ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



361 



correction depends, as with aplanatics, on the inner surface of the 

 cemented double lens, of which one lens B is made from a negative 

 flint glass lens, and the other is a positive me- 

 niscus C of weakly refractive crown glass; the jr 

 resultant focal length of the double leus being j^ 

 negative. 



(3) Illuminating- and other Apparatus. 



Winkel's Drawing Apparatus for Weak 

 Magnifications.* — A horse-shoe foot supports a 

 pillar 8 which carries, by means of the screw A, 

 the object-table T and the mirror E (fig. 77). 

 The screw B serves as a clamp. The large per- 

 foration of the object-table renders the instru- Fig. 76. 

 ment applicable to large preparations, and the 



carrier T permits the insertion of a disc of ground glass for uniform 

 illumination of the field. The optical portion is placed at the upper 



Fig. 77. 



* Zimmermann, Das Mikroskop, pp. 138, 9; and Zeitscbr. wies. Mikr., x. (1893) 

 p. 289. 



