ILLUMINATION WITH SUBSTAGE 

 CONDENSER. 



Up to this -point the matter of illumination has been 

 treated in its most simple form as being given with 

 mirror only, but we must now consider the substage 

 condenser, which is a most valuable adjunct to the 

 microscope. While skillfull treatment of the mirror 

 only will go far toward obtaining good results, it will 

 not suffice except in the most simple investigations. 



Purpose of the Condenser. The purpose of 

 the condenser is not only as its name implies, to con- 

 dense light, and thus give an amply illuminated field 

 when the illumination is otherwise insufficient, but is 

 more especially to illuminate the object with a cone of 

 light having an angular aperture equal to that of the 

 objective, which is absolutely unattainable with a mirror 

 only, as well as to provide means for controlling the 

 amount and character of the illumination to suit the 

 various conditions of work. 



Abbe Condenser. The history of the substage 

 condenser is very unique and interesting and shows 

 how, from having been the subject of no end of con- 



