20 AQUATIC MICROSCOPY FOR BEGINNERS. 



made for the better by a few delicate touches of the 

 fine adjustment can be appreciated only when seen. 

 Always try 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 become sharper in outline 

 and clearer in its general aspect, or whether it grows 

 cloudy and indistinct. If the "last, the focus has not 

 been improved, and was probably correct at first. A 

 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 a 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 object 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 

 the act, 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 



