THE MICROSCOPE AND ITS PARTS. 21 



to have the image as distinct as possible. If in doubt 

 as to the focus, after obtaining what seems to be a 

 moderately good appearance, give the fine adjustment a 

 turn or two one way or the other, noticing whether the 

 image becomes sharper in outline and clearer in its gen- 

 eral aspect, or whether it grows cloudy and indistinct. 

 If the last, the focus has not been improved, and was 

 probably correct at first. A very little experience will 

 make the beginner an expert in this important matter. 



The stage, on all but the largest and most expensive 

 instruments, is a square or circular piece of thin metal, 

 with a large central circular opening for the passage of 

 the light from the mirror. Sometimes the metal stage 

 has a glass plate made to slide over it easily. This is a 

 convenience and a desirable luxury, but it is by no 

 means necessary. The strip of glass that bears the ob- 

 ject to be examined can just as readily be slipped about 

 under the objective by the fingers directly, as it can be 

 if supported on this movable glass stage. These finger 

 movements require a little practice, but the student will 

 so soon become accustomed to them that he will change 

 the position of the object without consciously thinking 

 of it, and his touch will become so delicate that he will 

 be able, with the slightest pressure, to move the object 

 for a distance so small that it would be invisible to the 

 naked eye. All this is rather awkward at first, because 

 the object must be moved while the eye is looking 

 through the microscope ; and, in addition, if it is to be 

 pushed to what appears to be the left-hand side of the 



