hed _equally_, or by the same absolute
quantity. They must be reduced _proportionately_, instead of equally.
If by the act of reflection the waves of red light are split into
exact halves, then, to preserve the light white, the waves of yellow,
orange, green, and blue, must also be split into exact halves. In
short, the reduction must take place, not by absolutely equal
quantities, but by equal fractional parts. In white light the
preponderance, as regards energy, of the larger over the smaller waves
must always be immense. Were the case otherwise, the visual
correlative, blue, of the smaller waves would have the upper hand in
our sensations.

Not only are the waves of aether reflected by clouds, by solids, and
by liquids, but when they pass from light air to dense, or from dense
air to light, a portion of the wave-motion is always reflected. Now
our atmosphere changes continually in density from top to bottom. It
will help our conceptions if we regard it as made up of a series of
thin concentric layers, or shells of air, each shell being of the same
density throughout, a small and sudden change of density occurring in
passing from shell to shell. Light would be reflected at the limiting
surfaces of all these shells, and their action would be practically
the same as that of the real atmosphere. And now I would ask your
imagination to picture this act of reflection. What must become of
the reflected light? The atmospheric layers turn their convex
surfaces towards 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 fashion from the
aerial layers to the earth, there is indubitable evidence to show that
the light of our firmament is scattered 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 comes to us across
the direction of the solar rays, and even against the direction 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