JOHN LE CONTE'S PHYSICAL STUDIES OF LAKE TAHOE
In certain numbers (November and December 1883 and January 1884) of
the _Overland Monthly_, Professor John Le Conte, of the State
University, Berkeley, California, presented the results of his
physical studies of Lake Tahoe in three elaborate chapters. From these
the following quotations of general interest are taken:
Hundreds of Alpine lakes of various sizes, with their clear,
deep, cold, emerald or azure waters, are embosomed among the
crags of the Sierra Nevada Mountains. The most extensive, as
well as the most celebrated, of these bodies of fresh water is
Lake Tahoe.
This Lake, ... occupies an elevated valley at a point where
the Sierra Nevada divides into two ranges. It is, as it were,
ingulfed between two lofty and nearly parallel ridges, one
lying to the east and the other to the west. As the crest of
the principal range of the Sierra runs near the western margin
of this Lake, this valley is thrown on the eastern slope of
this great mountain system.
The boundary line between the States of California and Nevada
makes an angle of about 131 degrees in this Lake, near its
southern extremity, precisely at the intersection of the 39th
parallel of north latitude with the 120th meridian west from
Greenwich. Inasmuch as, north of this angle, this boundary
line follows the 120th meridian, which traverses the Lake
longitudinally from two to four miles from its eastern
shore-line, it follows that more than two-thirds of its area
falls within the jurisdiction of California, the remaining
third being within the boundary of Nevada. It is only within a
comparatively recent period that the geographical coordinates
of this Lake have been accurately determined.
Its greatest dimension deviates but slightly from a medium
line. Its maximum length is about 21.6 miles, and its greatest
width is about 12 miles. In consequence of the irregularity of
its outline, it is difficult to estimate its exact area; but
it cannot deviate much from 192 to 195 square miles.
The railroad surveys indicate that the elevation of the
surface of its waters above the level of the ocean is about
6247 feet.
Its drainage basin, including in this its own area, is
estimated to be about five hundred square miles. Probably more
than a hundred affluents of various capacities, deriving their
waters from the amphitheater of snow-clad mountains which
rise on all sides from 3000 to 4000 feet above its surface,
contribute their quota to supply this Lake. The largest of
these affluents is the Upper Truckee River, which falls into
its southern extremity.
The only outlet to the Lake is the Truckee River, which
carries the surplus waters from a point on its northwestern
shore out through a magnificent mountain gorge, thence
northeast, through the arid plains of Nevada, into Pyramid
Lake. This river in its tortuous course runs a distance of
over one hundred miles, and for about seventy miles (from
Truckee to Wadsworth) the Central Pacific Railroad follows its
windings. According to the railroad surveys, this river makes
the following descent:
_Fall_
_Distance Fall per Mile_
Lake Tahoe to Truckee 15 Miles 401 Ft. 28.64 Ft
Truckee to Boca 8 " 313 " 39.12 "
Boca to State Line 11 " 395 " 35.91 "
State Line to Verdi 5 " 211 " 42.21 "
Verdi to Reno 11 " 420 " 38.18 "
Reno to Vista 8 " 103 " 12.87 "
Vista to Clark's 12 " 141 " 11.75 "
Clark's to Wadsworth 15 " 186 " 12.40 "
Wadsworth to Pyramid Lake 18[1] " 187[1] " 10.39 "
______ _______ _______
Lake Tahoe to Pyramid Lake 103 " 2357 " 23.11 "
[Footnote 1: The elevation of Pyramid Lake above the sea-level
has never, as far as we know, been accurately determined.
Henry Gannet, in his _Lists of Elevation_ (4th ed.,
Washington, 1877, p. 143), gives its altitude above the sea as
4890 feet; and credits this number to the _Pacific Railroad
Reports_. But as this exact number appears in Frémont's
_Report of Exploring Expedition to Oregon and North
California in the Years 1843-44_. (Doc. No. 166, p. 217),
it is probable that the first rude and necessarily imperfect
estimate has been copied by subsequent authorities. This
number is evidently more than 800 feet too great; for the
railroad station at Wadsworth (about eighteen or twenty miles
from the lake), where the line of the railroad leaves the
banks of the Truckee River, is only 4077 feet above the
sea-level. So that these numbers would make Pyramid Lake 813
feet above the level of its affluent at Wadsworth; which,
of course, is impossible. Under this state of facts, I have
assumed the elevation of this lake to be 3890 feet.]
