88 RESOURCES OF CALIFORNIA. 



be supplied by the breezes from the ocean. These leave the 

 surface of the Pacific ordinarily with a temperature of 50 a , 

 and as they advance inland, it rises. Thus, the mean temper- 

 ature of July in San Francisco is 57, in Yallejo 63, Sacra- 

 mento 73, and St. Helena 77, the difference being due to the 

 greater or less exposure of these several places to the winds 

 from the ocean. Two valleys, on the same level, only five 

 miles apart, but separated by a high mountain ridge which 

 protects the more eastern of the two from the sea breeze, 

 may have a difference of 10 in their summer weather. 



Strong winds blow almost constantly through the gaps in 

 the Coast ridge. 



As the sea breeze prevails in the day-time, so the land breeze 

 comes in the summer nights, and although not strong enough 

 to be noticed in many parts of the State, it is regularly felt in 

 certain gaps on the southern coast, and in canons of the Sierra 

 Xevada. The air pouring down from the snow of the summit 

 of the Sierra, helps to cool the nights in the valleys. 



65. Middle Coast. On the coast, between latitudes 35 

 and 40, there is little difference in the temperatures of winter 

 and summer. San Francisco is in the same latitude with 

 Seville, Palermo, Smyrna, Washington, and St. Louis, but 

 knows neither the cold winters nor the hot summers which 

 afflict American cities east of the Rocky Mountains in the 

 same latitude. Ice is rarely formed in the California!! metrop- 

 olis, and never more than an inch in thickness ; and the ther- 

 mometer never stays at the freezing point twenty-four consec- 

 utive hours. The lowest point which the thermometer has 

 ever reached in San Francisco, since observations have been 

 taken, was 22 Fahrenheit in January, 18G2 ; and previous to 

 that time it had never fallen below 25 ; while in St. Louis it 

 goes down to 12 every winter, and remains near that figure 

 for many consecutive days. The mean temperature of January 

 at sunrise is 44, and the coldest noon, according to Dr. H. 

 Gibbons, between 1850 and 1868, was 37. In three years 



