er, and in _thinking_ over the
matter, I am disposed to agree with him, although my impression at
the time has been always that the diffracted colors rose out of the
white, as a rainbow does out of the gray. But whatever the facts
may be, in this respect the statement in the text of the
impossibility of representing diffracted color in painting is
equally true. It may be that the resolved hues are darker than the
white, as colored panes in a window are darker than the colorless
glass, but all are alike in a key which no artifice of painting can
approach.

For the rest, the phenomena of diffraction are not yet arranged
systematically enough to be usefully discussed; some of them
involving the resolution of the light, and others merely its
intensification. My attention was first drawn to them near St.
Laurent, on the Jura mountains, by the vivid reflection, (so it
seemed), of the image of the sun from a particular point of a cloud
in the west, after the sun itself was beneath the horizon: but in
this image there were no prismatic colors, neither is the
constantly seen metamorphosis of pine forests into silver filigree
on ridges behind which the sun is rising or setting, accompanied
with any prismatic hue; the trees become luminous, but not
iridescent: on the other hand, in his great account of his ascent
of Mont Blanc with Mr. Huxley, Professor Tyndall thus describes the
sun's remarkable behavior on that occasion:--"As we attained the
brow which forms the entrance to the Grand Plateau, he _hung his
disk upon a spike of rock_ to our left, and, surrounded by a glory
of interference spectra of the most gorgeous colors, blazed down
upon us." ('Glaciers of the Alps,' p. 76.)

Nothing irritates me more, myself, than having the color of my own
descriptions of phenomena in anywise attributed by the reader to
accidental states either of my mind or body;--but I cannot, for
once, forbear at least the innocent question to Professor Tyndall,
whether the extreme beauty of these 'interference spectra' may not
have been partly owing to the extreme _sobriety_ of the observer?
no refreshment, it appears, having been attainable the night before
at the Grands Mulets, except the beverage diluted with dirty snow,
of which I have elsewhere quoted the Professor's pensive
report,--"my memory of that tea is not pleasant."]

[Footnote 16: 'Either stationary or slow in motion, reflecting
unresolved light.'

The rate of motion is of course not