THE CLIMATOLOGY OF THE UNITED STATES. 37 



Winter. The position of these mountain ranges running 

 north and soiith in connection with the steady westerly 

 wind produces (as has been stated) a great variety of 

 temperatures. In San Francisco the thermometer regis- 

 tered 80^ not more than five or six times in the siimmer 

 and the average would be about 75°. When the interior 

 Valleys become a little cooler the trade wind becomes 

 weaker and the weather warmer. On this account July 

 and August are the coolest months and June and Sep- 

 tember are generally a few degrees warmer. 



What are called dog days in the east are scarcely known 

 on the Pacific Coast. When we reach Sacramento we ex- 

 perience a summer heat of 90° and as we go north or 

 south towards the heads of the two great Valleys we get 

 beyond even the slight influence of the trade wind which 

 Sacramento feels, and the temperature rises to 100° and 

 over, and occasionally the mercury registers 110° in the 

 shade ; but, owing to the dryness of the air, a temperature 

 of 100° is no more trying tlian one of 85° in New York, 

 and this region has the advantage of cool nights ; though 

 the people of Sacramento have a mid-day heat of 90° they 

 find blankets necessary at night. 



The winters here are colder than on the coast but therain- 

 fall is less, averaging about nineteen inches only ; these 

 Valleys sometimes have nearly two hundred and fifty 

 clear days in the year without fog or clouds. The rain- 

 fall increases from the southern part of the state towards 

 the north. It is greatest near the coast, and is generally 

 more on the western sides of the mountains than on the 

 eastern ; the amount is however quite variable from year 

 to year. It averages in San Francisco twenty-three and 

 one-half inches, at Santa Barbara fifteen inches, at Los 

 Angeles twelve inches, at San Diego ten inches, and 

 at Colton nine inches per year. The Los Angeles region 



