434 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



lein, and Verick have adopted the graduated disk. " There is no 

 doubt," say Nageli and Schwendener,* " that such contrivances are 

 convenient for certain observations (for instance, on circular polari- 

 zation) ; but in most cases it is, at any rate, more important, with 

 crossed Nicols and immovable plates of selenite, to bring the object 

 by means of a rotating plate to the different positions with regard to 

 the planes of polarization of the Nicols, and thus be enabled to deter- 

 mine the angles." 



Apparatus for Rotating Polarizing Objects.! — C. Nageli and 

 S. Schwendener recommend as " practical and fully satisfactory " the 



Fig. 84. 



apparatus (to lie on the stage) shown in fig. 83, for obtaining 

 rotation round a horizontal axis. 



* 'Dae Mikroskop,' 2ncl ed. 1877, Engl, transl. (in the press), pp. 323-7. 

 t Ibid., pp. 326-7 (2 figs.) 



