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THE SKY OF THE ALPS. 271

These points were further elucidated by the deportment
of the selenite plate, with which the readers of the fore-
going discourse are already acquainted; On some of the
sunny days of August the haze in the valley of the Rhone,
as looked at from the Bel Alp, was very remarkable. Tow-
ward evening the sky above the mountains opposite to my
place of observation yielded a series of the most splendidly-
colored iris-rings; but on lowering the selenite until it had
the darkness of the pines at the opposite side of the Rhone
valley, instead of the darkness of space as a background,
the colors were not much diminished in brilliancy. I should
estimate the distance across the valley, as the crow flies, to
the opposite mOuntains, at nine miles; so that a body of
air nine miles thick can, under favorable circumstances,
produce chromatic effects of polarization almost as vivid as'
those produced by the sky itself.

Again : the light of a landscape, as of most other things,
consists of two parts: the one part comes purely from
superficial reflection, and this light is always of the same
color as that which falls upon the landscape; the other
part comes to us from a certain depth within the objects
which compose the landscape, and it is this portion of the
total light which gives these objects their distinctive
colors. The white light of the sun enters all substances to
a certain depth, and is partially ejected by internal reflec-
tion; each distinct substance absorbing and reflecting the
light in accordance with the laws of its own molecular con-
stitution. Thus the solar light is sifted by the landscape,
which appears in such colors and variations of color as,
after the sifting process, reach the observer’s eye. Thus
the bright green of grass, or the darker color proper to the
pine, never comes to us alone, but is always mingled with
an amount of really foreign light derived from superficial
reflection. A certain hard brilliancy is conferred upon the
woods and meadows by this superficially-reflected light.

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