During the summer of 1873, the writer embraced the opportunity
afforded by a six weeks' sojourn on the shores of the Lake to
undertake some physical studies in relation to this largest of
the "gems of the Sierra." Furnished with a good sounding-line
and a self-registering thermometer, he was enabled to secure
some interesting and trustworthy physical results.
(1.) _Depth_. It is well known that considerable
diversity of opinion has prevailed in relation to the
actual depth of Lake Tahoe. Sensational newsmongers have
unhesitatingly asserted that, in some portions, it is
absolutely fathomless. It is needless to say that actual
soundings served to dispel or to rectify this popular
impression. The soundings indicated that there is a deep
subaqueous channel traversing the whole Lake in its greatest
dimension, or south and north. Beginning at the southern end,
near the Lake House, and advancing along the long axis of the
Lake directly north towards the Hot Springs at the northern
end--a distance of about eighteen miles--we have the following
depths:
_Station Depth in Feet Depth in Meters_
1 ............... 900 274.32
2 ............... 1385 422.14
3 ............... 1495 455.67
4 ............... 1500 457.19
5 ............... 1506 459.02
6 ............... 1540 469.38
7 ............... 1504 458.41
8 ............... 1600 487.67
9 ............... 1640 499.86
10 ............... 1645 501.39
These figures show that this lake exceeds in depth the deepest
of the Swiss lakes (the Lake of Geneva), which has a maximum
depth of 334 meters. On the Italian side of the Alps, however,
Lakes Maggiore and Como are said to have depths respectively
of 796.43 and 586.73 meters. These two lakes are so little
elevated above the sea that their bottoms are depressed 587
and 374 meters below the level of the Mediterranean.
(2.) _Relation of Temperature to Depth_. By means of
a self-registering thermometer (Six's) secured to the
sounding-line, a great number of observations were made on the
temperature of the water of the Lake at various depths and
in different portions of the same. These experiments were
executed between the 11th and 18th of August, 1873. The same
general results were obtained in all parts of the Lake. The
following table contains the abstract of the average results,
after correcting the thermometric indications by comparison
with a standard thermometer:
Obs. in Feet in Meters F. deg. in C._
1 ...... 0-Surface 0-Surface 67 19.44
2 ...... 50 15.24 63 17.22
3 ...... 100 30.48 55 12.78
4 ...... 150 45.72 50 10.00
5 ...... 200 60.96 48 8.89
6 ...... 250 76.20 47 8.33
7 ...... 300 91.44 46 7.78
8 ...... 330 (Bottom) 100.58 45.5 7.50
9 ...... 400 121.92 45 7.22
10 ...... 480 (Bottom) 146.30 44.5 6.94
11 ...... 500 152.40 44 6.67
12 ...... 600 182.88 43 6.11
13 ...... 772 (Bottom) 235.30 41 5.00
14 ...... 1506 (Bottom) 459.02 39.2 4.00
It will be seen from the foregoing numbers that the
temperature of the water decreases with increasing depth to
about 700 or 800 feet (213 or 244 meters), and below this
depth it remains sensibly the same down to 1506 feet (459
meters). This constant temperature which prevails at all
depths below say 250 meters is about 4 degrees Cent. (39.2
Fah.). This is precisely what might have been expected; for it
is a well established physical property of fresh water,
that it attains its maximum density at the above-indicated
temperature. In other words, a mass of fresh water at the
temperature of 4 deg. Cent. has a greater weight under a
given volume (that is, a cubic unit of it is heavier at this
temperature) than it is at any temperature either higher or
lower. Hence, when the ice-cold water of the snow-fed streams
of spring and summer reaches the Lake, it naturally tends to
sink as soon as its temperature rises to 4 deg. Cent.; and,
conversely, when winter sets in, as soon as the summer-heated
surface water is cooled to 4 deg., it tends to sink. Any
further rise of temperature of the surface water during the
warm season, or fall of temperature during the cold season,
alike produces expansion, and thus causes it to float on
the heavier water below; so that water at 4 deg. Cent.,
perpetually remains at the bottom, while the varying
temperature of the seasons and the penetration of the solar
heat only influence a surface stratum of about 250 meters in
thickness. It is evident that the continual outflow of water
from its shallow outlet cannot disturb the mass of liquid
occupying the deeper portions of the Lake. It thus results
that the temperature of the surface stratum of such bodies of
fresh water for a certain depth fluctuates with the climate
and with the seasons; but at the bottom of deep lakes it
undergoes little or no change throughout the year, and
approaches to that which corresponds to the maximum density of
fresh water.
