CHAPTER XX. 



SOME TEST EXPERIMENTS. ABSORPTION PHENOMENA. 



WE are now in a position to test the new hypothesis by a 

 detailed reference to those solar phenomena and connected 

 laboratory experiments which can bear upon it. But on the 

 festina lente principle, which I have so far adopted, I propose in 

 the first instance to state the results of several new modes of 

 experimental investigation which I tried with the view of 

 throwing light if possible upon the question of molecular 

 complexity raised in 1873. 



I have shown in chap. xiv. when dealing with the difficulties 

 connected with the old view, the growing importance of the 

 question of multiple spectra, and how, as the work went on, the 

 number of observers who ascribed them to impurities got less 

 and less. Some of the new methods have to do with the question 

 of multiple spectra, and a brief reference to them will show that 

 their results are almost entirely in favour of the new view, and 

 that the progress of spectrum analysis increases the possible 

 number of molecular groupings. We began with line spectra 

 and fluted spectra as the maximum of variation ; we end with 

 line and fluted spectra both of complex origin, and new orders 

 of spectra altogether, determined by absorption or radiation of 

 a continuous sort in one or other part of the spectrum. 



These points may be discussed seriatim, and I propose to take 

 the last first. 



T 



