156 HISTOEY OF ASTKONOMY. 



ing to the major axis at that epoch being 308.784 

 years. 



Hence it appears that there is an uncertainty of two 

 years (between August 1858 and August 1860) in the 

 time of the next arrival at perihelion, according as the 

 elements of Dr. Halley or those of Mr. Hind are em- 

 ployed. 



It is an important circumstance as bearing on the 

 question of identity of the comets of 1264 and 1556, 

 that about 289 years before the former epoch, or A.D. 

 975, a comet of great apparent magnitude was visible, 

 which may possibly have been the same. It exhibited a 

 tail 40 in length. Assuming the elements obtained by 

 Mr. Hind for the comet of 1556, and that the perihelion 

 passage took place early in August 975, it is found that 

 the observed track may be very closely represented. 



It is, therefore, inferred that the next perihelion pas- 

 sage of the comet of 1264 will take place within two 

 years of August 1858 ; nearer than this it does not ap- 

 pear possible to approximate in the present state of our 

 knowledge. 



