THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



AL OF SCIENCE. 



SEP 19 1921 



O '^' [SIXTH SERIES.] 



SEPTEMBER 1921. 



XXXVII. Dispersion of Light by Potassium Vapour. By 

 Marian Baxter, Assistant Lecturer in Physics, Bedford 

 College, London*. 



[Plate XL] 



The Effect of Temperature on the Relative Values of the 

 Constants of the Sellmeier Formula. 



THE following investigation was originally undertaken 

 in 1913 with the late Dr. P. V. Bevan, who, in a 

 paper on Dispersion in Vapours of the Alkali Metals f, had 

 raised the question of the effect of temperature on the 

 relative values of the constants a x a 2 in the formula 



A 2 "\ 2 



/*«-! = 



x 2 -V \ s — \ s 



Definite experimental evidence on this point would seem 

 to be important, as having some bearing on the nature of 

 the systems which give rise to spectral lines. It was 

 pointed out in the paper mentioned above that an increase 

 in the ratio aija 2 might be expected if the absorption of the 

 different lines were due to different specialized atoms as 



* Communicated bv Prof. A. W. Porter, F.R.S, 

 t Proc. Roy. Soc. A, vol. lxxxv. (1911). 



Phil. May. S. 6. Vol. 42. No. 249. Sept. 1921. X 



