248 Proximate Causes of certain Winds and Storms. 



Art. VI. — On the proximate causes of certain, Winds and Storms; 

 by Prof. E. Mitchell, Univ. of North Carolina. 



The four following propositions may be regarded as statements of 

 general facts which have been sufficiently established by numerous 

 observations in various parts of the world. 



I. That part of the great oceans which lies between the 30th par- 

 allel of latitude on both sides of the equator, is constantly swept by 

 a wind varying but a few points from the east. 



II. Between the latitudes of 30° and 60°, in both the northern and 

 southern hemisphere ', westerly winds predominate over those from the 

 east quarter in a ratio probably somewhat greater than that of 3 to 2. 



III. There is in all latitudes, (a few tracts of limited extent where 

 local causes have a decided effect excepted,) a predominance of 

 winds blowing from the poles towards the equator, over those moving 

 in the opposite direction — but this predominance is not as well mark- 

 ed and decided as that of the westerly over the easterly winds, be- 

 tween the latitudes of 30° and 60°. 



IV. During the warm weather within the temperate, and at all 

 seasons within the limits of the torrid zone, the fall of rain is often 

 accompanied by lightning, thunder and violent winds, constituting 

 what is commonly called a thunderstorm. Thunderstorms generally 

 commence between mid-day and sunset, and move from west to east. 



Other general facts might be added, but these are such as require 

 to be viewed in connexion when the laws which regulate the move- 

 ments of the aerial currents over the surface of the globe, and the 

 origin of those currents are to be investigated. The truth of the 

 statements contained in these propositions will first be shewn, after 

 which an inquiry will be instituted respecting the causes by which 

 the facts asserted in them may be supposed to be produced. 



I. That part of the great oceans which lies between the 30th par- 

 allel of latitude on both sides of the equator, is constantly swept by 

 a wind varying but a few points from the east. 



The direction, velocity, permanence and other characters of the 

 trade winds, are too well known to require any particular remark. 

 They are affected by a number of local causes. Near the equator 

 they blow from the east point, but at a distance from it their course 

 becomes inclined to the parallels of latitude, so as to be at length 

 from the north east and south east, near their northern and southern 

 limits. Their force and direction are also influenced by the prox- 

 imity of islands and continents. Along the western side of Africa, 



