294 AQUATIC MICROSCOPY FOR BEGINNERS. 



ful and skilful preliminary preparation of the ma- 

 terials. The coal must be sliced and ground down 

 until it becomes transparent, 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 

 microscopical examination. The field of even a low- 

 power objective is much smaller, and consequently in- 

 cludes less of the object than the beginner would 

 imagine. Make the experiment by placing a piece of 

 hair a quarter of an inch long under the one-inch ob- 

 jective. 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 appears to be a long distance before 

 the end is brought into view. With the one-iifth inch 

 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 remember that the microscope is for the study of 

 small things. In opaque objects, however, only the 

 surface can be examined — an important and often 

 beautiful part — -but in transparent substances the in- 

 ternal structure can be seen. 



The following is a short list of common objects of 

 interest to the beginner, or, indeed to any one. They 

 are all accessible in the writer's locality; it is hoped 

 that they are equally accessible to the reader. The 

 list is intended only as a start, or a hint as to what 



