of Light by P.otassium Vapour. 299 



range (4090-5200) is used. This latter range is restricted 

 so as to include photograph S, in which there is a small 

 intensity of light near the sodium lines. In the first two 

 photographs the slope of the fringes is slight, and for photo- 

 graph 1 the numerical results indicate no more than the 



Fur. 2. 





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4040 60 



Wave length. 



order of the ratio «]/a 2 . It was found that for these two 

 photographs the values of the constants obtained from the 

 shorter wave-length range gave calculated values of n which 

 differed considerably from the observed values, though for 

 the other photographs the agreement was good, as soon from 

 trie diagram. 



40 