(3.) _Why the Water does not freeze in Winter_. Residents
on the shore of Lake Tahoe testify that, with the exception
of shallow and detached portions, the water of the Lake never
freezes in the coldest winters. During the winter months, the
temperature of atmosphere about this Lake must fall as low,
probably, as 0 degrees Fah. (-17.78 deg. Cent.). According to
the observations of Dr. George M. Bourne, the
minimum temperature recorded during the winter of 1873-74 was
6 deg. Fah. (-14.44 deg. Cent.). As it is evident that during
the winter season the temperature of the air must frequently
remain for days, and perhaps weeks, far below the freezing
point of water, the fact that the water of the Lake does not
congeal has been regarded as an anomalous phenomenon. Some
persons imagine that this may be due to the existence of
subaqueous hot springs in the bed of the Lake--an opinion
which may seem to be fortified by the fact that hot springs do
occur at the northern extremity of the Lake. But there is
no evidence that the temperature of any considerable body of
water in the Lake is sensibly increased by such springs. Even
in the immediate vicinity of the hot springs (which have in
summer a maximum temperature of 55 deg. C. or 131 F.), the
supply of warm water is so limited that it exercises no
appreciable influence on the temperature of that portion of
the Lake. This is further corroborated by the fact that no
local fogs hang over this or any other portion of the Lake
during the winter which would most certainly be the case if
any considerable body of hot water found its way into the
Lake.
The true explanation of the phenomenon may, doubtless, be
found in the high specific heat of water, the great depth of
the Lake, and in the agitation of its waters by the strong
winds of winter. In relation to the influence of depth, it
is sufficient to remark that, before the conditions preceding
congelation can obtain, the whole mass of water--embracing a
stratum of 250 meters in thickness--must be cooled down to
4 deg. Cent.; for this must occur before the vertical
circulation is arrested and the colder water floats on the
surface. In consequence of the great specific heat of
water, to cool such a mass of the liquid through an average
temperature of 8 deg. Cent, requires a long time, and the cold
weather is over before it is accomplished. In the shallower
portions, the surface of the water may reach the temperature
of congelation, but the agitations due to the action of
strong winds soon breaks up the thin pellicle of ice, which is
quickly melted by the heat generated by the mechanical action
of the waves. Nevertheless, in shallow and detached portions
of the Lake, which are sheltered from the action of winds and
waves--as in Emerald Bay--ice several inches in thickness is
sometimes formed.
[Illustration: Lily Lake]
[Illustration: Cave Rock, Lake Tahoe]
[Illustration: Pyramid Peak and Lake of the Woods]
[Illustration: Clouds Over the Mountain, Lake Tahoe]
(4.) _Why Bodies of the Drowned do not Rise_. A number of
persons have been drowned in Lake Tahoe--some fourteen
between 1860 and 1874--and it is the uniform testimony of the
residents, that in no case, where the accident occurred in
deep water, were the bodies ever recovered. This striking fact
has caused wonder-seekers to propound the most extraordinary
theories to account for it. Thus one of them says, "The water
of the Lake is purity itself, but on account of the highly
rarified state of the air it is not very buoyant, and swimmers
find some little fatigue; or, in other words, they are
compelled to keep swimming all the time they are in the water;
and objects which float easily in other water sink here like
lead." Again he says, "Not a thing ever floats on the surface
of this Lake, save and except the boats which ply upon it."
