THE MICROSCOPE IN GEOLOGICAL INVESTIGATION. 317 



pendently of the stage, and can be precisely centered by the two milled- 

 heads, c and c'. In the lower (rotating) part of the body, there is a 

 horizontal slit at B for the introduction of laminae of gypsum, quartz, 

 etc., and into the lower end of the ocular tube can be fitted a cone that car- 

 ries the converging lenses necessary to transform the instrument into an 

 Amici microscope, its distance from the objective being regulated by the 

 rack near the top of the eye-tube. 



