m (probably not exceeding three or four per
cent.), it is evident that solar light must penetrate to
vastly greater depths in these pellucid waters.

Moreover, it is quite certain that if the experiments
in relation to the depths corresponding to the limit of
visibility of the submerged white disk had been executed in
winter instead of summer, much larger numbers would have been
obtained. For it is now well ascertained, by means of the
researches of Dr. F.A. Forel of Lausanne, that the waters of
Alpine lakes are decidedly more transparent in winter than in
summer. Indeed, it is reasonable that when the affluents of
such lakes are locked in the icy fetters of winter, much less
suspended matter is carried into them than in summer, when all
the sub-glacial streams are in active operation.

Professor Le Conte goes into this subject (as he later does into the
subject of the color of Lake Tahoe) somewhat exhaustively in a purely
scientific manner and in too great length for the purposes of this
chapter, hence the scientific or curious reader is referred to the
original articles for further information and discussion.

_Color of the Waters of Lake Tahoe_. One of the most
striking features of this charming mountain Lake is the
beautiful hues presented by its pellucid waters. On a calm,
clear, sunny day, wherever the depth is not less than from
fifty to sixty meters, to an observer floating above its
surface, the water assumes various shades of blue; from a
brilliant Cyan blue (greenish-blue) to the most magnificent
ultramarine blue or deep indigo blue. The shades of blue
increasing in darkness in the order of the colors of the
solar spectrum, are as follows: Cyan-blue (greenish blue),
Prussian-blue, Cobalt-blue, genuine ultramarine-blue, and
artificial ultramarine-blue (violet blue). While traversing
one portion of the Lake in a steamer, a lady endowed with a
remarkable natural appreciation and discrimination of shades
of color declared that the exact tint of the water at this
point was "Marie-Louise blue."

The waters of this Lake exhibit the most brilliant blueness
in the deep portions, which are remote from the fouling
influences of the sediment-bearing affluents, and the washings
of the shores. On a bright and calm day, when viewed in the
distance, it had the ultramarine hue; but when