334 



THE CHEMISTRY OF THE SUN. 



[CHAP. 



important, much thicker, and much darker than the first, so 

 that here is an absolute inversion in the intensity of the lines. 

 I appeal to the photograph because it is perfectly impartial ; 

 it has no view, no anxiety therefore to intensify one particular 

 part of it at the expense of the other, and it is referred to 

 as the exemplar of many similar reversals which we see 

 whenever such observations are made. 



One word here on the probable origin of these triplets. If 

 one molecular grouping alone were in question, their relative 

 intensity should always be preserved, however much the 

 absolute intensity of the compound system might vary ; but if 

 it is a question of two molecules, we might expect that, in some 



s 



<N CO 



FIG. 109. Anomalous reversals (iron). 



of the regions open to our observation, we should get evidence 

 of cases in which the relative intensity is reversed or the two 

 intensities are assimilated. What might happen does happen ; 

 the intensity of the two triplets in the spark photograph is as we 

 have seen reversed in the spectrum of the sun. The lines barely 

 visible in the spark photograph are among the most prominent 

 in the solar spectrum, and the triplet which is strong in that 

 photograph is represented by Fraunhofer lines not half so thick. 

 While the hypothesis that the iron lines in the region I have 

 indicated are produced by the vibration of one molecule does 

 not include all the facts, the hypothesis that the vibrations are 

 produced by at least three distinct molecules I think does include 

 them. There are other facts in another line of work. In 



