculated 

 by him and other astronomers, assigned to it a period of 

 2,400 days. In the interval of time from 1772 to 1826 

 it had performed six revolutions. The return to the 

 perihelion, in 1832, was observed generally at all the 

 European observatories. It was first seen at Rome, on 

 August 25th, as a faint object, the light of which, how- 

 ever, increased afterwards. Professor Henderson like- 



