amount
of water escapes through its outlet. According to the
observations of Capt. John McKinney, made at his residence
on the western shore of this Lake, the average seasonal
fluctuation of level is about 0.61 of a meter; but in extreme
seasons it sometimes amounts to 1.37 meters. The Lake of
Geneva, in like manner, is liable to fluctuations of level
amounting to from 1.95 to 2.60 meters, from the melting of the
Alpine snows.

But besides these variations of level due to the variable
quantities of water discharged into them by their affluents,
many lakes of moderate dimensions are liable to rhythmical
oscillations of level of short duration, which are, obviously,
but produced by fluctuations in the supply of water. It is to
this kind of species of variation of level that our attention
will be directed in the sequel.

This interesting phenomenon was first recognized in the Lake
of Geneva; but was subsequently found to be common to all
the Swiss lakes, as well as to those of Scotland. It is,
therefore, a general phenomenon, which may be observed in all
lakes of moderate dimensions. The inhabitants of the shores
of the Lake of Geneva have long designated this rhythmical
oscillation of the level of the water by the term of
_Seiche_; and this designation has been adopted by
scientific writers.

These _Seiches_ were first signalized in the Lake of
Geneva in 1730, by Fatio de Duillier, who ascribed them to the
checking of the flow of the waters of the Rhone on the shoal
near Geneva by the force of the wind at mid-day. Addison
and Jallabert, in 1742, supposed them to be caused by sudden
increments in the discharge of the affluents, due to the
augmentation in the amount of snow melted after mid-day; or
to the sudden increase in the flow of the Arve, checking
the outflow of water by the Rhone. Bertrand supposed that
electrified clouds might locally attract and elevate the
waters of the lake, and thus produce oscillations of level.
H.B. de Saussure, in 1799, attributed the phenomenon to rapid
local variations of atmospheric pressure on different parts
of the lake. J.P.E. Vaucher, in 1802 and 1804, adopted de
Saussure's explanation, and confirmed it by many excellent
observations. He, moreover, established that _Seiches_,
more or less considerable, occur in all t