250 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



The revolving eye-piece is also particularly well adapted to use as a 

 micrometer ocular ; for when the eye-lens is turned aside a micrometer 

 scale may be inserted, resting upon the diaphragm of the eye-piece 

 Once adjusted in this way, the micrometer values are the same for all 

 the eye-lenses of the combination. 



Fig. 47. 



Fig. 48. 



Ehrlich's Eye-piece. — This ocular (fig. 49), made by Herr Leitz, is 

 intended to facilitate the estimation of the relative numhers of red and 

 white blood-corpuscles in dry preparations. It is provided with a 

 diaphragm having a square opening, the size of which is regulated by 

 a small lever. 



Fig. 49. 



Leitz' Achromatic and Apochromatic Objective?.— Leitz' objectives, 

 both achromats and apochromats, are manufactured out of Jena glass. 

 The difficulty at one time experienced from the deterioration of this 

 kind of glass, thereby prejudicing microscopists against it, is overcome 

 by using only glass whose durability has been thoroughly well tested. 



