CLIMATE 269 



two modifications of temperature. It may reduce the ex- 

 tremes, making the atmosphere cooler in summer and 

 warmer in winter, and it may reduce or increase the mean 

 annual temperature. The Pacific coast of Alaska is within 

 the range of the prevailing westerly winds of the North- 

 ern Hemisphere. These winds come off the ocean, bring- 

 ing to the coast the temperature of the sea. As the sea 

 absorbs heat slowly, in comparison with the land, and 

 parts with it as slowly, the winds blowing off it are cool 

 in summer and warm in winter. Moreover, since the 

 ocean has waves, tides, and currents, by which its waters 

 are moved about, the cold water of the north toward the 

 south, and the heated water of the tropics toward the north, 

 there is a tendency to establish an equilibrium of tem- 

 perature. Thus the northern seas are warmer on the 

 whole that is, the mean annual temperature is higher 

 than land in the same latitudes, and through the agency 

 of the westerly winds the coast shares in this amelioration 

 of temperature. 



These same westerly winds are responsible for another 

 feature of the climate, the heavy rainfall. They come 

 from the sea saturated with moisture, and if they find the 

 land colder than they are, as it is in fall and winter, they 

 are chilled below the point of saturation and disgorge 

 copiously; but if they find the land warm, as it is in 

 summer, they carry their moisture inland and the coast 

 enjoys a comparatively dry season. This season is, how- 

 ever, dry only in comparison with the winter, the wet 

 season. The rainfall of the three winter months at Sitka 

 is commonly about 30 inches, while that of the three 

 summer months is 16 inches, or more than half that of 

 winter. 



The fogs of this coast, really the most obtrusive feature 

 of the climate, occur whenever the wind blows from the 

 sea, which it does most of the time, even in summer. For 



