the Existence of Carbon in the Sun, 313 



remarkable similarity in character, running with a slight 

 convexity toward one axis. 



In the first fluting at wave-length 3883*7 within the limit 

 of ten wave-lengths, over 28 of the spaces between the fine 

 bright lines of the flutings coincide with dark lines im- 

 mediately in juxtaposition in the solar spectrum. When we 

 consider that the progressive arrangement of these lines is 

 exactly the same both in the spectrum of carbon and that of 

 the sun, we cannot believe that this coincidence is the result 

 of chance. On examining the spectrum of carbon in the 

 region near H still further, a remarkable number of coinci- 

 dences of the spaces between the bright lines of the carbon 

 spectrum with dark lines in the solar spectrum will be ob- 

 served. We are led, therefore, to conclude that the fluted 

 spectrum of carbon is an example of the reversal of the lines 

 of a vapour in its own vapour. Fluted spectra occur at com- 

 paratively low temperatures. When carbon is ignited, we 

 have at first a continuous spectrum. When the temperature 

 increases and the carbon is volatilized, fluted spectra occur, 

 which consist of interruptions of the continuous spectrum by 

 fine line reversals occurring in harmonic order. The same 

 phenomenon can be observed in the spectrum of iron lines : 

 through the centre of an iron line, when a sufficient amount 

 of iron vapour surrounds the Voltaic arc in which iron is 

 volatilized, reversal lines are always seen. Now if the iron 

 lines were arranged in regular order, the reversals would 

 also be in like regular order, and would coincide with similar 

 reversals in the solar spectrum. Assuming the conditions at 

 the sun's surface to be the same as those we have in the 

 Voltaic arc when carbon is volatilized, the character of the 

 carbon spectrum should exactly agree with the character of 

 the solar spectrum juxtaposed. This is found to be true to a 

 remarkable degree in comparing portions of the solar spectrum 

 with portions of the fluted spectrum of carbon beginning at 

 wave-length 3883'7. 



Our hypothesis leads us to conclude, that, at the point of 

 the sun's atmosphere where carbon is volatilized, so as to pro- 

 duce the peculiar arrangement of reversals observed, the 

 temperature of the sun approximates to that of the Voltaic 

 arc. 



Phil Mag. S. 5. Vol. 24. No. 149. Oct. 1887* 



