For histological and other dense objects the apparent 

 aperture should be equal to about one-half the opening 

 of back lens in objective. 



With dry objectives the aperture of the condenser 

 should always be less than that of the objective, 



Oblique Light with Condenser. Oblique light 

 may be obtained by setting the mirror alone in such a 

 position that the light reflected from it shall enter the 

 condenser only at one side, leaving the balance of it 

 unused. This, however, is only advisable when the 

 condenser mounting has no other provision for obtaining 

 oblique light. In the mountings having such provision 

 oblique illumination may be obtained by two methods : 



/. Focus objective; reduce 

 the apparent aperture to that 

 of the rear lens of the objective, 

 swing the plate o, Fig. 51 a, 

 carrying the lateral adjust- 

 ment around so that the pinion 

 button is at the front. Turn 

 the pinion button so that the 

 opening will move from the 

 center to the periphery of the 

 condenser, Fig. 54. 

 II. Proceed as above with this difference: Remove 

 eyepiece and view the bright circle of light as it passes 

 from the center to the periphery of the rear lens. 



Fig. 54. Illuminating object by 

 oblique light with condenser. 



164 



