ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



235 



Frauenhofer's Screw Micrometer.*— This instrument is fitted to a 

 telescope or Microscope of low power, and is mounted on a brass column. 

 It is provided with turning movements so that it can be used vertically 



Fig. 42. 



Fig. 43. 



(fig. 42) and horizontally (fig. 43), and measurements taken in all 

 directions. The micrometer can change places with the shelf, so that 

 the instrument may serve as Microscope with micrometric shelf. The 

 tripod folds up. 



(2) Eye-pieces and Objectives. 



Societe Genevoise : Eye-pieces for Mineralogical and Petrog-ra- 

 phical Microscopes.! — Fig. 44, numbered 2442 in the maker's cata- 

 logue, represents an auxiliary nicol, with divided circle for use above the 

 ocular. Figs. 45, 46, numbered 2485 by the makers, show Babinet's 



* List Phys. and Meek. Instr. Soc. genevoise, 1907, pp. 36-7 (2 figs.), 

 t Catalogue (1907) of the Soc. genevoise pour la construction d'iustrumentsde 

 physique et de niecanique, p. 12. 



R 2 



