MICROSCOPIC ACCESSORIES. 



43 



divided is said to be polarized, from a fancied resemblance 

 to the poles of a magnet. The division of the vibrations 

 may be effected (i. ?., the light may be polarized) in vari- 

 ous ways. For the microscope the polarizer is a Nicholas 

 prism, composed of a crystal of Iceland spar, which has 

 been divided and again cemented with Canada balsam, so 

 as to throw one of the doubly refracted rays aside from 

 the field of view (Fig. 22). Such a prism is mounted in 

 a short tube and attached to the under side of the stage. 

 In order to distinguish the effects of polarized light, an 

 analyzer is also needed. This usually consists of another 



FIG. 22. 



FIG. 23. 



Nichol's Pi ism. 



Polarizer and Analyzer. 



similar Nichol's prism, attached either to the eye-piece or 

 just above the objective. The latter position gives a 

 larger field, but the former better definition. Fig. 23 

 shows the polarizer and the analyzer. The polarizer is 

 improved by the addition of a convex lens next the object. 

 Hartnack has also improved the eye-piece analyzer by 

 adding a graduated disk and vernier. 



When the polarizer arid analyzer have been put in place, 

 they should be rotated until their polarizing planes are 

 parallel, and the mirror adjusted so as to give the most 

 intense light. If now the polarizing planes are placed at 

 right angles, by turning one of them 90, the field is ren- 



