294 THE CHEMISTRY OF THE SUN. [CHAP. 



as its brightest, a yellow line, which is also of marked import- 

 ance in the solar spectrum. The flame spectra of lithium and 

 potassium give us, as their brightest, lines in the red which have 

 not any representatives among the Fraunhofer lines, although 

 other lines seen with higher temperatures are present. 



Whence arises this marked difference of behaviour ? From 

 the similarity of the flame spectrum to that of the sun in one 

 case, and from the dissimilarity in the other, we may imagine 

 that in the former case that of sodium we are dealing with a 

 body easily broken up, while lithium and potassium are more 

 resistant ; in other words, in the case of sodium, and dealing 

 only with lines recognised generally as sodium lines, the flame 

 has done the work of dissociation as completely as the sun it- 

 self. It is easy to test this point by the method now under con- 

 sideration, for if this reasoning be correct (1) the chief lines and 

 flutings of sodium should be seen in the flame itself, and (2) 

 the spark should pass through the vapour after complete 

 volatilisation has been effected without any visible effect. 



Observation and experiment have largely confirmed these 

 predictions. Using two prisms of 60 and a high-power eyepiece 

 to enfeeble the continuous spectrum of the densest vapour pro- 

 duced at a high temperature, the green lines, the flutings recorded 

 by Roscoe and Schuster, and another coarser system of flutings, 

 _so far as I know not yet described, are beautifully seen. I say 

 largely, and not completely, because the double red line and the 

 lines in the blue have not yet been seen in the flame, either 

 with one, two, or four prisms of 60, though the lines are seen 

 during volatilisation if a spark be passed through the flame. 

 Subsequent inquiry may perhaps show that this is due to the 

 sharp boundary of the heated region, and to the fact that the 

 lines in question represent the vibrations of molecular groupings 

 more complex than those which give us the yellow and green 

 lines. The visibility of the green lines, which are short, in the 

 flame, taken in connection with the fact that they have been 



