COMETART HISTOKY. ] 



ASTRONOMY. 



963 



wise observed it at the Cape of Good Hope. On a 

 calculation of the elements of its orbit which are re- 

 presented, with the relative position of the earth, in the 

 following engraving in order to ascertain the precise 



I' A 



period of its return, it was, of course, necessary to study 

 the perturbing influence of the planets ; and when their 

 places were ascertained and compared with its course, it 

 was supposed that it would cross the earth's orbit about 

 a month before our planet was at the point of inter- 

 section. This announcement excited much curiosity and 

 some alarm. It will be evident, however, from a con- 

 sideration of its orbit, that it never came within sixty 

 millions of miles. It was a small, insignificant comet, 

 looking like a collection of nebulous matter, and having 

 neither tail, nor any appearance of a solid nucleus. In 

 the engraving, A is its perihelion and H its aphelion, B its 

 position, January 1st, 1840 ; C, on January 1st, 1833 ; D, 

 its December node ; E, its position January 1st, 1839 ; F, 

 January 1st, 1838 ; G, January 1st, 1837 ; I, January 1st 

 1836; K, January 1st, 3835; L, January 1st, 1834. It 

 will be seen from this diagram the point where the earth's 

 orbit and that of the comet intersect is very near the de- 

 scending node. The time at which the comet reached its 

 perihelion in 1832 was the middle of November ; it 

 crossed the earth's orbit on the 29th of October, but the 

 earth did not reach the same point until the 30th of 

 November. At its return, in 1839, the comet was not 

 seen from any part of the globe. In 1845, however, by 

 means of an ephemeris calculated by Professor Sautini, 

 the comet was discovered by De Vico, at Rome, on 

 November 26th, In a very short time afterwards a most 

 singular circumstance took place ; the comet appeared to 

 have been divided into two portions. This appearance 

 was first seen by Professor Wichmann, about the middle 

 of December, and generally confirmed by other observers. 

 The two nuclei were also observed till the 22nd of March, 

 1846. 



On its return to the perihelion, in 1852, the comet was 

 again seen by Professor Secchi at Rome, and at the 

 Cambridge Observatory in England. At this time, al- 

 though the predicted ephemeris was in error, both nuclei 

 were again observed, but they had separated considerably. 

 The comet at this return was exceedingly faint, and was 



only visible on nine different occasions. This and the 

 comet of Encke are comprised within the limits of the 

 solar system, and do not extend beyond the orbit of 

 Saturn. 



FAYE'S COMET. The next known periodical comet, 

 whose orbit is comprised within that of the planet Nep- 

 tune, is that discovered by M. Faye, at the Paris Obser- 

 vatory, on the 22nd of November, 1843. At its first 

 appearance it had a brilliant nucleus and tail. Faye and 

 others (Gauss included) discovered that its orbit was 

 elliptical, and that its period was 7 '2 years. At first it 

 was imagined by Argelander and Professor Henderson to 

 be the lost comet of 1770, or that of Levell ; but Lever- 

 rier has since proved that this could not be the case. 

 Its orbit at aphelion and perihelion approaches near to 

 Mars and Jupiter, and must have experienced consider- 

 able perturbations from the latter. 



M. Leverrier calculated an ephemeris for its return in 



1850, and, by means of this, the comet was observed on 

 November 28th, of extreme faintness, at the Cambridge 

 Observatory in England. With the exception of two 

 other observations obtained in the Cambridge Obser- 

 vatory (U.S), by Mr. Bond, it was not seen at any other 

 observatory. Mr. Bond described it as a very faint 

 object in the twenty-three feet refractor. 



The last four periodic comets are known as such by 

 the frequent observations of their returns to the peri- 

 helion. But others exist, whose ellipticity is equally 

 decided, although their returns have not been observed. 

 Of these, the first is the comet of De Vico, comprised, as 

 in the other case, within the planetary system, and dis- 

 covered by him at Rome, in 1844 Its period was found 

 to be 1980 days ; but although its orbit has been ably in- 

 vestigated by Dr. Briinnow, it has not been seen either 

 in 1850 or in 1855. 



BRORSE.N'S COMET. This comet was discovered at 

 Kiel, in Denmark, by Brorsen, on the 26th of February, 

 1846, and found to be elliptic, its period being upwards 

 of five years and six months ; l)rs. Briinnow and Peter- 

 sen consider that it was identical with the comets of 

 1532 and 1661. Dr. Halley, likewise, inferred the 

 similarity of these comets ; but, although expected, it 

 was not visible in 1790. It appears probable that the 

 influence of the planet Jupiter has a great effect on the ele- 

 ments of this body. Mr. Hind is of opinion that it experi- 

 enced considerable perturbations from this planet in 1842. 



D' ARREST'S COMET. This comet, whose period is six 

 years and five months, was discovered by D' Arrest in 



1851, June 27th. It suffers great perturbation from the 

 planet Jupiter in its path, and the time of its next re- 

 turn is not yet fixed. 



Another remarkable comet of this class is that dis- 

 covered by Messier in 1770, the orbit of which had been 

 calculated by Levell, indicating a period of about five or 

 six years. The planetary perturbations have, however, 

 altered the path of this comet so considerably that it 

 has never been since observed. 



Fig. 116 shows the relative orhits of four periodic 

 comets, and the comet of Halley. It must be remarked, 

 however, that the orbits are not in the same plane, and 

 that the cometary inclinations are sometimes very con- 

 siderable. In Fig. 116, A is an orbit of comets of short 

 period ; B B, the comet of seven and a half years ; C C, 

 Garnbart's comet ; E, the orbit of the earth ; H H, Hal- 

 ley's comet ; J J, the orbit of Jupiter ; M, the orbit of 

 Mars ; S, the position of the sun. 



NATURE OF COMETS. Some attempts have been made 

 to define with precision the difference between a star and 

 a comet, and determine by what characteristics a newly 

 discovered star is to be distinguished from one of these 

 wanderers of the firmament. The planets always movo 

 in the same direction ; the plane of their orbits being 

 slightly inclined one to the other, and the eccentricity of 

 these orbits are trifling. Comets on the contrary, for 

 the most part, describe orbits so much elongated that 

 they seem to move in a sort of parabola ; and, in the 

 case of the few with whose movements we are best ac- 

 quainted, the eccentricity of their orbits distinguishes 

 them in a remarkable degree from the planets. Each 



