294 Miss Marian Baxter on the Dispersion 



It is interesting to note that at the highest temperatures 

 an absorption band appears near the sodium lines. This -was 

 not identified as one of the known bands of the absorption 

 spectrum of either sodium or potassium. The edges of this 

 band are fairly sharply defined, the wave-length at centre 

 being 5730 approx. 



A second region of general absorption appeared at high 

 temperatures to the left of the blue absorption line. For the 

 highest temperature at which I succeeded in obtaining a 

 photograph, this region extended from line 4199 to line 4529 

 of the iron spectrum. The intensity of light between these 

 lines is too small for measurements to be obtained, and 

 therefore a gap occurs in the curves corresponding to the 

 higher temperatures which widens as the temperature 

 increases. 



If N is the number of fringes parsing any point and \x the 

 refractive index, 



(At — 1) : :N\. 



The dispersion formula of Sellmeier for this case can be 

 written 



and since fju is nearly equal to 1, 



yi6 2 — '1 = 2 (At— 1) approx. 



and 











" x 2 -x 



2 1 -\ 2 

 1 ^ - 



-V 



Let 



X 2 



X 



-V 



be 



represented 



by e 





and 





X 



be 



represented 



by/. 





X 2 



— X2" 





Taking 









Xj = 7-675, 

 X 2 = 4-045, 



X 2 = 



= 58-91 

 = 16-36 



e will then be negative. 



Taking summations over the whole wave-length range the 

 equation becomes 



28 = a£e + a£f. 



