426 FRAGMENTS OF SCIENCE. 
become of the reflected light? The atmospheric layers 
turn their convex surfaces toward the sun; they are so 
many convex mirrors of feeble power; and you will 
immediately perceive that the light regularly reflected from 
these surfaces cannot reach the earth at all, but is dispersed 
in space. Light thus reflected cannot, therefore, be the 
light of the sky. 
But, though the sun's light is not reflected in this fash- 
ion from the aerial layers to the earth, there is indubitable 
evidence to show that the light of our firmament is scat- 
tered light. Proofs of the most cogent description could 
be here adduced; but we need only consider that we receive 
light at the same time from all parts of the hemisphere of 
heaven. The light of the firmament conies to us across 
the direction of the solar rays, and even against the direc- 
tion of the solar rays; and this lateral and opposing rush 
of wave-motion can only be due to the rebound of the 
waves from the air itself, or from something suspended in 
the air. It is also evident that, unlike the action of clouds, 
the solar light is not reflected by the sky in the proportions 
which produce white. The sky is blue, which indicates an 
excess of the shorter waves. In accounting for the color 
of the sky, the first question suggested by analogy would 
undoubtedly be, Is not the air blue? The blueness of the 
air has, in fact, been given as a solution of the blueness of 
the sky. But how, if the air be blue, can the light of sun- 
rise and sunset, which travels through vast distances of air, 
be yellow, orange, or even red? The passage of white solar 
light through a blue medium could by no possibility redden 
the light. The hypothesis of a blue air is therefore 
untenable. In fact the agent, whatever it is, which sends 
us the light of the sky, exercises in so doing a dichroitic 
action. The light reflected is blue, the light transmitted 
is orange or red. A marked distinction is thus exhibited 
between the matter of the sky, and that of an ordinary 
cloud, which exercises no such dichroitic action. 
By the scientific use of the imagination we may hope to 
penetrate this mystery. The cloud takes no note of size 
on the part of the waves of ether, but reflects them all 
alike. It exercises no selective action. Now the cause of 
this may be that the cloud particles are so large, in com- 
parison with the waves of ether, as to reflect them all 
indifferently. A broad cliff reflects an Atlantic roller as 
