F. E. Wright — Bi-quartz Wedge Plate. 



393 



Moreover, if the wedge is inserted horizontally and at such a 

 point that its effect on the plane of polarization of transmitted 

 light is precisely zero, a straight, black, vertical band appears 

 in each half of the field similar to the bands in the Babinet 

 compensator (fig. 2). By means of this band, the true position 



FiCx. 1. 



w 



R 



Fig. 1. Proposed arrangement of parts in polarimeter, using bi-quartz 

 wedge plate as sensitive device. P, polarizer : T, sugar solution tube ; W, 

 bi-quartz wedge ; C, degree circle of analyzer ; O, Eamsden ocular ; A, 

 analyzer. Although the bi-quartz plate wedge may or may not be attached 

 to the revolving circle mechanism, it seems preferable that its carriage 

 should remain in one plane. The ocular may be used either in front or 

 back of the analyzer A, and may be a single acromatic lens in place of the 

 positive ocular. Observations can also be made without the aid of the ocular 

 and thus an increase of light intensity gained. 



of the analyzer can be found with great accuracy, for the set- 

 ting is thus made to depend upon the exact alignment of two 

 black bands and the photometric principle of comparing two 

 dimly lighted fields is for the most part eliminated. 



Another advantage of this system lies in the fact that the 

 boundary lines between the halves of the wedge can be made 

 of knife-edge sharpness without the disturbing division line in 

 the center of the field produced by the total reflection and con- 



