THE COMPOUND MICROSCOPE ^^ 



known as the condenser, is fixed below the stage, be- 

 tween the mirror and the object. The condenser, 

 as its name implies, condenses the rays of light re- 

 flected to it by the mirror. It consists of a series 

 of lenses so arranged that they will throw a very 

 powerful cone of light. Provision is made for focus- 

 sing the rays from the condenser on to the object. 



Sometimes, for special forms of illumination, it is 

 necessary to cut off some of the rays ot light passing 

 through the condenser. It may be that we desire 

 to dispense with the outer rays of the cone of light 

 or, when delicate details are being studied, we may 



wish to impede the central rays. In either case 

 diaphragms, popularly called " stops " are used. 

 Our diagrams show A the outer rays of a cone of 

 light cut off and B the central rays similarly 

 treated. 



In old pattern microscopes and in many instru- 

 ments not provided with condensers, the diaphragm 

 used for the purpose of cutting off the outer rays 

 of the cone of light, consists of a blackened circular 

 metal plate, perforated with a number of different 

 sized circular holes. This plate is fixed below the 



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