ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 701 



removing the lower and middle lenses the power is reduced to 200, 

 with a focal distance of 6 mm. and a sensitiveness of 0"008 mm. 

 For the illumination of transparent objects there is a mirror V, a 

 condensing lens on a separate stand being used for opaque ones. 



The centering telescope K has cross-threads (movable by four 



Fig. 126. 



small screws), adjusted exactly in the axis of the goniometer. It 

 moves in a groove in the base-plate in the direction of the axis. 



The method of measuring is briefly as follows : — (1) the edge of 

 the surfaces to be measured is placed parallel to the goniometer- 

 axis by means of the thread in the eye-piece ; on turning the 



Ser. 2.— Vol. III. 3 A 



