Comet ary Light. 283 



floor. From such a division Bessel was led to the idea of 

 a heterogeneous composition in 1807; and in 1858, though 

 the pale thin narrow beam which preceded the grand flowing 

 train of cc the Donati" was totally missed in England, and 

 found few spectators anywhere, yet its existence is too well 

 established to admit of doubt, and inevitably leads to a similar 

 conclusion. 



Diversity of colour, too, points strongly in the same direc- 

 tion. This has always been a recognized peculiarity among 

 comets; not only in ancient and less accurate, but in our 

 own careful, modern days. Virgil's beautifully . picturesque 

 description — ■ 



" liquids si quando nocte cometce 

 Sanguinei lugubre rubent," 



would lead us to suppose that since the epithets would hardly 

 apply to the majority of cases, he must have witnessed some 

 such portent of an unusually deep and fearful hue ; and the 

 Chinese record of Ma-tuon-lin, compiled in the thirteenth 

 century, vague as it is in some respects, yet careful and precise 

 in this, speaks not only of red, but white, blue, yellow, and 

 violet comets. In our own times, no one who recollects the 

 different aspect of the two great comets of 1858 and 1861 could 

 doubt of the fact ; while, as far as I can remember, the orange 

 tint even of the last was exceeded by the very fiery and angry 

 aspect of that of 1854, the sabre-like precursor of the Russian 

 war. Even between the different parts of the same comet a 

 curious difference of tint has been noticed. In 1811 ?§. re- 

 marked the very peculiar greenish or bluish-green colour of 

 the head, while its central point had a pale ruddy tinge ; and 

 in 1858 the very feeble and wide-spread nebulosity surrounding 

 the head was thought by Winn e eke and Fearnley to be of a 

 light-blue colour, while the head and tail were yellow. Here 

 the reflected light, which was probably concerned, seems to 

 speak sufficiently of diversity of material ; but with the native 

 light of the nucleus the case is still more evident, for spectrum- 

 analysis teaches us that in all such instances a difference of 

 colour, at least at corresponding temperatures, indicates the 

 presence of a different element. We have no reason therefore 

 for surprise at the contrast between the two spectra, one 

 figured by Donati, the other described by Huggins. 



In one respect, however, the comparison is not fully satis- 

 factory. It does not appear how Donates spectrum was 

 obtained. Huggins, on the contrary, examined separately the 

 nucleus and the coma, and hence possibly succeeded in obtain- 

 ing more decisive evidence of its gaseous nature than can be 

 deduced from Donates figure. One great fact comes out in 



