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white. The sky is blue, which indicates a deficiency on part
of the larger waves. In accounting for the color of the sky,
the first question suggested by the analogy would undoubt-
edly 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 reason, basing itself on observation, asks in reply, How,
if the air be blue, can the light of sunrise 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 hy-
pothesis 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 anordinary cloud, which exercises no such di-
chroitic action.

By the force of imagination and reason combined we
may penetrate this mystery also. 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 size of the waves of ether as to reflect them
all indifl'erently. A broad cliff reflects an Atlantic roller as
easily as a ripple produced by a sea-bird’s wing; and in the
presence of large reflecting surfaces, the existing differences
of magnitude among the waves of ether may disappear.
But supposing the reflecting particles, instead of being very
large, to be very small, in comparison with the size of the
waves. In this case, instead of the Whole wave being
fronted and in great part thrown back, a small portion only
is shivered off. The great mass of the wave passes over
such a particle Without reflection. Scatter, then, a handful
of such minute foreign particles in our atmosphere, and set
imagination to watch their action upon the solar waves.

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