404 THE BEAUTIES OF NATURE chap. 



by the Sun, the tail, how or why we know 

 not, is repelled. When once driven off, more- 

 over, the attraction of the Comet is not suf- 

 ficient to recall it, and hence perhaps so many 

 Comets have now no tails. 



Donati's Comet, the great Comet of 1858, 

 was first noticed on the 2d June as a faint 

 nebulous spot. For three months it remained 

 quite inconspicuous, and even at the end of 

 August was scarcely visible to the naked eye. 

 In September it grew rapidly, and by the 

 middle of October the tail extended no less 

 than 40 degrees, after which it gradually 

 disappeared. 



Faint as is the light emitted by Comets, 

 it is yet their own, and spectrum analysis has 

 detected the presence in them of carbon, 

 hydrogen, nitrogen, sodium, and probably of 

 iron. 



Comets then remain as wonderful, and 

 almost as mysterious, as ever, but we need no 

 longer regard " a comet as a sign of impend- 

 ing calamity ; we may rather look upon it as 

 an interesting and a beautiful visitor, which 

 comes to please us and to instruct us, but 



