88 THE PHYSICAL GEOGRAPHY OF THE SEA. 



tlie southern into tlie northern hemisphere, and comes with such 

 regularity that our rivers never go dry and our springs fail not ? 

 It is because of the beautiful operations and the exquisite com- 

 pensati07i of this grand machine, the atmosphere. It is exquis- 

 itely and wonderfully counterpoised. Late in the autumn of the 

 north, throughout its winter, and in early spring, the sun is pour- 

 ing his rays with the greatest intensity down upon the seas of the 

 southern hemisphere, and this powerful engine which we are con- 

 templating is pumping up the water there (§ 169) for our rivers 

 with the greatest activity. At this time, the mean temperature 

 of the entire southern hemisphere is said to be about 10° higher 

 than the northern. 



172. The heat which this heavy evaporation absorbs becomes 

 latent, and, with the moisture, is carried through the upper re- 

 gions of the atmosphere until it reaches our climates. Here the 

 vapor is formed into clouds, condensed, and precipitated. The 

 heat which held this water in the state of vapor is set free, it be- 

 comes sensible heat, and it is that which contributes so much to 

 temper our winter climate. It clouds up in winter, turns warm, 

 and we say we are going to have falling weather. That is be- 

 cause 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. 



173. If the Plate at page 75 fairly represent the course of the 

 winds, the southeast trade-winds would enter the northern hemi- 

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

 except that which is precipitated in the region of equatorial calms. 



174. The South Seas, then, according to § 168, should supply 

 mainly the water for this engine, while the northern hemisphere 

 condenses it ; we should, therefore, have more rain in the northern 

 hemisphere. The rivers tell us that we have — at least on the land : 

 for the great water-courses of the globe, and half the fresh water 

 in the world, are found on our side of the equator. This fact 

 alone is strongly corroborative of this hypothesis. 



175. The rain gauge tells us also the same story. The yearly 



