THE EXPECTED RETURN OF HALLEY'S COMET 549 



was undoubtedly Halley's. Hind contributed a valuable paper 

 to Monthly Notices of the Royal Astronomical Society, vol. x., 

 in which he carried back the history of the comet, with some 

 probability, to the year 12 b.c. He did not compute the 

 perturbations, but based his conclusions on the apparent 

 motions of the comet. 



In the last two years the calculation of the perturbations 

 which the planets have produced on the comet's motion has 

 been carried back to the beginning of Hind's list, and even 

 further; the following list is the result of this examination, 

 and all the returns given in it may be accepted with certainty 

 except the first, which is somewhat doubtful. Hind's list was 

 only sensibly in error in four cases — viz., he gave 



a.d. 608 Nov. instead of 607 March. 



„ 912 April 1 „ „ 912 July 19. 



„ 837 April 6 „ „ 837 Feb. 25. 



„ 1223 July „ „ 1222 Sept. 



It should be added that, owing to the vagueness of the 

 observations, the earlier dates are uncertain by a fortnight or 

 more ; as the observations become more precise the uncertainty 

 diminishes, so that for recent returns it is a very small fraction 

 of a day. 



The list on next page gives the dates of perihelion, the same 

 expressed in Julian days (a very useful way of giving them, 

 since it gets rid of the alterations of the calendar and of 

 the change from b.c. to a.d.), and a few brief notes. Fuller 

 notes on some of the more interesting returns are given at 

 the end. 



It will be seen what an important part the Chinese records 

 have played in the preservation of the earlier apparitions of the 

 comet. Furthermore, while the Western observers generally 

 gave very meagre particulars as to the part of the sky where 

 the comet was seen, the Eastern ones give precise descriptions 

 of its path through the constellations. It is likely that their 

 care in this respect was not altogether disinterested, since they 

 imagined that the terrestrial kingdoms had their counterparts 

 in the sky, and that the comets were ambassadors between 

 them, indicating corresponding relations between the kingdoms 



