ea
beneath it--or the sparkling of the windows of the houses on the
shore.

Previously, at page 10, in calling the molecules of transparent
atmospheric 'absolutely' unreflective of light, I mean, in like
manner, unreflective from their _surfaces_. Their blue color seen
against a dark ground is indeed a kind of reflection, but one of
which I do not understand the nature. It is seen most simply in
wood smoke, blue against trees, brown against clear light; but in
both cases the color is communicated to (or left in) the
_transmitted_ rays.

So also the green of the sky (p. 13) is said to be given by
transmitted light, yellow rays passing through blue air: much yet
remains to be known respecting translucent colors of this kind;
only let them always be clearly distinguished in our minds from the
firmly possessed color of opaque substances, like grass or
malachite.

[Footnote A: In speaking, at p. 11 of the first lecture, of the
limits of depth in the rose-color cast on snow, I ought to have
noted the greater strength of the tint possible under the light of
the tropics. The following passage, in Mr. Cunningham's 'Natural
History of the Strait of Magellan,' is to me of the greatest
interest, because of the beautiful effect described as seen on the
occasion of his visit to "the small town of Santa Rosa," (near
Valparaiso.) "The day, though clear, had not been sunny, so that,
although the snowy heights of the Andes had been distinctly visible
throughout the greater part of our journey, they had not been
illuminated by the rays of the sun. But now, as we turned the
corner of a street, the chain of the Cordillera suddenly burst on
our gaze in such a blaze of splendor that it almost seemed as if
the windows of heaven had been opened for a moment, permitting a
flood of _crimson_ light to stream forth upon the snow. The sight
was so unexpected, and so transcendently magnificent, that a
breathless silence fell upon us for a few moments, while even the
driver stopped his horses. This deep red glow lasted for three or
four minutes, and then rapidly faded into that lovely rosy hue so
characteristic of snow at sunset among the Alps."]]

[Footnote 15: Diffraction.--Since these passages were written, I
have been led, in conversation with a scientific friend, to doubt
my statement that the colored portions of the lighted clouds were
brighter than the white ones. He was convinced that the resolution
of the rays would diminish their pow