09 



COMETS. 



COMETS. 



70 



Biela'i Comet. This comet was discovered on the 27th of February, 

 1826, by Biela, an Austrian officer residing at Josephstadt, in Bohemia. 

 Parabolic elements of its orbit were shortly afterwards calculated, and 

 the results are found to bear a strong resemblance to the elements of 

 comets observed in 1805 and 1772. This circumstance induced 

 Gambart, the director of the observatory of Marseille, and Clausen, 

 assisting astronomer at the observatory of Altona, simultaneously to 

 compute elliptic elements of the comet's orbit. The results obtained 

 by those two astronomers presented a satisfactory agreement with each 

 other, and represented the observed places of the comet much better 

 than the elements originally computed. The time of revolution was 

 found to be nearly 6'6 years. Professor Santini of Padua computed 

 the effects of planetary perturbation for the next return to the peri- 

 helion. By a discussion of the observations made subsequent to the 

 discovery of the body, he found that it passed through the perihelion 

 on the 18th of March, 1826, and that the corresponding time of revo- 

 lution was 2455'170 days. Computing, then, the disturbing forces of 

 the Karth, Jupiter, and Saturn, he found that the effect of their com- 

 bined influence would be to shorten the time of revolution by 10'023 

 days, and that the comet would consequently pass through the peri- 

 helion on the 27th of November, 1832. It is a curious fact, that this 

 comet, a little before its arrival in the perihelion, passes through the 

 descending node of its orbit at only a very short distance from the 

 earth's orbit. Great fears of a collision of the two bodies were 

 consequently entertained, when it was announced as the result of 

 astronomical calculation, that at the instant of the passage of the 

 comet through its descending node on the 29th of October, the earth 

 would be travelling in the same region. However, an exact com- 

 putation of the earth's motion relatively to the comet had the effect of 

 dispelling these apprehensions; for it was found that, although the 

 comet would pass from the north to the south of the ecliptic on the 

 29th of October, the earth would not arrive in the same heliocentric 

 longitude before the 30th of November. 



The comet, on the occasion of its re-appearance, was first perceived 

 on the 23rd of August by the observers of the Collegio Romano at 

 Rome. Its passage through the perihelion took place within a few 

 hours of the time fixed by the calculations of Professor Santini. The 

 next passage of the perihelion took place in 1839, but the circumstances 

 of its motion being unfavourable for observation, the comet passed 

 unperceived. The results of Professor Santini's calculations showed 

 that the next perihelion passage would take place on the llth of 

 February, 1846. On this occasion the comet did not pass unobserved. 

 It wag re-discovered, independently, on the 28th of November by 

 Professor Encke, at Berlin, and Signer De Vico at Rome. During 

 the interval of ita visibility it underwent a singular change, having 

 separated into two distinct fragments which continued to travel together 

 at a distance of 3' or 4' from each other. This singular phenomenon 

 appears to have been first unequivocally observed on the 12th of 

 January, 1846, by Lieut. Maury, of the Observatory of Washington, 

 (U.S.). One of the comets was considerably fainter than the other. 

 Both bodies were seen for the last time on the 16th of April, 

 1846. Professor Plantamour computed the elements of the orbit 

 described by each comet, taking into account the perturbations pro- 

 duced by the Earth, Jupiter, and Mars. The places of the two 

 bodies when computed from these elements, were found to agree 

 very nearly with the observed places. Professor Plantamour de- 

 termined the mutual distances of the two bodies, and obtained the 

 following results : 



Date. Mutual Distance. 



1816 February 10 

 17 



.. * 

 March 3 



.. ,, 1 



21 



140,820 miles. 

 183,530 

 196,641} ,, 

 157,220' 

 155,790 

 154,210 



The comet was again observed on its return to the perihelion in 

 1852. The appearance which it presented on that occasion continued 

 to afford evidence of the disruption which it suffered in 1846, both 

 fragments being still visible. Circumstances do not seem to have been 

 favourable for ita re-discovery at the time of the perihelion passage 

 of 1859. 



Payt?t Cornel. On the 22nd of November, 1843, a comet was dis- 

 covered by M. Faye, at the Royal Observatory, Paris, the observations 

 of which it was found impossible to satisfy by a parabolic orbit. Dr. 

 Goldschmklt wa induced by this circumstance to compute an elliptic 

 orbit for the comet, and obtained results which agreed very well with 

 the observed motion. The time of revolution is 2718 days, or 7'44 

 yean. The comet ha* been re-observed on the occasions of its return 

 to the perihelion in 1851 and 1858. 



Br or ten' i Comet. -On the 26th of February, 1846, M. Brorsen dis- 

 covered at Kiel, in Denmark, a small telescopic comet, which was 

 speedily found to revolve hi an elliptic orbit, the time of revolution 

 being about 6'6 years. It was not observed on the occasion of the 

 pawaee of the perihelion in 1851, but it was found at the next return 

 to the perihelion in 1857. 



VAm*Ct Comet. This comet was discovered by Professor D'Arrest, 

 at Leipsic, on the 27th of June, 1851. It was speedily found to 



revolve in an elliptic 'orbit, the period being about 6-4 years. The 

 circumstances of the next perihelion passage were calculated by M. 

