440 MICROSCOPY. 
the light is twice refracted and reflected, the loss of light is much 
less than one would expect. With the microscope, the prism is 
placed right above the objective, and the instrument may be used 
in any inclined position. A pair of such prisms might be used 
also for an erecting binocular microscope, of iak tive tae i 
have the same inclination to the stage. i 
Fig. 1 shows the front and profile of the prism. The projection 
of the. front is a square, that of the profile an isosceles triangle. 
The angles at the 
base of the triangle 
are 27°19 for crow 
olass of a refracting 
A 53, mM 
index 1.99, 
Fig. 2 is a view from above. The rays A, B and Cof nga f 
2 are the identical ones, their dotted parts are whe projet a 
the rays inside of the glass, and their course may be rem’. 
followed in the profile, fig. 1, where the upper ray, mer? 
the lower one, and the lower ray, C, as the upper One. : 
As the ray A enters in the perpendicular line above the 
rges as 
lower 