It is scarcely necessary to remark that it is impossible that
the diminution of atmospheric pressure, due to an elevation
of 6250 feet (1905 meters) above the sea-level, could sensibly
affect the density of the water. In fact, the coefficient of
compressibility of this liquid is so small that the withdrawal
of the above indicated amount of pressure (about one-fifth
of an atmosphere) would not lower its density more than one
hundred-thousandth part! The truth is, that the specific
gravity is not lower than that of any other fresh water of
equal purity and corresponding temperature. It is not less
buoyant nor more difficult to swim in than any other fresh
water; and consequently the fact that the bodies of the
drowned do not rise to the surface cannot be accounted for by
ascribing marvelous properties to its waters.
The distribution of temperature with depth affords a natural
and satisfactory explanation of the phenomenon, and renders
entirely superfluous any assumption of extraordinary lightness
in the water. The true reason why the bodies of the drowned
do not rise to the surface is evidently owing to the fact that
when they sink into water which is only 4 deg. Cent. (7.2
deg. Fah.) above the freezing temperature, the gases usually
generated by decomposition are not produced in the intestines;
in other words, at this low temperature the
bodies do not become inflated, and therefore do not rise to
the surface. The same phenomenon would doubtless occur in
any other body of fresh water under similar physical
conditions.[2]
[Footnote 2: It should be noted that since 1874 there have been
remarkably few deaths from drowning in Lake Tahoe, and that the major
cases of those referred to by Dr. LeConte were of workmen and others
who were generally under the influence of intoxicants.]
(5.) _Transparency of the Water_. All visitors to this
beautiful Lake are struck with the extraordinary transparency
of the water. At a depth of 15 to 20 meters (49.21 to 65.62
feet), every object on the bottom--on a calm sunny day--is
seen with the greatest distinctness. On the 6th of September,
1873, the writer executed a series of experiments with the
view of testing the transparency of the water. A number of
other experiments were made August 28 and 29, under
less favorable conditions. By securing a white object of
considerable size--a horizontally adjusted dinner-plate
about 9.5 inches in diameter--to the sounding-line, it
was ascertained that (at noon) it was plainly visible at a
vertical depth of 33 meters, or 108.27 English feet. It must
be recollected that the light reaching the eye from such
submerged objects must have traversed a thickness of water
equal to at least twice the measured depth; in the above
case, it must have been at least 66 meters, or 216.54 feet.
Furthermore, when it is considered that the amount of
light regularly reflected from such a surface as that of a
dinner-plate, under large angles of incidence in relation
to the surface, is known to be a very small fraction of
the incident beam (probably not exceeding three or four per
cent.), it is evident that solar light must penetrate to
vastly greater depths in these pellucid waters.
Moreover, it is quite certain that if the experiments
in relation to the depths corresponding to the limit of
visibility of the submerged white disk had been executed in
winter instead of summer, much larger numbers would have been
obtained. For it is now well ascertained, by means of the
researches of Dr. F.A. Forel of Lausanne, that the waters of
Alpine lakes are decidedly more transparent in winter than in
summer. Indeed, it is reasonable that when the affluents of
such lakes are locked in the icy fetters of winter, much less
suspended matter is carried into them than in summer, when all
the sub-glacial streams are in active operation.
Professor Le Conte goes into this subject (as he later does into the
subject of the color of Lake Tahoe) somewhat exhaustively in a purely
scientific manner and in too great length for the purposes of this
chapter, hence the scientific or curious reader is referred to the
original articles for further information and discussion.
_Color of the Waters of Lake Tahoe_. One of the most
striking features of this charming mountain Lake is the
beautiful hues presented by its pellucid waters. On a calm,
clear, sunny day, wherever the depth is not less than from
fifty to sixty meters, to an observer floating above its
surface, the water assumes various shades of blue; from a
brilliant Cyan blue (greenish-blue) to the most magnificent
ultramarine blue or deep indigo blue. The shades of blue
increasing in darkness in the order of the colors of the
solar spectrum, are as follows: Cyan-blue (greenish blue),
Prussian-blue, Cobalt-blue, genuine ultramarine-blue, and
artificial ultramarine-blue (violet blue). While traversing
one portion of the Lake in a steamer, a lady endowed with a
remarkable natural appreciation and discrimination of shades
of color declared that the exact tint of the water at this
point was "Marie-Louise blue."
