168 Prof. E. Mitchell un the Proximate 



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 Hmited extent 

 where local causes have a decided effect excepted) a predomi- 

 nance of winds blowing from the poles towards the equator, 

 over those moving in the opposite direction; — but this predomi- 

 nance is not so well marked and decided as that of the westerly 

 over the easterly winds, between the latitudes of 30° and CO". 



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 thunder-storm. Thun- 

 der-storms generally commence between mid-day and sunset, 

 and move from west to east. 



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

 quire to be viewed in connexion with the laws which regulate 

 the movements 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 respect- 

 ino- the causes by which the facts asserted in them may be sup- 

 posed to be produced. 



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

 parallel of latitude on both sides of the equator, is constantly 

 swept by a wind varying but a feio 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 proximity of islands and continents. 

 Along the western side of Africa their direction is reversed ; to 

 the distance seaward of about three hundred miles, they blow 

 towai'ds the land, and nearly at right angles to the coast. 



Halley notices a tract between the 4th and 10th degrees of 

 north latitude, and the longitudes of 17° and 23°, " wherein it 



