ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



513 



in. and 13/32 in. working distance, and is then suitable for use with 

 the lower powers. 



Fig. 129. 



New Refractometer with Variable Refractive Angle.*— This in- 

 strument, made by Zeiss and designed by Dr. C. Pulfrich, is intended 

 for the examination of a very highly refractive liquid, which is placed 

 between two glass plates as in a kind of hollow prism, but with the 

 difference that the refractive angle of the prism can be varied at pleasure. 



Fig. 130. 



One of the two glass plates (B in fig. 130) forms the horizontal floor of 

 a glass trough intended for the reception of the liquid ; the other glass 

 plate G takes the form of a slightly conical cylinder several centimetres 

 long with even end-planes. The lower end of this cylinderrdips into 



* Zeitsch. f. Instr., 1899, pp. 335-9 (4 figs.). 



