Some very interesting information by Prof. John Le Conte, is given in the Overland Monthly, being the result of some physical observations made by the author at Lake Tahoe, in 1873. Lake Tahoe, also called Lake Bigler, is situated at an altitude of 6,247 feet in the Sierra Nevada Mountains, partly in California, partly in Nevada. The lake has a length of 22 and a width of 12 miles. As regards its origin, the author regards it as a "plication hollow," or a trough produced by the formation of two mountain ridges, afterward modified by glacial agency. The depth of the lake is remarkable; the observations taken at ten stations along the length of the lake gave the following depths in feet: 900, 1,385, 1,495, 1,500, 1,506, 1,540, 1,504, 1,600, 1,640, 1645. This depth exceeds that of the Swiss lakes proper--Lake Geneva, for example, has a maximum depth of 1,096 feet--but is considerably less than that of Lakes Maggiore and Como, on the Italian side of the Alps. A series of observations of the temperature of the water were taken between the 11th and 18th of August. The average corrected results are as follows:

The temperature, therefore, diminishes with increasing depth to about 700 or 800 feet, and below this remains sensibly the same down to 1,506 feet; or in other words, a constant temperature of 4° C. prevails at all depths below about. 820 feet. This is in accordance with the theory, the temperature named being that of the maximum density of water, and it confirms the recent observations of Prof. Forel in Switzerland; he found, for example, that a constant temperature of 4° C. was reached in Lake Zurich at a depth of nearly 400 feet, the lake being then covered with 4 inches of ice. The explanation of the observed fact that Lake Tahoe does not entirely freeze over even in severe winters is found in the extreme depth; and the fact that the bodies of drowned persons do not rise to the surface after the lapse of the usual time is explained by the low temperature prevailing near the bottom, which does not allow the necessary decomposition to go forward so as to produce the ordinary result.

The water of Lake Tahoe is remarkable both for its transparency and beauty of color. A series of observations made at the close of August or beginning of September showed that a horizontally adjusted dinner plate of about 9½ inches diameter was visible at noon at a depth of 108 feet. The maximum depth of the limit of visibility as found by Prof. Forel, in Lake Geneva, was 56 feet. He showed, moreover, that this limit is much greater in. winter than in summer, as explained in part by the greater absence of suspended matter and in part by the fact that increase of temperature increases the absorbing power of water for light. The maximum depth of visibility in the Atlantic Ocean, as found by Count de Pourtales, was 162 feet, and Prof. Le Conte states his belief that winter observations in Lake Tahoe would place the limit at even a greater depth than this. The author gives a detailed and interesting discussion in regard to the blue color of lake waters, reviewing in full the results of previous writers on the subject, and concludes that while pure water unquestionably absorbs a larger part of the red end of the spectrum, and hence appears blue by transmitted light, the color seen by diffuse reflection is mainly due to the selective reflection from the fine particles suspended in it.

The last subject discussed by the author is that of the rhythmical variations of level, or "seiches," of deep lakes; he applies the usual formula to Lake Tahoe, and calculates from it the length of a complete longitudinal and of a transverse "seiche;" these are found to be eighteen or nineteen minutes in the first case and thirteen minutes in the second.

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