e produced by the action of a given cause having a maximum
amplitude.

_Causes_. The disturbances of hydrostatic equilibrium
which generate _Seiches_ may be produced by a variety of
causes. Among these, the following may be cited: (a) Sudden
local variations of atmospheric pressure on different parts of
the lake. (b) A descending wind, striking the surface of the
lake over a limited area, (c) Thunder-storms, hail-storms, and
water-spouts; and especially when the accompanying winds act
vertically. (d) The fall of a large avalanche, or of a
land-slide into the lake. (e) And lastly, earthquakes.

Observations show that the most frequent and evident of
these causes are variations of atmospheric pressure and local
storms. With regard to earthquake shocks as a cause of such
fluctuations of level, it is a singular and significant fact
that since Forel has established the delicate self-registering
apparatus on the shores of the Lake of Geneva, no less than
twelve earthquake shocks have been experienced in this portion
of Switzerland, and they have had no sensible influence on
these sensitive instruments. In fact, a little consideration
in relation to the character of such shocks renders it highly
improbable that such brief tremors of the earth's crust
could have been any agency in the generation of rhythmical
oscillations of the whole mass of water in the lake. Indeed,
it is very questionable whether any earthquake waves are ever
produced in the ocean, except when the sea-bottom undergoes a
permanent vertical displacement.

_Lake Tahoe_. From inquiries made of the inhabitants of
the shores of Lake Tahoe, I was not able to discover that any
rhythmical oscillations of the level of its waters have ever
been noticed. Some residents declared that they had observed
sudden fluctuations of level, which, from their suddenness,
they were disposed to ascribe to disturbances of the bottom of
the Lake due to volcanic agencies, although they were
unable to coordinate such oscillations with any earthquake
manifestations on the adjacent shores.

It is evident, however, that until arrangements are
consummated for recording systematic observations on the
variations of the level of this Lake, we cannot expect
that its _Seiches_ will be detected. Of course,
self-registering gauges wo