118 PHYSICAL GEOGRArnT OF THE SEA, AND ITS METEOROLOGY. 



rain in the north temperate zone is half as mnch again as that of 

 the south temperate. How is it, then, that this vapour gets, as 

 stated, from the southern into the northern hemisphere, and 

 comes with such regularity that our rivers never go dry and our 

 springs fail not? It is because of these air-crossings — these 

 beautiful operations, and the exquisite compensation of this grand 

 niaehiiie, the atmosphere. It is exquisitely and wonderfully 

 counterpoised. Late in the autumn of the north, throughout its 

 winter, and in early spring, the sun is pouring his ra3"S with the 

 greatest intensity down upon the seas of the southern hemisphere, 

 and this wonderful engine which we are contemplating is pump- 

 ing up the water there (§ 208) with the gi'eatest activity, and 

 sending it over here for our rivers. The heat which this heavy 

 evaporation absorbs becomes latent, and, with the moisture, is 

 carried through the upper regions of the atmosphere until it 

 reaches our climates. Here the vapour is formed into clouds, 

 condensed, and precipitated. The heat which held this water in 

 the state of vapour is set free, it becomes sensible heat, and it is 

 that [ (4), § 288] which contributes so much to temper our 

 winter climate. It clouds up in winter, turns warm, and we 

 say we are going to have fallen weather. That is because the 

 process of condensation has already commenced, though no rain 

 or snow may have fallen : thus we feel this southern heat, that 

 has been collected from the rays of the sun by the sea, been 

 bottled away by the winds in the clouds of a southern summer, 

 and set free in the process of condensation in our northern 

 winter. If Plate I. fairly represent the course of the winds, the 

 south-east trade-winds would enter the northern hemisphere, 

 and, as an upper current, bear into it all their moisture, except 

 that which is precipitated in the region of equatorial calms, and 

 in the crossing of high mountain ranges, such as the Cordilleras 

 of South America. 



291. Moi'e rain in the northern than in the southern hemisphere. — 

 The South Seas, then (§ 290), should supply mainly the water 

 for this engine, while the northeni hemisphere condenses it ; we 

 should, therefore, have more rain in the northern hemisphere. 

 The rivers tell us that we have — the rain-gauge also. The 

 yearly average of rain in the north temperate zone is, according 

 to Johnston, thirty-seven inches. He gives but twent^^-six in the 

 south temperate. The observations of mariners are also cor- 

 roborative of the same. Log-books, containing altogether the 



