4 ' Fred J. Bates 



86 sin^ (i7.4'+.4')+94 sin^ (i3.3'4-.4')-^99 sin^ (10.2'+. 4') + 

 103 sin2(7.i'+.4') + io4.5 sin'^ (3'+. 4') = 



86 sin^ (3'— .4')+94 sin^ (7. i'— .4')+ 99 sin- (10.2'— .4') + 



103 sin^ (13.3— .4) + io;.5sin- (17.4— .4) (VII) 



Hence, with a transparent substance, giving a rotation of about 

 4.77° for 566 /A/A, the normal to the principal axis of the analyzing 

 nicol, for the light source considered, will be rotated from the 

 median position C//" through an angle, 80.=.^' (=.006°) to a posi- 

 tion 0//\ 



In a similar manner we now change the coefficients of equation 

 (VII) to correspond to the luminosity curve resulting from passing 

 sunlight through a fuchsin solution (see Table I) and we get 

 approximately 



86X21.7 sin^ (17.8'— 4.i')+94Xio.5 sin^ (13.7'— 4. i') + 



99X5 sin- (10.6'— 4.1') + 103X2. 3 sin^ (7.5'— 4.1') + 



104.5X1 sin2(3.4'— 4.1') = 



86X2i.7sin2(2.6'+4.i')+94Xio.5 sin'- (6.7'+4.i') + 



99X5 sin^ (9-8'+4-i') + i03X2.3 sin-^ (i2.9'+4. i') + 



io|.5Xi sin^ (i7'+4.i'). 



Hence the normal moves through an angle of 4.1' from OH' to 

 OH". Thus it becomes evident that the change in the luminosity 

 curve of the light reaching the eye, due to the absorption of the 

 fuchsin solution, gives with the half-shade system an apparent 

 rotation of the plane of polarization of approximately 4.1' 

 (0.065°) under the conditions assumed above. Under the same 

 conditions the magnitude of this effect observed experimentally 

 was 0.055°. 



Errors due to the change in the luminosity curve similar to 

 the one just discussed also enter in a proportionately greater 

 degree into Wiedemann's^ and allied methods of measuring the 

 rotation of plane polarized light in and near an absorption band. 



iG. Wiedemann, Pogo-. Anjt. 82, p. 215. 1851. 



