THE WEATHER, AND WEATHER PROPHETS. 157 



follow the directions of meridians, but are converted by 

 its rotation on its axis and the gradual diminution of the 

 rotatory velocity in advancing from the equator to the 

 poles, into relatively oblique currents. The upper or out- 

 ward follow precisely the reverse direction to the lower 

 or inward, and being drawn downwards, and are ultimately 

 brought down to the sea level, in their approach towards 

 the poles to supply the void which would otherwise be 

 left by the withdrawal of air below.* They thus become 

 surface winds, prevalent in the regions beyond the tropics 

 from about 30 of latitude either way. 



(19.) In the view thus taken of the great and per- 

 manent system of winds known as the " trades" and 

 " anti-trades," it will be observed that we have been 

 careful to regard them as resulting not so much from the 

 immediate (and diurnally intermittent) action of the sun, 

 as in a certain established gradation of climatic tem- 

 perature, the result of its action on the whole earth's 

 surface continued through successive ages. Were the 

 sun extinguished, the system of the trade winds would 

 continue to subsist, though with diminishing intensity, 

 so long as the equator continued in any degree warmer 

 than the poles. 



(20.) By the action of the trade winds which occupy 



* Those of our readers who are not already familiar with the 

 nature of this transformation, and who would wish to follow it out 

 more closely, are referred (as well as for every other matter of detail 

 in similar cases, precluded by our limits) to the article Meteorology, 

 in the " Encyclopaedia Britannica," or to the same article pub- 

 lished separately by (A. & C. Black, Edinburgh) the editors of 

 that work. 



