The Portland daily press. [volume] (Portland, Me.) 1862-1921, 1897-09-08
VARYING LAKE LEVELS.
Inquiries as to the Causes of the So-Called
Tidal Waves.
(From the Cleveland Plain Dealer. }

(From the Cleveland Plain Dealer.)
which are popularity, but enormously,
styled "tidal waves" have attracted at
tention and caused speculation among
scientists and laymen. The late Col.
Charles Whittlesey was much interested
in the subject and published mono
graph, in which was collected all the in
formation attainable concerning the
PECULIAR oscillations of level observed on
Lake Erie, which had no apparent con-
nection with prevailing wind currents.
A steady wind from one direction 'spiles
up the water at the lower or upper end
of the lake, and materially changes the
level for time, but the "tidal waves, ~
or ''seiehe," as they are scientifically
termed, are of different character from
this "piled up water, and cannot be ex-
planned in the same manner On a still
day, when the surface of the lake is
CLASSY limits. tranquility, "a huge wave. sud-
denly forces its way up the shore, fol-
lowed at intervals by one or more of less
volume. Sometimes the sudden rise OF
water is but a few inches; at others, if
the reports of excited observers can be
trusted. it is many feet, and runs up the
creeks with destructive force. When the
tidal waves" have receded the lake is,
for while at least, as smooth and SEEM
ingly pulseless as before, but 1t is the
general belief that the oscillations presage
a storm.
At the British Association meeting on
Monday Mr.. E. Napirer Denison of the
Toronto University read paper on ''The
Great Lakes as a Sensitive Barometer, -
in which an attempt. was made to explain
the causes of these oscillations of lake
surface. Mr.. Denison's observations were
taken IN the shallower part of Lake On
tario, fronting Toronto, under conditions
strongly resembling those at the Lake
Erie ports where the .stidal waves, have
been most noticed. The records show
that the longitudinal and transverse
"seiche" movements are very marked
preceding and during storms primarily
due to differences of atmospheric pres
sure over the extremities of the lake, but
greatly augmented when the gale strikes
the water surface. The mean time inter
val of longitudinal "seiche" is four hours
and forty nine minutes; the transverse,
forty-dve minutes. There is a marked
agreement between the time intervals of
the. smaller lake undC1atiOns and those
found upon the corresponding sensitive
Paragraph traces, both showing a pre-.
dominance of twenty minute intervals.
Mr.. Denison explains the smaller lake
undulations as due to atmospheric waves,
which are set up along the boundary sur
faces of different air strata when travel
ing in opposite directions. The action of
these atmospheric waves upon the surface
of the water tends to form minute undu-
lations, which increase in amplitude as
they move into bays, where the waite r
becomes shallower, until finally they as.
sumo the proportions as recorded upon
the instrument.
1t was found that marked 1apid and
large undulations often occnr during the
autumn and winter months upon both
instruments when the barometer is ac-
tually rising and fine weather prevails
over all the surrounding territory. The
explanation is that at such times an area
of low pressure, {. cyclone, is situated
over the South or Southern States. which
usually moves over or near to the lake
region. In such cases the recorded atmos