CLIMATE. 



291 



ments of either temperature or rainfall by yearly means are 

 of little practical interest to the farmer. \Yhat he needs to 

 know is whether or not sufficient rains to mature a full crop 

 are likely to fall during the time that the growing temperature 

 prevails ; and what are the minima and maxima of temperature 

 heat and cold that his crops will be called upon to endure. 



WINDS. 



The third climatic factor mentioned, the winds, though 

 proverbial for their unreliability and inconstancy, are not only 

 very incisive in their action, but also to a considerable 

 extent of very definite local or regional occurrence and signifi- 

 cance. Moreover, their occurrence, direction, temperature and 

 moisture-condition can, in regions whose climatology has been 

 reasonably well studied, be foretold with sufficient accuracy 

 to be of great use to the farmer. 



Heat the Cause of IVinds. As already stated, the primary 

 cause of all winds is heat, substantially on the principle accord- 

 ing to which draught is created in our domestic fires. The 

 hot air rising creates an indraught from all directions, especi- 

 ally from that which it can most readily come; viz., from 

 the ocean, 1 or from level lands, rather than across mountain 

 chains. Hence the sea-breeze in the after part of the day, when 

 the land has become heated; while the sea. requiring a much 

 larger amount of heat to change its temperature to a similar 

 extent, remains relatively cool. Rut at night the earth cools 

 more rapidly than the sea, by radiation; hence toward evening 



1 A striking case in point is the regular wind which in summer blows through 

 the " Golden Gate," a gap in the Coast Range connecting the Pacific Ocean 

 directly with the great interior valley of California, along the hays of San 

 Francisco, San Pablo, and Suisun. The great interior valley and adjacent moun- 

 tain slopes becoming intensely heated during the rainless summer, the ascending 

 air is replaced by a steady indraught from the sea, which is bordered by a belt of 

 cold water causing fogs along the coast. The fogs are quickly dispelled on reach- 

 ing the edge of the valley near the middle of its length ; whence steady bree/es 

 blow northward and southward, up the valleys of the Sacramento and San 

 Joaquin respectively. These winds, popularly often, but erroneously, called trade- 

 winds, are really " monsoons " similar in their origin to those of India, which, 

 when coming from the sea cause rains, but when from the heated land itself are 

 hot and dry; as in the case of the sirocco of Italy and Xorth Africa, the terral of 

 Spain and the northers of California. 



