Facts in Meteorology. 125 



The dry current of the north-east Monsoon, on approaching the 

 equator, becomes deflected and checked in its course, and crossing 

 the equator, returns again to the eastward, in the southern latitudes, 

 in the form of the wet north-west Monsoon. On the other hand, the 

 dry south-east Monsoon which prevails in the opposite season south 

 of the equator, becomes deflected in the same manner, in the equa- 

 torial region, and returns to the eastward north of the equator in the 

 character of the south-west Monsoon. 



In Ceylon, (lat. 8° north) the north-east Monsoon, with a tempe- 

 rature of 68° Fahrenheit, has a dryness of 75 hygrometric degrees. 

 The opposite Monsoon, from the south-west at 82° Fahrenheit, is so 

 damp as to indicate but 30°. 



Of General Winds and atmospheric phenomeiia. 



As the winds, over a breadth of 60 degrees, blow with slight in- 

 terruption, from east to west; so in the northern and southern hem- 

 ispheres the atmospheric equilibrium demands that the prevailing 

 winds should be from west to east, and therefore, for the most part, 

 westerly winds prevail for two thirds of the year, and they enable 

 ships which sail to the West Indies by the trade winds to return to 

 the East by first ascending to the latitude of 40° or 45°. 



In almost every country, as well as in every sea, the wind is more 

 or less predominant in a particular direction. 



From the average rate of sailing of ships during long voyages 

 through various seas, as in the China trade, and from other data, it is 

 estimated that the average velocity of the wind, near the surface of 

 the ocean, is equal to eighteen miles an hour throughout the year. 



Notwithstanding these general and determinate horizontal move- 

 ments, the equal distribution of the atmosphere over the surface of 

 the globe, which results from gravitation, tends to prevent any very 

 rapid or violent motion in any specific direction, and consequently to 

 prevent violent and destructive winds. But owing to the tendency 

 of all fluid matter to run in whirls, or circuits, when subject to the 

 influence of unequal or opposing forces, a rotative movement of un- 

 measured violence is sometimes produced. This peculiar movement 

 which in its most active state is sometimes distinguished by the name 

 of tornado or hurricane, assumes every possible variety of position, 

 appearance, velocity and extent ; and is the only known cause of 

 violent and destructive winds or tempests, 



