4 ELEMENTS OF APPLIED MICROSCOPY. 
column proceeds in a direction parallel to that which it 
originally pursued. 
It will be noted that in passing into the region offering 
greater resistance the marching column takes up a direc- 
tion more nearly at right angles to the boundary of that 
region; in other words, it is deflected toward a line drawn 
normally, or at right angles, to that boundary (l,). So 
by hg 
—- 
b @ 
Fic. 2.—ILLUSTRATION OF REFRACTION. (After Hager-Mez.) 
when a ray of light passes from a less dense to a more 
dense medium it is always refracted toward the normal, 
while in passing from a more dense to a less dense medium 
it is bent away from the normal. 
4. Refraction in the Convex Lens.—A ray of light 
passing through a piece of glass with parallel sides will 
simply be shifted laterally, as in our illustration of the 
marching column. In passing through a prism, how- 
ever, a resultant bending ensues as shown in Fig. 3. 
