

1889.] of the various Species of Heavenly Bodies. 201 



agrees almost exactly with the blue hand of hot carhon, and if the 

 two other bands be shifted by equal amounts, so that the first one 

 coincides with hot carbon 517, and the second consequently with 

 manganese 558, \ve have indications of manganese added to carbon 

 radiation ; the description of the band, however, is insufficient to 

 enable us to say whether the manganese was radiating or absorbing. 



Huggiris gives flutings at positions which, when reduced, give 464, 

 508, and 544, as the wave-lengths. The wave-lengths of the two less 

 refrangible ones are apparently shortened, as if they were shifted 

 towards the blue. It is probable, however, that manganese was indi- 

 cated by the observations of Huggins, for if we shift the band at 

 508 to 517, the 544 band becomes 553, which is not far removed from 

 the manganese fluting. The drawing given by Huggins shows this as 

 a somewhat narrow band, fading away in both directions, which 

 would seem to show that there was manganese radiation added to 

 carbon radiation, as I have previously explained. This being so, 

 since Muggins's observations were made when the comet was further 

 from perihelion than at the time of Secchi's observations, the dis- 

 cussion of the sequence of changes in other cometaTy spectra suggests 

 that in Secchi's observations we had to deal with the absorption of 

 manganese. 



In a note on the spectrum of Brorsen's Comet at the next return 

 (1879), Professor Young* refers to Huggins's observation. He states 

 that " the only special interest in this (Professor Young's) observa- 

 tion lies in the fact that in 1868 Mr. Huggins obtained a somewhat 

 different result for the same comet." He further goes on to say : " 1 

 am entirely at a loss to explain Mr. Huggins's result. It can hardly 

 be that the comet has really changed its spectrum in the meanwhile, 

 and a careful reading of his account (' Boy. Soc. Proc.,' vol. 16, 

 p. 388) gives no light as to how an error could have crept into his 

 work ; on the other hand, every precaution would seem to have been 

 taken. However this may be, I am quite positive as to the accuracy 

 of my present result that the middle band of the spectrum of this 

 comet now coincides sensibly (to a one-prism spectroscope) with the 

 green band in the hydrocarbon spectrum." 



I have now shown that the spectrum of a comet is by no means a 

 constant, but depends upon the distance of the comet from perihelion 

 passage. The spectrum is, therefore, not necessarily the same at two 

 different returns, as Professor Young supposes, although it may be 

 the same at equal distances from perihelion. 



It is impossible, however, to explain Huggins's observation of 

 Brorsen's Comet without assuming a shift, which is probably instru- 

 mental. In the face of this difficulty, I venture to suggest the above 

 as the probable explanation of the spectrum of this comet. 



* 'Araer. Journ.,' vol. 17, May, 1879. 