 Villarceau, of the Imperial Observatory, Paris ; and by the aid of an 

 ephemeris, due to that astronomer, the comet was re-discovered at the 

 Cape of Good Hope by Mr. Maclear, on the 5th of Decembe, 1857. The 

 comet continued to be observed till the 18th of January, 1858. During 

 the whole period of its visibility it presented a very faint aspect. 



(2) Cornels which have been found to rerolre in elliptic of 1,'ls, but 

 chick hare not been re-observed since the dlscorery of their period 't>i. 



A considerable number of comets in addition to those contained in 

 the foregoing list, have exhibited traces of a deviation from parabolic 

 motion, and elliptic orbits have in consequence been calculated for 

 them, the results derived from which have been found to satisfy 

 the observations with a greater or less degree of precision. We 

 proceed to notice briefly the results relative to the periodic time 

 which have been obtained for a few of the more interesting of those 

 bodies. 



Comet of 1680. Halley was of opinion that this comet was identical 

 with comets which appeared in the years B.C. 43, A.D. 531, and 1106 ; 

 and he hence inferred a period of 575 years. Professor Eucke, how- 

 ever, has found by an investigation, based upon all the recorded obser- 

 vations, that the most probable value of the periodic time is 8800 years ; 

 but he remarks that in consequence of the large probable errors of the 

 data, the observations of the comet may be tolerably satisfied by an 

 ellipse with a period of 805 years, or even by an hyperbolic orbit. The 

 observations ef Flamsteed and Newton alone indicate a period of 3164 

 years. 



LexdFi Comet. This comet was discovered by Messier in 1770. 

 Astronomers having been unable to satisfy the observations by para- 

 bolic elements, an elliptic orbit was computed by Lexell, who found 

 the periodic time to be somewhat more than five years. The comet 

 was carefully searched for on the occasion of the next two expected 

 returns to the perihelion, but it was not discovered in either instance, 

 nor has any trace of it been ever since obtained. Lexell endeavoured 

 to account for this curious circumstance by remarking that previous 

 to 1770 the comet had always been invisible, but that having passed 

 very close to the planet Jupiter in the year 1767, it was thrown into 

 a new orbit, and rendered riiible ; and that, in 1779, having again 

 approached very near to the same planet, it was thrown again into a 

 new orbit, and thereby rendered invisible. The researches of Lexell 

 were subsequently confirmed by Laplace, but Le Verrier has in recent 

 times called in question some of the data on which they rest. 



Comet of 1811. The orbit of this famous comet has formed the 

 subject of an elaborate investigation by Argelander, who found it to 

 revolve in an ellipse, with a period of 3065 years. This result must 

 be understood, however, as corresponding only to the time of the 

 perihelion passage. Argelander has shown that the disturbing forces 

 of the planets must exercise a very considerable influence on the time 

 of the next perihelion passage. By computing the perturbations up to 

 May, 1827, he found that the time of revolution would be shortened 

 from that cause to the extent of no less than 177 years. 



Comet of 1815. This comet was discovered on the 6th of March, 1 815, 

 by the celebrated astronomer Olbers. Bessel subjected the observa- 

 tions to a thorough discussion, when he found the comet to revolve in 

 an ellipse, with a period of 74 years. Taking into account the effects 

 of planetary perturbation, which he found would accelerate its 

 movement to the extent of two years, he finally ascertained that 

 the comet would again arrive in the perihelion in the month of 

 February, 1887. 



De Pico's Comet. On the 22nd of August, 1844, De Vico discovered 

 at Rome a comet which was found to revolve hi an elliptic orbit, with 

 a period of about five and a half years. It was carefully searched for 

 at the perihelion passages of 1850 and 1855, but in neither instance has 

 it been discovered. 



Peters' Comet. This comet was discovered by Dr. Peters at Naples, 

 in 1846, and was found by him to revolve in an elliptic orbit with a 

 period of 12'85 years. According to this result the comet ought to 

 have returned to the perihelion in the year 1859, but hitherto it has 

 not been found. 



Wiiineektfi Comet. On the 8th of March, 1858, Dr. Winnecke dis- 

 covered a comet at Bonn, which he found to revolve in an elliptic 

 orbit with a period of 5'549 years. He also established its identity 

 with a comet observed in the year 1819. Supposing it to have made 

 seven revolutions since that year, the time of a complete revolution 

 would be 5'541 years, a result agreeing almost exactly with that 

 obtained by a direct investigation of the elliptic elements. 



Donati's Comet. The observations of this famous comet appear to 

 be best satisfied by an elliptic orbit. According to Professor Stampf er 

 of Vienna, the period of revolution is 2141 years. However, until the 

 totality of the observations shall have been subjected to a complete 

 discussion, it will be impossible to arrive at any definitive result on 

 this point. 



Number of Comets. 



It is impossible to form any opinion with respect to the number 

 of comets which are liable to visit our system. Multitudes of those 

 bodies, whether from their faintness or the circumstances of their 

 movements, will doubtless for ever elude observation. Arago gives 



