l8 AQUATIC MICROSCOPY FOR BEGINNERS. 



body is sure to be suddenly pushed too far down, the 

 objective then coming in contact with the object: an 

 accident to be always guarded against with the great- 

 est care, as the objective, or the object, or both, may 

 be injured. If the object is destroyed it may possibly 

 be replaced, but a scratched or broken objective can 

 be remedied only by buying a new one. Of course, 

 the microscope-body may, by a careless student, be 

 forced againsttheobject by the use of the milled heads, 

 and equally, of course, a man may fill his stomach with 

 gravel-stones or powdered 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 ob- 

 ject on the stage, when the risk is so great. 



The only proper way to use the coarse adjustment is 

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

 ined 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 ob- 

 jective almost touches the object, the observer care- 

 fully watching that they do not come in contact. 

 Then place the eye at the eye-piece, and nothing will 

 be visible except 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 object is focused. It makes no differ- 

 ence whether the distance between the object and the 

 front lens, when focused, is two inches or the one- 

 hundredth part of one inch, always rack the objective 

 down while you are looking a/ it, and focus, upward 

 while you are looking through it. This is the single 

 rule that must never be forgotten. It has been said 



