370 PERIODS OF COMETS. SECT. XXXV. 



of the two comets were separated by about 150,000 miles, and 

 they travelled together with their tails parallel, and an arch of 

 light over their heads. Till that time Biela's comet never had 

 been seen with a tail. The new head was dull at first, but in- 

 creased in size and brightness till it surpassed its companion in 

 both ; besides, it had a bright flashing diamond-like point in its 

 centre gradually it resumed its dull appearance, and its period 

 was computed to be eight days longer than that of the original 

 head. They had separated to a greater distance from one 

 another in 1853, but were still travelling together, one having 

 become smaller than the other. 



A comet discovered by M. Brorsen of Kiel, on the 26th of 

 February, 1846, came, on the 20th of April following, nearly as 

 close to Jupiter as his fourth satellite, when Jupiter's attraction 

 must have been ten times greater than that of the sun ; so there 

 is every reason to believe that the comet's orbit will be as much 

 altered as that of Lexel's ; and another discovered by Padre de 

 Vico at Rome, on the 22nd of August, will, in all probability, be 

 as much disturbed by the same cause. One of the comets found 

 by that astronomer has a period which varies, according to 

 different computations, from 55 to 99 years ; it certainly has 

 an elliptical orbit. That discovered at Naples by Mr. Peters 

 revolves about the sun in 16 years ; but Gibers' s comet of 

 1815 must go nearly the same distance into space with Halley's, 

 since its period is 74 years. Two discovered by M. Brorsen have 

 periods, one of 500 and the other of 28 years ; but of the latter 

 there is some uncertainty. 



The comet which appeared in ] 596 and 1845 has a period of 

 249 years ; and should M. Argelander's computation be accurate, 

 the orbit which has hitherto been assigned to the great comet of 

 1811 must be erroneous, since he has ascertained its period to 

 be 3066 years. 



The great comet of 1264, which had a tail that extended over 

 100 of t'ne celestial vault, was observed and recorded by the 

 Chinese, and was ascertained to be the same that had appeared 

 in 1556, and of whose motions observations were taken at 

 Vienna in the reign of the Emperor Charles V., but it was then 

 less brilliant. In consequence of the discovery of the original 

 observations of the comet of 1556, by Fabricius at Vienna, and 

 by Heller at Nuremburg, Mr. Hind was induced to compute its 



