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Page:Popular Science Monthly Volume 57.djvu/85

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MOUNT TAMALPAIS.

not seriously affected by the local indraught of air through the Golden Gate and adjacent gaps in the Coast Range. This local indraught is a disturbing and often a misleading factor in all observations taken near and south of the Golden Gate for at least a score of miles. The elevated station on top of the peak eliminates the source of errors based upon observations at lower stations, and enables the forecast official to determine the effects of the local disturbances, and thus to give observations taken at or near sea level their true weight at the proper time.

2. 'No station in the United States has so full and free a projection into the lower third of the vapor-bearing stratum as has the station on this peak. No other station furnishes, as it does, an opportunity to study the distribution of vapor in the lower third of that stratum of the atmosphere, the physics of which is most important to human life and industries.

3. In studying the phenomena connected with the occurrence of fog, this station furnishes highly valuable data that could be obtained from no other; and, again, enables the student of weather lore to correct misleading impressions and deductions based upon observations taken below the one-thousand-foot contour above sea level.

On the 16th of June, 1899, the observations taken on Mount Tamalpais marked a difference of about thirty degrees in temperature over those around its base. In San Francisco, at Point Lobos and at Point Reyes, the temperature was down to 48°, while on Mount Tamalpais it was 79°, thus marking an approaching change in weather conditions, and giving the Weather Bureau the first opportunity of using the vertical temperature gradient in forecasting.

As a station for furnishing the data for a study of the problems of the physics of the atmosphere Mount Tamalpais is of further importance, as it stands near the easterly limits of the great area of high pressure which, during summer, lies over the North Pacific and which dominates the climatic phenomena of California for the greater portion of the year.

Stations on the Hawaiian Islands to the south and others on the Aleutian Islands to the north of this area of high pressure will still further aid in the solution of the great and vital problems now before meteorologists. These stations are the most reliable ones which can surround on three sides the two great "weather breeders"—the "summer high" and the "winter low" of the North Pacific.