160 PROCTOR, ON LIGHT. 
whiteness of substances in a fine state of division, and how 
far that is dependent upon their degree of opacity or trans- 
parency, may be shortly dismissed, for we have already con- 
sidered the action of comminution on bodies of considerable 
transparency, and we have concluded that all substances are 
in some degree transparent. We have only now to repeat that 
reduction to a powder produces subjacent surfaces which re- 
flect some of the light which passes through the first surface ; 
the greater the degree of comminution, the more light is re- 
flected from the subjacent substances. But reducing a substance 
to powder, by converting its surfaces into numberless facets, 
inclined at all conceivable angles to the general plane of re- 
flection, diminishes the amount of light availably reflected 
from the primary surfaces, which will be more clear by con- 
sidering it with the diagram before us. 
In the diagram we have four eyes looking at different 
kinds of surfaces:—No. 1 will receive a certain amount of 
light reflected from the plane surface. No. 2 will receive little 
more than half the quantity ; it is supposed to be looking at 
a grooved surface in which the dentations are flat on the top, 
and separated by indentations of an equal width; half the 
light falls upon the tops of the ridges, and is reflected the 
same as from the plane; the other half falls into the grooves, 
and cannot reach the eye, except after many reflections and 
much loss. No. 3 looks at a serrated surface, in one portion 
