COMETS. 131 



Clerke, " a golden yellow planetary disc, wrapt 

 in dense nebulosity, shone out while the June 

 twilight in these latitudes was still in its first 

 strength." On the same evening the Earth and 

 the Moon passed through the tail of the great 

 comet. The vast majority of people never knew 

 that such a phenomenon had taken place, and 

 even the astronomers only noticed a singular 

 phosphorescence in the sky a proof of the 

 extreme tenuity of comets. 



The first application of the spectroscope to 

 the light of comets was made by Donati in 1864. 

 The spectrum was found to consist of three bright 

 bands, but Donati was unable to identify them. 

 However, his observation gave the death-blow 

 to the theory that comets shone by reflected 

 light alone, for it implied the existence of 

 glowing gas in them. On the appearance in 

 1868 of the periodic comet discovered by 

 Friedrich August Theodor Winnecke (1835-1897), 

 the spectrum was examined by Huggins, who 

 identified the bright bands with the spectrum of 

 hydrocarbon. This was confirmed in regard to 

 Coggia's comet of 1874 by Huggins himself, and 

 also Bredikhine and Vogel. The hydrocarbon 

 spectrum is characteristic of comets, and has been 

 recognised in all those spectroscopically studied. 



The time had now come for a more complete 



