THE MICROSCOPE STAND 109 



is reflected, and the reflected light at the time it emerges has 

 travelled a path that is longer than the direct light by the 

 aniount A B. This difficulty was overcome by making a special 

 pair of eyepieces whose focal points were difierent in position, 

 but it limits the use of the instrument to the use of special 

 eyepieces. 



Vi 



Fig. 102.- 



-Diagram showing paths of light through the Beck Binocular 

 Microscope. 



(A) Eyepiece. 



(B) Drawtube. 



(D) Body. 



(E) Coarse focussing adjustment. 

 (V) Prism box knob. 



(9) Sliding prism box. 



(O) Object glass. 



CI) stage. 



(K) Substage condenser. 



(L) Iris diaphragm. 



(M) Substage focussing adjustment. 

 (N) Mirror. 

 (O) Pillar. 

 (P) Base. 

 (x y) Object. 



(ar' y') Image formed by object glass. 

 (.x!" y') Virtual image formed by eyepiece. 

 (z t") Bamsden discs — conjugate images ol 

 back equivalent plane of object 



