THEORY OF WINDS. 323 



These general views have been greatly ex- 

 tended by Dr. Dalton and Mr. Daniel!. The 

 first of these philosophers observes, that the diur- 

 nal motion of the earth at the equator is 1040 miles 

 per hour, and diminishes gradually on to the 

 poles, where it is nothing. (Meteorological Es- 

 says, page 88.) And Mr. Daniell has demon- 

 strated in the most conclusive manner, that from 

 the greater density of the polar atmosphere than 

 the equatorial, its height is proportionably less ; 

 so that the expanded air between the tropics 

 must rise and flow towards the poles as an upper 

 current. Before rising, it has acquired the tro- 

 pical motion of the earth from west to east, 

 which it retains, until descending in higher lati- 

 tudes, where the earth's diurnal motion is less, 

 it mixes with the lower air, and gives it a west- 

 erly direction. 



The force and direction of the trade winds are 

 influenced by the proximity of islands and con- 

 tinents. Along the western side of Africa, their 

 direction is reversed. To the distance seaward 

 of about 300 miles, they blow towards the heated 

 land : they are reversed in a similar manner in 

 the Pacific, west of South America. When the 

 sun is in the northern tropic, they extend several 

 degrees farther north than during our winter ; 

 and when the sun is south of the equator, they 

 prevail farther south. 

 - There is a tract corresponding with the iso- 



