DESCRIPTION OF THE ACHROMATIC MICROSCOPE. 97 



coal ; jet ; the fructification of ferns and mosses ; fossil 

 shells; seeds; small insects, or parts of large ones; molus- 

 cans, or entomostraceans ; the circulation in the frog, &c. 

 the eye-piece, A 9 is best adapted. 



Again, for examining the details of any of the above 

 objects, the eye-piece, B, should be substituted ; as also 

 for observing the colours of crystals illuminated by pola- 

 rized light ; the pollen of flowers ; the dissections of 

 insects ; the vascular and cellular tissues of plants ; ani- 

 malcules; Haver's canals in sections of recent, and 

 the corpuscules, &c. in fossil bones ; the cyclosis in 

 plants; the formation of shell; the moveable fluids in 

 quartz and topaz ; the organic remains in thin slices of 

 flint, &c. ; the serrated lamina of the crystalline lenses 

 of the eyes of fishes and birds, &c. &c. 



And lastly, when it is requisite to investigate either the 

 minutiae of opaque objects, or the minute structures of 

 delicate tissues, active molecules, polygastric infusoria, 

 and the raphides in the milky juice of plants, &c. the 

 eye-piece, C, comes into use ; it being oftentimes incon- 

 venient, when a higher power is needful, to obtain it by 

 means of a deeper object-glass, which occasions a fresh 

 arrangement to be made of the illumination and focus. 



It must, however, always be borne in mind, that the 

 more powerful the eye-piece is, the more will the imper- 

 fections in the object-glass become apparent, because 

 they will be the more dilated. Hence we should observe, 

 that less confidence ought to be placed in the observa- 

 tions made under a powerful eye-piece, than when the 



