400 SPECIAL RESULTS IN THE URANOLOGICAL 



and colour, and of the emanations from the head, which, 

 bending back, form the tail ( 654 ), following in my descrip- 

 tion the observations of Heinsius (1744), Bessel, Struve, 

 and Sir John Herschel. In recent times, besides the mag- 

 nificent comet of 1843 ( 655 ), which was seen by Bo wring at 

 Chihuahua (N.W. America) as a small white cloud, from 

 nine in the morning to sunset, and by Amici at Parma, in 

 full noonday, at 1 23' east of the Sun ( 656 ), the 1st comet 

 of 1847, discovered by Hind in the neighbourhood of Ca- 

 pella, was visible in London on the day of its perihelion, 

 when very near the Sun. 



Tor the further elucidation of what has been said above, 

 respecting the remarks of the Chinese astronomers on the 

 occasion of their observation of the comet of March 837, 

 during the dynasty of Thang, I will here introduce a trans- 

 lation from the Ma-tuan-lin, of the statement of the law 

 followed in the direction of the tails of comets : " In 

 general, in a comet east of the Sun, the tail, reckoning from 

 the nucleus, is directed to the east ; but if the comet appears 

 to the west of the Sun, the tail is turned towards the west." 

 (657^ Fracastoro and Apianus say more definitely, and still 

 more correctly, that " a line in the direction of the axis of 

 the tail, prolonged through the head of the comet, strikes 

 the centre of the Sun." The words used by Seneca (Nat. 

 Qusest. vii. 20), " the tails of comets flee from the Sun's 

 rays," are also descriptive of their character in this respect. 

 Among the planets and comets yet known to us, while the 

 proportion of the shortest to the longest period of revolution, 

 dependent on the length of the semi-major axis, is in planets 

 as 1 : 683, in comets it is as 1 : 2670. These ratios are 

 derived from comparing Mercury, having a period of revo- 



