xxiv INTRODUCTION 



2. Never examine an object with the high power unless it 

 is protected by a cover-glass. Take extreme care never to let 

 the objective touch the cover-glass : and never to touch the 

 face of the objective or allow any dirt to get on it. The face 

 of an objective cannot be cleaned without doing harm to it. 



3. Keep both eyes open when looking through the micro- 

 scope. Also get into the habit of using either eye. 



4. When examining an object, keep one hand on the fine 

 adjustment, and keep screwing it up and down slightly. In 

 this way parts of the objects at different depths are brought 

 into focus, and a much clearer idea of the object is obtained. 



5. With a high power, use a small diaphragm : the amount 

 of light will be somewhat diminished, but the clearness and 

 definition of the object much increased. 



6. See that the body of the microscope slides smoothly in 

 its tube. If it does not, remove it, and clean it by rubbing 

 with a few drops of olive oil. 



7. The object may appear indistinct from dirt in any of 

 the following places, i.e. on the eye-piece, the objective, or the 

 cover-glass. If it be on the cover-glass the dimness varies 

 when the slide is moved ; if on the eye-piece, it varies when 

 this is rotated ; if not on either of these, it must be on or in 

 the objective. 



The eye-piece and the lower surface of the objective may 

 be cleaned with chamois -leather or silk. If the objective 

 is smeared with glycerine, wash it carefully, then dry with a 

 soft handkerchief. Canada balsam, which sometimes gets on 

 the objective, may be removed with a drop of turpentine on a 

 handkerchief. It is, however, safer to leave this to an optician 

 or to the demonstrator, as a very small quantity of turpentine, 

 getting inside the rim which carries the lens, may lead to the 

 separation of the two lower lenses from each other, rendering 

 the objective useless. 



