Errors in Methods of Measuring Rotary Polarization 3 



tween the direction of vibration in the nicols of the polarizing 

 system, is obtained by direct measurement when there is no rota- 

 tion of the light. ^ We thus find 



Also for 



That is 



(ai+a„)=20.4'. 



X in fi/A 



566 

 580 



Rotation 



4-77" 

 4-53'' 



(oi— a„ ) = I4-4' 

 O-n =3'- 



Considering now the luminosity curve, S, of the sun^ and the 

 transmission curve of a fuchsin solution,^ F, in fig. 2, and taking 

 w=5 we have 



TABLE I 



where X=573 /^/t^ for example is taken as the mean intensity of the 

 interval from 571.5 /"•;". to 574.5 /a/a. 



By successive approximation (VI) is solved with sufficient accu- 

 racy, and we obtain by considering only the luminosity curve: 



^The analyzer was set for blackness of one-half of the field arid then 

 rotated to a similar position for the other half. The angle of rotation is 

 (ai4-a„). 



^Marscart, Optique, I, p. 104, pi. I. 



^This curve was kindly determined for the writer by Professor B. E* 

 Moore. The concentration, parts by weight, was 0.000024. 



257 



