THE MICROSCOPE AND ITS PARTS. 19 



man may fill his stomach with gravel-stones or powder- 

 ed glass ; but no sane man will so maltreat that organ, 

 and no sane microscopist will so maltreat his objective 

 as to drive it against the object on the stage when the 

 risk is so great. 



The only proper way to use the coarse adjustment is 

 to always focus upward. When the object to be ex- 

 amined has been placed on the stage, and the light from 

 the mirror is properly arranged, the microscope body, 

 with the eye-piece and objective, is racked downward by 

 means of the milled heads until the front of the objec- 

 tive almost touches the object, the observer carefully 

 watching that they do not come in contact. Then place 

 the eye at the eye-piece, and nothing will be visible ex- 

 cept the brightly illuminated field of view ; but, while 

 looking into the microscope, slowly raise the body until 

 the image appears sharp and clear, in other words until 

 the objective is focussed. It makes no difference wheth- 

 er the distance between the front lens, when focussed, 

 and the object is two inches or the one-hundredth part 

 of one inch, always rack the objective down while you 

 are looking at it, and focus upward while you are look- 

 ing through it. This is the single rule that must never 

 be forgotten. It has been said in a joking way, "that 

 nothing will throw a microscopist into a chill more 

 quickly than to see a friend look into his microscope 

 and focus down with the coarse adjustment." Yet men 

 who ought to know better have been seen to do this 

 reprehensible thing. 



