steboard cylinder, five or six centimeters in diameter, and
sixty or seventy centimeters in length, was sometimes employed
for the purpose of excluding the surface reflection and the
disturbances due to the small ripples on the water. When
quietly floating in a small row-boat, one end of this
exploring tube was plunged under the water, and the eye of
the observer at the other extremity received the rays of light
emanating from the deeper portions of the liquid. The light
thus reaching the eye presented essentially the same
variety of tints in the various portions of the Lake as those
which have been previously indicated.

Hence it appears that under various condition--such as depth,
purity, state of sky and color of bottom--the waters of this
Lake manifest nearly all the chromatic tints presented in
the solar spectrum between greenish-yellow and the darkest
ultramarine-blue, bordering upon black-blue.

It is well known that the waters of oceans and seas exhibit
similar gradations of chromatic hues in certain regions.
Navigators have been struck with the variety and richness of
tints presented, in certain portions, by the waters of the
Mediterranean Sea, the Atlantic and Pacific Oceans, and
especially those of the Caribbean Sea. In some regions of the
oceans and seas, the green hues, and particularly those tinged
with yellow, are observed in comparatively deep waters, or, at
least, where the depths are sufficiently great to prevent
the bottom from being visible. But this phenomenon seems to
require the presence of a considerable amount of suspended
matter in the water. In no portion of Lake Tahoe did I observe
any of the green tints, except where the light-colored bottom
was visible. This was, probably, owing to the circumstance
that no considerable quantity of suspended matter existed in
any of the waters observed.

_Rhythmical Variations of Level in Lakes: or
"Seiches."_--As might be expected, the waters of Lake
Tahoe are subject to fluctuations of level, depending upon
the variable supplies furnished by its numerous affluents. In
mid-winter, when these streams are bound in icy fetters, the
level falls; while in the months of May and June, when the
snows of the amphitheater of mountain-slopes are melting most
rapidly, the level of the Lake rises, and a maximum