The Condenser c is carried in the lower substage 

 ring mounted on a lateral axis by which it may be 

 swung to the left, out of the optical axis. It has a 

 centering adjustment operated by the milled heads n n 

 by which its axis can be made to correspond with 

 that of the instrument with the greatest facility. 



Fig. 51c. Complete Substage. Top view, with condenser and lower iris 

 diaphragm swung out of optical axis. 



The Lower Iris Diaphragm d is mounted 

 on the plate o attached to a lateral axis by which it can 

 be swung to the right out of the path of light frcm the 

 mirror. It has a lateral motion by the rack and pinion r b 

 on the plate o and rotates on its own axis so that when 

 oblique illumination with the condenser is desired a 

 small aperture of the diaphragm may be brought the 

 proper distance from the optical axis and rotated to 

 bring it opposite to the direction from which the light 



158 



