11(3 SUMMARY OF CURRENT RESEARCHES RELATING TO 



stand (supra, p. 115). It consists of a wide-angle achromatic condenser 

 with double diaphragms, dark-ground illuminator, and polarizing 



Fig. 1. 



apparatus. The condenser has an angle of 180°, that can be varied 

 at will by the diaphragms. It can be drawn away when not in use 



