276 MICEOSCOPY FOR BEGINNERS. 



above the stage. To see the sugar crystals, however, or 

 the structure of coal, demands some careful and skil- 

 ful preliminary preparation of the materials. The coal 

 must be sliced and ground down until it becomes trans- 

 parent, or at least translucent, an operation that needs 

 an expert to accomplish. Sugar crystals can be seen by 

 any one, as the reader will presently learn. 



The smaller the object the better it usually is for mi- 

 croscopic examination. The field of even a low-power 

 objective is much smaller, and consequently includes 

 less of the object than the beginner would imagine. 

 Try the experiment by placing a piece of hair a quarter 

 of an inch long under the one-inch objective. You will 

 not be able to see both ends of the hair in the field at 

 the same time. The stage must be moved for what ap- 

 pears to be a long distance before the end is brought 

 into view. With the one-fifth objective the field is still 

 smaller, and the higher the power the smaller the field. 



The object should also be as thin as possible, so that 

 the light may pass through it, unless it is to be viewed 

 as an opaque object, with the light thrown on it from 

 the mirror above the stage. In that case the thickness 

 makes but little difference, if the beginner will remem- 

 ber that the microscope is for the study of small things. 

 In opaque objects, however, only the surface can be ex- 

 amined an important and often a beautiful part but 

 in transparent substances the internal structure can be 

 seen. 



The following is a short list of common objects of in- 



