THE MICROSCOPE AND ITS PARTS. 17 



when it learns, as it will, to see minute parts of deli- 

 cate objects which at the start were entirely over- 

 looked, the high-power objective will not be thrown 

 aside, the student will not become disgusted with it as 

 he would become with a high-power French triplet,, 

 but his quickened sight will again catch glimpses of 

 beauty to be examined, and mystery to be unravelled, 

 which are still beyond the power of his best objective, 

 and he will almost unconsciously have advanced an- 

 other step. 



Personally the writer prefers the -|-inch objective to 

 the J, and such a lens need not be expensive to be 

 good (several opticians' "Students' Series" include 

 them), the working distance is not too short, or need 

 not be, and with the two-inch eye-piece it will give a 

 magnifying power of about two hundred and fifty di- 

 ameters. 



"The coarse adjustment" is the expression usually 

 applied to the rapid movement of the body produced 

 by turning the large milled-heads, one of which is on 

 each side of the instrument. It is used in focusing, 

 that is, in obtaining a distinct image of the object when 

 seen through the eye-piece and objective. The image 

 then appears surrounded by a disc of light called the 

 "field of view," or simply "the field." Very few, ex- 

 cept the small, vertical "boys'-microscopes," and some 

 of the cheapest and least desirable American or English 

 stands, are without the coarse adjustment. Occasion- 

 ally a stand will be seen in which this part is replaced 

 by a broad, cloth-lined, or tightly-fitting collar, through 

 which the body slides, the movement being made by 

 hand. This is very unsatisfactory, and such stands 

 should be avoided, if possible^ as, sooner or later, the 



