118 MICROSCOPIC OBJECTS. 



differ both in size and form. Under the microscope, 

 they should have their transparent parts clearly and dis- 

 tinctly separated from the darker portions. This remark 

 holds good for the whole tribe of hairs and mosses, and 

 it is from the sharpness with which the parts are sepa- 

 rated that a correct opinion of the goodness of an in- 

 strument can be obtained. When these hairs are seen by 

 reflected hght, that is, as opaque objects, their appear- 

 ance is altered, the dark solid parts reflecting more light 

 than the transparent portion ; hence they are lighter than 

 the latter. 



'' The diameter of the mouse's hair varies from one two- 

 thousandth to one three-hundredth of an inch ; they do 

 not require a high power to see them. 



" (2.) The hair of the Field Mouse fMus sylvaticusj 

 possesses a structure totally difierent from the former 

 species, and is a good microscopic object. 



" (3.) The hair from the wing of the Bat (Vespertllio 

 miirinusj. — Although this creature is supposed to bear 

 some affinity to the mouse, the structure of the hair of 

 these two animals is entirely different. There are, how- 

 ever, great varieties ; some are spiral, others like a suc- 

 cession of cones, the apex of one being inserted into the 

 base of the following. 



"(4.) The Lycana Argus. — Among the scales on the 

 under side of the wing of this elegant blue Butterfly are 

 some whose conformation is remarkably singular : their 

 general appearance is not unlike a child's battledore with 

 its surface covered with spots. I have not been able 



