ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
467 
(A) A small reflecting prism (p in fig. 80) for quickly finding tlie 
zero-point of tlie telescope. This is placed between the eye-piece and 
cross-wires, and is illuminated by a source of light opposite the opening 
u to the right of the observer. 
(B) A diaphragm with elliptic aperture placed before the objective 
to cut off all disturbing light from the facets of the upper face of the 
prism. 
Universal Apparatus for the Investigation of Thin Slices in 
Liquids.*- — Prof. C. Klein describes the universal apparatus which he 
D 
has devised for the optical examination of sections of minerals and rock-; 
in liquids of high refraction. 
Fig. 82. 
The apparatus (figs. 81 and 82) is sufficiently large to allow of the 
examination of ordinary rock-sections. A rectangular metal plate P, 
* SB. K. Preuss. Akad. AViss., 1895, pp. 1151-9. 
