328 TRANSACTIONS OF THE 



west wind. The greater part of this upper current having descended to 

 the earth within 30° and returned to join the trade wind, the remainder 

 would flow toward the pole, portions descending in its course at all points 

 where the rarefaction of the air near the earth's surface would permit. 

 These descending currents cause the local variable winds of our temperate 

 zone, but the aggregate of all of them is the prevailing southwest return 

 trade wind. The descending currents cannot give rain, as they only fall 

 to the earth when they become colder than the air near the earth's surface. 

 In falling they are constantly arriving at places of warmer temperature 

 than those they have left; therefore they change to a condition of taking 

 up moisture, rather than of parting with it. Where the great body of the 

 descending return trade wind reaches the earth between latitudes 28° and 

 35° must, therefore, on this coast, be comparatively a rainless region. Other 

 lessening portions of the upper current would pass on until they met the 

 prevailing northerly wind from the polar regions, when their temperature 

 would be lowered and their moisture condensed and fall as rain. The con- 

 flict of this descending current with the polar wind would create storms 

 and give rise to electrical phenomena. The prevailing northerly polar 

 wind reaches to about latitude 60°, varied by the declination of the sun. 



The cause of this dry season is supposed to be the return trade winds 

 deprived of their moisture, which prevail during the Summer months. 



On the other hand, beginning in September, the wind currents are from 

 the south. These winds are saturated with moisture from the Gulf of 

 California and other southern tropical seas. They lose but little moisture 

 passing over the hot deserts and valleys of southern California, and it is 

 only as they reach the cool coast, from Santa Barbara northward, that the}' 

 deposit much rain. The further north they go the more they are affected 

 by the coolness incident to a higher latitude. 



For the same reasons it has been supposed that moisture-bearing west 

 winds would deposit more rain in the northern than in the southern part 

 of California. It is not probable that this increased rainfall is due alto- 

 gether to a colder latitude. The temperature is not such as to be a power- 

 ful condenser. The mercury seldom falls below 50°, and, if it were this 

 temperature that condensed the moisture of the west wind, this condensa- 

 tion should take place in the Summer as well as the. Winter, the variation 

 in temperature between these seasons being slight. During the months of 

 October, November, and December, 1885, an unusually large amount of 

 rain fell on the northern coast, but during this time the temperature did 

 not fall below 60°, and no snow fell either on the Coast Range or in the 

 Siskiyou Mountains. 



Professor John Le Conte has suggested the possibility of a cold counter 

 current going north which hugs the shore and which might act as a con- 

 denser. Another possible explanation is the influence of the immense 

 forests already mentioned. 



COAST CLIMATE. 



The annual temperature of the coast ranges from 45° to 60°. Snow is a 

 most rare visitor, though, at intervals of a few years, there is a slight fall . 

 In the early Spring months frost occasionally occurs. 



To one accustomed to the enervating heat of the great interior valleys, 

 a sudden change to the coast is not pleasant. 



The ocean breezes are possessed of a peculiar " freshness " that sends 

 unpleasant chills through the newcomer, unless he be unusually vigorous. 

 A few weeks residence changes this rawness into an agreeable state of 



