236 
8UMMA11Y OF CURRENT RESEARCHES RELATING TO 
of crystals in media having approximately the same refractive index as 
the mean refractive index of the crystal is shown in fig. 32. 
The rotating pin carrying the crystal projects into the cylindrical 
vessel containing the immersion liquid. The pin is steadied by the 
spring H, and the glass apparatus is firmly held to the circular base- 
plate by the clamp K. 
Fig. 88. Fig. 3 k 
Fig. 35. 
Fig. 36. 
In fig. 33 is shown a more complete apparatus, in which two rotations 
at right angles can be given to the crystal. For this apparatus the 
Microscope must be in the horixontal position. The divided circle M 
is rotated by the head P and is fixed by the screw R. The movable 
axis carries the divided circle K and the object-holder 0. 
