The Microscope Unpacked. 13 



ling at each edge with saw-like teeth. Now take 

 away the bull's-eye lens, place the lamp somewhere 

 near the mirror, and move the latter about till you 

 see the light gleaming brightly upward through the 

 blade of grass. You prepare to look at it, but per- 

 haps are dazzled by the lamplight. If the mirror has 

 two sides, one will be concave, the other plane, and 

 the latter will perhaps suit best with a low power ; or 

 you may moderate the glare from the concave side 

 by turning the " diaphragm- plate " (see p. 16), or by 

 placing a piece of tracing paper under the object. 

 When all is rightly arranged, you will see the grass, 

 a rich green fabric still, but altered. The long trans- 

 parent beads have disappeared ; the plain green lines 

 are now the brightest part of the object, in conse- 

 quence of their being the thinnest. The central rib 

 is nearly black, from its real thickness. The saws at 

 the edge stand out vividly on the bright back-ground, 

 and the whole blade shows a sort of cellular struc- 

 ture, which you would like to see made still larger. 

 If you have a second eye-glass, you may substitute 

 it for the one already in use, and thus gain a higher 

 power, but in many cases you will not find this so 

 satisfactory a method as that of changing the object- 

 glass, while the eye-glass remains undisturbed. 

 Should the object-glass now applied be one of some- 

 what high power, you will find that, alter the screws 

 as you will, you cannot get the whole of the blade of 

 grass sharp and distinct ; that is caused by its want of 

 flatness, and is often an indication that you are em- 

 ploying an unsuitably high magnifier ; if, however, 



