172 



Mr. J. N. Lockyer. On the Classification [Jan. 10, 



IV. THE STAGE IMMEDIATELY PRECEDING PERIHELION. 

 Manganese Absorption. 



It has been pointed out that in the case of a comet approaching 

 perihelion, manganese is first represented by the radiation of the 

 fluting at 558. As the comet gets nearer to perihelion, if the 

 perihelion distance be sufficiently small, we find the radiation of 

 manganese replaced by absorption. 



The reason that the presence of the strongest manganese fluting at 

 558 has not been previously recorded is, I fancy, that the masking 

 effects of one spectrum on another, to which I referred in the Bakerian 

 Lecture, have not been present in the minds of even those observers 

 who were familiar with low- temperature spectra. 



I have obtained abundant evidence that the masking phenomena 

 manifest themselves in the spectra of comets, but since there is in 

 general so little continuous spectrum to be absorbed (from which we 

 can gather that the meteorites are farther apart in comets at this stage 

 than they are in many stars of Group II), we have chiefly to deal, 

 when discussing absorption, with the masking of the radiating citron 

 fluting of carbon by the absorption of metallic vapours. 



The way in which the manganese absorption shows itself in comets 

 is generally by the obliteration of the red end of the citron fluting, 

 which produces an apparent shifting of the carbon fluting towards the 

 more refrangible part of the spectrum. The way in which this comes 

 about is shown in fig. 5. The manganese absorption masks the 



Hot carbon radiation. 

 Manganese absorption. 

 Integrated result. 

 Comet III, 1868. 



iig. 5. Diagram showing the result of the integration of hot carbon radiation and 

 manganese absorption, compared with Comet III, 1868. 



brightest part of the carbon fluting, leaving a sharp edge at 558. 

 This has been observed in eight comets when not far from perihelion, 

 namely : 



