he Swiss lakes; and
that they take place at all seasons of the year, and at all
times of the day; but, in general, more frequently in spring
and autumn. As regards the cause of the phenomenon, Vaucher
shows how rapid local alterations of atmospheric pressure
would produce oscillations in the level of the lake, and
compares them to the vibrations of a liquid in a recurved tube
or siphon. Finally, Arago maintained that _Seiches_ may
arise from various causes, and traced the analogy between them
and certain remarkable oscillations
of the sea, including those arising from earthquakes.

But physical science is indebted to Professor F.A. Forel, of
Lausanne, for the most complete and exhaustive investigation
in relation to the phenomena of _Seiches_. This
accomplished physicist began his researches in 1869, and has
continued them up to the present time. He has been able to
demonstrate that these rhythmical oscillations occur in nearly
all the Swiss Lakes (he studied the phenomena in nine of
them), and that they follow in all cases the same general
laws. Those of the Lake of Geneva have received the most
elaborate and prolonged investigation. In March, 1876, Forel
established a self-registering tide-gauge (_limni-metre
enregistreur_) on the northern shore of this lake, at
Morges; and, with the cooeperation of P. Plantamour, another
one was installed in June, 1877, at Secheron, near the city
of Geneva, at the southern extremity. Since these dates,
these two instruments have, respectively, been registering
oscillations of the level of the water of the Lake of Geneva;
and they are so sensitive as to indicate the waves generated
by a steamer navigating the lake at a distance of ten or
fifteen kilometers.

From a most searching investigation of all the phenomena
presented by the _Seiches_ in the Swiss Lakes, Forel
deduces the conclusion that they are really movements of
steady uninodal oscillations (balanced undulations), in which
the whole mass of water in the lake rhythmically swings
from shore to shore. And, moreover, he shows that the water
oscillates according to the two principal dimensions of the
lake; thus, giving rise to longitudinal _Seiches_
and transverse _Seiches_. They occur in series of
tautochronous oscillations of decreasing amplitude; the first
wav