MICROSCOPIC ILLUSTRATIONS. 257 



be found prejudicial. I think, moreover, that when the 

 construction of an instrument does not admit of the 

 position of the flame of a taper behind the stage, this is, 

 perhaps, the next best way of bringing out the lined 

 objects ; but the taste of mankind in such matters varies 

 incessantly ; every man may be said to see best in his own 

 microscope, &c., and in his own way too, be it what it may. 



14. Single and compound magnifiers, as they exhibit 

 the real object, instead of an image of it, do not require 

 so exact an illumination as engiscopes, and are therefore 

 more easily managed by the inexpert. An engiscope is 

 always very fastidious and ticklish as to its illumination, 

 no error in which can be committed without seriously 

 injuring its performance. Thus, whatever illumination 

 imll suit an engiscope, will be sure to suit simple micro- 

 scopes and doublets ; but what will suit the latter pretty 

 well, will by no means accord with the former. 



15. Opaque objects sometimes require an illumination 

 by means of cups, and sometimes only the natural light 

 of the atmosphere, or of a small wax taper, or rushlight, 

 placed before the stage, as near as may be to the object. 

 With the latter species of illumination the lines on the 

 scales of beetles and butterflies are, perhaps, best brought 

 out ; sometimes, however, a condensation, by means of a 

 lens, is more effective. They can never be seen well with 

 cups, which give an intense direct light; this, however, 

 exhibits flies' feet, and other opaque objects of the same 

 nature, with the highest effect. 



16. The verification of the real nature, form, and con- 

 struction of a vast variety of opaque objects, which elude 

 the sense of touch by their extreme minuteness, can only 

 be made out by an attentive study of their appearances 



