160 TABLES OF DIFFERENCES OF MEAN TEMPERATURES. 



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The vicinity of San Francisco, Cal., probably presents the greatest anomaly yet 

 noticed. Dr. H. Gibbons remarks^ that at San Francisco the warmest period of 

 the day in winter is from 1 to 2 P. M., but in summer (May to August) it is an hour 

 or two earlier owing to the sea breeze, which springs up about noon or soon after, 

 instantly depressing the temperature. In the season of the westerly breezes the 

 temperature is rapidly reduced and the change is effected long before sunset, after 

 which time the thermometer shows but little A^ariation till the following morning. 

 Under the influence of this brisk sea breeze, the rays of a high sun fail to impart 

 any appreciable heat to the air. These conditions are quite local and the attending 

 phenomena respecting the daily and annual fluctuations are confined to the vicinity 

 of the Bay of San Francisco, though traces of it appear at all stations along the 

 western coast exposed to the immediate influence of the westerly winds from the 

 Pacific ocean. Observations of the daily march of the temperature in these locali- 

 ties are specially desirable. For the study of the effect of height on the daily 

 fluctuation no material is at present available, but our records show that under this 

 condition it may become quite excessive; at elevated regions the air is comparatively 

 dry and the sun's rays reach the ground but little impeded, while at night radiation 

 is going on with great energy from the comparative absence of an absorbing medium. 

 The great interior basin bounded on the east by the Rocky Mountains and the 



The climate of San Francisco; Smithsonian Annual Report for 1854, p. 231 and foil. 



