THE MICROSCOPE 



47 



upward with coarse adjustment until the object is 

 visible. The distance between the end lens of the 

 low power objective and the specimen, when the latter 

 is in focus, should be between 6 and 10 mm. If you 

 find that you have raised the tube more than 10 mm. 

 above the specimen, you have probably missed the 

 focus and should repeat the operation, taking care 

 to focus upward slowly. The specimen will usually 

 be excessively lighted, so one must decrease the dia- 

 phragm opening until the proper degree of illumi- 



A. With plane mirror (correct way). B. With concave mirror (incorrect way). 



FIG. 24. Illumination of Object by Mirror, with Condenser. 



(Bausch & Lomb.) 



nation is secured. Although the specimen is visible 

 and well lighted, the finer details of structure may 

 not be apparent and the fine adjustment should be 

 used to obtain a clearer view. Turn the fine adjust- 

 ment hi each direction not more than five revolutions 

 until best results are obtained. It will usually be 

 necessary to change the fine focus for different parts 

 of the specimen and the student should keep one 

 hand moving this adjustment. As much time is 

 saved by placing the object in the center of the low 



