105 



It might be said here in parenthesis that tl 

 mirror should always be used with the conde 



To Focus Condenser. An excellent plan for 

 focusing the condenser is to do so by means of a 

 low power objective, f to 3 inch, in the microscope 

 tube. After the slide is in contact with the condenser 

 or when not used with immersion and close to it, 

 focus the objective on the object. Now adjust the 

 condenser until the image which it projects of the 

 source of light is coincident with it. In the case of a 

 lamp, the flame will be projected. Daylight offers no 

 tangible image, and while the image of the window- 

 frame is not really quite correct, it is, in most cases, 

 sufficiently close for all practical purposes. 



Intensity of Light. To say what amount of 

 light shall be used is very difficult on account of the 

 variety of specimens which involve different condi- 

 tions. While it is claimed that on stained bacteria 

 the best plan is to use the full volume of illumination 

 and thus differentiate the objects, it is certainly detri- 

 mental to do so on many histological specimens, diat- 

 oms and others, as they would be drowned in light 

 to such an extent as to be in some cases indistinguish- 

 able. The safest plan will be to use the minimum of 

 light and gradually increase until the point for pro- 

 per observation is reached. It will also be a good 

 plan not to use more light than is needed to accom- 

 plish the purpose desired. 



To obtain oblique illumination, reduce the aperture 

 to i inch and gradually bring the opening out of the 



