298 



DR. L. N. G. FILON ON THE 



To simplify the calculation, we may suppose that in the initial state of things 

 Q = 0, so that K = 0, p. = /AQ. As a matter of fact Q cannot be 0, but the assumption 

 that K = 0, p. = /AO is good enough to give the characteristics of the phenomenon 

 sufficiently well for our purpose. 



We have then 



In all the above d/dT! denotes rate of divergence with regard to T of a quantity 

 for the two oppositely polarized rays. Thus 



= C, 



= value of C if there were no absorption band. 



Accordingly, 



i -(x y /x) 2 } ^ {[i - 



+ a >/x>} -i 



gives the deviation produced in the stress-optical coefficient by the absorption band. 

 Calling this SO, we have 



^obs. ' \x\. = C + SC : C. 



4500 



5000 



5500 



TNTH-METf?ES. 



Fig. 10. Diagram showing curve of residuals from straight line for glass 3453. 



Thus the deviation X obs . X^. which is given by fig. 10 is X8C/C. 



X, /^o, C are all comparatively slowly varying : the factor which causes the 

 oscillation is 



x'r. - ..... (25). 



This factor starts with the value when X = 0, decreases to a negative minimum 

 X//a(2Xp+a) when X* = X//(X, + a), and then increases to a positive maximum 

 Xya(2Xp-a) when X 2 = xy(X p -a). It then decreases down to 1 when X = oo . 