The waters of this Lake exhibit the most brilliant blueness
in the deep portions, which are remote from the fouling
influences of the sediment-bearing affluents, and the washings
of the shores. On a bright and calm day, when viewed in the
distance, it had the ultramarine hue; but when looked fair
down upon, it was of almost inky blackness--a solid dark
blue qualified by a trace of purple or violet. Under these
favorable conditions, the appearance presented was not unlike
that of the liquid in a vast natural dyeing-vat.
A clouded state of the sky, as was to be expected, produced
the well-known effects due to the diminished intensity of
light; the shades of blue became darker, and, in extreme
cases, almost black-blue. According to our observations,
the obscurations of the sky by the interposition of clouds
produced no other modifications of tints than those due to
a diminution of luminosity.
In places where the depth is comparatively small and the
bottom is visibly white, the water assumes various shades
of green; from a delicate apple-green to the most exquisite
emerald-green. Near the southern and western shores of the
Lake, the white, sandy bottom brings out the green tints very
strikingly. In the charming _cul-de-sac_ called "Emerald
Bay," it is remarkably conspicuous and exquisitely beautiful.
In places where the stratum of water covering white portions
of the bottom is only a few meters in thickness, the green hue
is not perceptible, unless viewed from such a distance that
the rays of light emitted obliquely from the white surface
have traversed a considerable thickness of the liquid before
reaching the eye of the observer.
The experiments with the submerged white dinner-plate,
in testing the transparency of the water, incidentally
manifested, to some extent, the influence of depth on the
color of the water. The white disk presented a bluish-green
tint at the depth of from nine to twelve meters; at about
fifteen meters it assumed a greenish-blue hue, and the blue
element increased in distinctness with augmenting depth,
until the disk became invisible or undistinguishable in the
surrounding mass of blue waters. The water intervening between
the white disk and the observer did not present the brilliant
and vivid green tint which characterized that which is seen in
the shallow portions of the Lake, where the bottom is white.
But this is not surprising, when we consider the small amount
of diffused light which can reach the eye from so limited a
surface of diffusion.
In studying the chromatic tints of these waters, a hollow
pasteboard 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 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 the 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 coöperation 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
wave 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 would give the most satisfactory
results; but any graduated gauge, systematically observed,
would soon furnish evidence of the phenomenon. For the
longitudinal _Seiches_, "Hot Springs," at the northern
extremity of the Lake, or "Lake House," at the southern end,
would be eligible stations for gauges; and for the transverse
_Seiches_, Glenbrook, on the eastern shore, or Capt.
McKinney's on the western margin, would afford good stations.
As far as I am aware, true _Seiches_ have never been
observed in any of the American lakes. This fact is the more
remarkable from the circumstance that long-continued and
careful observations have been made on the fluctuations of
level of several of the large Canadian lakes, with the view of
testing the possible existence of lunar tides. Perhaps these
lakes may be too large to manifest the uninodal rhythmical
oscillations which have been so successfully studied by Forel
in the smaller lakes of Switzerland.[3]
Be this as it may, there can be no doubt that Lake Tahoe is a
body of water in all respects adapted for the manifestation of
this species of oscillation; and that, like the Swiss lakes,
it is subject to _Seiches_. Indeed, the far greater
simplicity in the configuration of the basin of Lake Tahoe
than that of the Lake of Geneva must render the phenomena much
less complicated in the former than in the latter.
Professor LeConte then gives his computations as to the probable
duration of the oscillations on Lake Tahoe, should they occur there.
[Footnote 3: It is proper to add that _Fluctuations of level in the
North American lakes_ have been noticed by various observers, from
the time of the Jesuit Fathers of the period of Marquette, in 1673,
down to the present epoch. Among those who have discussed this problem
may be mentioned in chronological order: Fra Marquette in 1673, Baron
La Hontan 1689, Charlevoix 1721, Carver 1766, Weld 1796, Major S.A.
Storrow 1817, Capt. Henry Whiting 1819, H.R. Schoolcraft 1820, Gen.
Dearborn 1826-29.]