ZOOLOGY AND BOTANY. MICROSCOPY, ETC. 555 



about vertical and horizontal axes, or two axes perpendicular to each 

 other but inclined to the vertical or horizontal. Provision is thus made 

 for keeping an object in the field of the telescope when it is being 

 employed for astronomical purposes. 



Bausch and Lomb's 1912 Model B H 8.*— This instrument (fig. 94) 

 as will be seen from the illustration, has the horse-shoe foot and the 

 arm is of the handle type. The stage, covered with vulcanized rubber, 

 measures 103 mm. by 101 mm. The substage consists of a mounting 

 for the Abbe condenser and an iris diaphragm which comes into the 



Fig. 94. 



plane of the stage when the screen is turned up as far as possible, 

 allowing the condenser to be used in immersion contact with the objec- 

 tive if desired. When screwed down the substage swings to the left of 

 the optical axis. The outside diameter of the body tube is 35 mm. 

 The fine-adjustment is of the lever type, with two-sized knurled head 

 for slow and rapid movement. 



Bausch and Lomb's Model F F. — The principal feature of this 

 instrument (fig. 1)5) is the handle-arm the curve of which provides con- 



* Bausch & Lomb Optical Co. Catalogue, 1912, pp. 30-31. 

 t Bausch & Lomb Optical Co. Catalogue, 1912, p. 34. 



2 p 2 



