MOUNT TAMALPAIS. 75 



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 obser- 

 vations 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 pro- 

 jection into the lower third of the vapor-bearing stratum as has 

 the station on this peak. ]STo 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 temper- 

 ature 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. 



