1-18 



Pr. W. Huggins. On the 



[June 15, 



district. During this period, there have been some disturbances of a 

 volcanic nature, as the limestone is cut by dykes of basalt, and of com- 

 pact trachytes which, however, differ considerably from the purplish 

 rhyolites already mentioned. As there is a possibility of this island 

 having remained above water from a very remote antiquity, the in- 

 vestigation of its flora and fauna will possess a peculiar interest. 



XV. " On the Photographic Spectrum of Comet (Wells) I. 1S82." 

 By William Huggins. D.C.L., LL.D.. F.R.S. Received 

 June 15, 1882. 



On the evening of Wednesday. May 31. I obtained a photograph of 

 the spectrum of this comet with an exposure of one hour and a 

 quarter. A spectrum of a Ursa? Majoris was taken through the other 

 half of the slit, on the plate, for comparison. 



The photograph shows a strong continuous spectrum extending 

 from about F to a little beyond H. In this continuous spectrum I am 

 not able to distinguish the Fraunhofer lines. In this comet therefore, 

 at this time, the original light giving a continuous spectrum must 

 have been much stronger relatively to the sunlight reflected than was 

 the case in the comet of last year. It should be stated that the greater 

 faintness of the present comet made it necessary to use a more open 

 slit, which would cause the Fraunhofer lines to be less distinct ; but 

 the lines OK H. and K are to be clearly seen in the star's spectrum 

 taken under the same conditions. 



Eye observations by several observers on the visible spectrum of 

 the comet had already shown that this comet for the first time since 

 spectrum analysis was applied to the light of these bodies in 1S64, 

 gives a spectrum which diners essentially from the hydrocarbon type 

 to which all the comets previously examined spectroscopically (^about 

 twenty ^ belong. 



In the visible spectrum bright lines, presumably of the vapour of 

 sodium, and some other bright lines and bright groups of lines have 

 been seen. The hydrocarbon bands in this part of the spectrum have 

 been suspected to be present by some observers. 



The photographic spectrum differs greatly from that of the comet 

 of last year.* I am not able to see the cyanogen group in the ultra- 

 violet beginning at wave-length 3SS8. nor are the other two groups 

 between G and h and between 7; and H to be detected. 



The continuous spectrum which extends from below F to a little 

 distance beyond H. contains at least five brighter space-, which are 

 doubtless groups of bright lines, though it is not possible in the pho- 



* u Proe. Eoy. Soc," vol. 33, p. 1. 



