160 



on the top of condenser, drop the slide upon the 

 stage, first throwing the clips to one side. With 

 immersion objectives the proper focusing of the 

 condenser becomes a matter of nice distinction to 

 obtain best results and can only be reliably accom- 

 plished by considerable practice and experience. 



To obtain best position use a f objective ; focus upon 

 the object, after the slide has been brought in fluid 

 contact with condenser and tJien adjust condenser 

 until image of flame will fall in the same plane with 

 the object, 



Relation of Aperture of Condenser to Ob- 

 jective. As has been stated the condenser may 

 be the means of doing more harm than good, 

 depending mainly upon the angle of illumination 

 used. Too much illumination decidedly injures 

 definition by obliterating detail. In the study of 

 Bacteria and Micrococci, with which the objectives 

 used are of wide aperture, it is sought to have 

 them stand out boldly in a bright field, which is 

 accomplished by bringing the diaphragm to its 

 full aperture. 



In all dry objectives the aperture of the condenser 

 should be less than that of the objective. 



Little experience is required to judge when the 

 condenser has its proper opening. When correct, 

 the image will stand out sharply defined without 

 any appearance of fogginess and as the aperture is 



