394 



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



sequent depolarization of light waves on the edge of the small 

 prism of the Lippich system. The edges of the two halves of 

 the bi-quartz plate are first polished and then cemented vyith 

 Canada balsam, which has practically the same refractive index 

 (1-540 compared with 1-544), so that no appreciable total reflec- 

 tion with the accompanying depolarization occurs. This is the 

 same result which was successfully attained by Brace,* who 



Fig. 2. 



expended an extraordinary amount of care aiid ingenuity in an 

 effort to free the field from this disturbing dividing line ; but 

 his instrument is not of such mechanical construction as to lend 

 itself readily to ordinary laboratory use. 



Still another favorable feature of the wedge plate scheme 

 for adjusting the sensibility of a polarimeter is the position of 

 the accumulator or magnifying lens of short focal length, which 

 is necessarily of greater light intensity than the telescopic 

 ocular usually used to view the polarizing system. 



Fig. 3. 



w 



O 



& 



Fig. 3. Proposed arrangement of parts in quartz compensating polariscope 

 using bi-quartz plate wedge as sensitive device. P. polarizer : T, sugar 

 solution tube ; Q, quartz compensating system ; W, bi-quartz wedge plate ; 

 O, ocular ; A, analyzer. As in fig. 1, the ocular may be used either in 

 front of or back of the analyzer ; a single achromatic lens may be substituted 

 for the Ramsden ocular, or the magnifying lenses may be done away with 

 altogether. 



If a quartz compensating system be used and a white light 

 source, the arrangement outlined in fig. 3 might prove advan- 

 tageous. The quartz compensating system has been adopted on 



* D. B. Brace, Phil. Mag. (6), v, 161, 1903. 



