THE COMET OF 1812 AND 1883. 489 



as well as the comet of 1812, now visible on its first predicted return. 

 It was originally detected on the 20th of July, and was the thirteenth 

 discovered by Pons within ten years. Its appearance at first was that 

 of an irregular nebula without tail or beard, and it was only visible 

 through a telescope. By the 14th of September it was easily seen 

 without optical aid ; its tail was over two degrees in length, and the 

 diameter of its nucleus was five or six seconds. It continued visible 

 till October a period of ten weeks and was consequently well ob- 

 served. Cooper's valuable work on " Cometic Orbits " contains eight 

 sets of elements by different computers. Encke distinctly recognized 

 the elliptic form of the orbit, and the elements which he assigned have 

 been generally preferred. They are as follows : 



Perihelion passage, 1812, Sept., 15-3136, G. M. T. 



Longitude of perihelion 92 18' 46" 



>0 -I I t) It 



Longitude of ascending node 253 1' o 



Inclination 73 5*7' 3" 



Perihelion distance 0-V71 



Eccentricity 0'9545 



Period 70 68 years. 



Motion direct. 



According to Encke, therefore, the next perihelion passage was to 

 have been expected in June, 1883 about three months before the 

 actual discovery of the comet by Mr. W. R. Brooks. A re-discussion 

 of the observations of 1812 had, however, been recently completed by 

 Dr. Schulhof and M. Bossert, whose calculations gave a probable pe- 

 riod about seven months longer than that obtained by Encke. The 

 true period is found to be very nearly a mean between these earlier 

 and later estimates. 



On its present return the comet was first glimpsed on the night 

 of September 1st, by Mr. William R. Brooks, Director of Red House 

 Observatory, Phelps, New York. He was, however, prevented by 

 clouds from verifying his conjecture of the cometary character of the 

 nebulous speck till the evening of the 3d. Its identity with the comet 

 of 1812 was shown on the 18th of September, by the Rev. Mr. Searles, 

 of New York, and independently on the day following by Professor 

 Lewis Boss, of the Dudley Observatory. The latter designated Janu- 

 ary 25, 1884, as the date of perihelion passage. Astronomers of the 

 twentieth century will probably witness its next apparition in the 

 summer of 1955. 



The comet of 1812 is one of a remarkable group whose periods 

 range between sixty-eight and seventy-six years, all of their aphelia 

 being some distance beyond the orbit of Neptune. It seems, how- 

 ever, to be specially related to the fourth comet of 1846. The latter 

 was discovered by De Vico, at Rome, on February 20th, and inde- 

 pendently, by Professor G. P. Bond, February 26th. It remained 

 visible ten weeks, and its elements were calculated by Peirce, Hind, 



