SQO ■ PHILOSOPHICAL TRANSACTIONS. [aNNO 1755. 



greatest motion must be at the equator, and from thence lessen gradually to the 

 poles; and must be continued always equally one way, both day and night, and 

 at all seasons. But we find quite the contrary: the most gentle gales blowing 

 at the equator and between the tropics pretty steadily, one way all day long, and 

 dying away at night; while high winds and storms, blowing all manner of ways, 

 are found in the higher latitudes. Neither does he think that the sun's rarefying 

 air can simply be the cause of all the regular and irregular motions found in the 

 atmosphere; but he thinks the cause is the ascent and descent of vapour and 

 exhalation, attended by the electrical fire, or fluid. 



Now, all the vapour and exhalation, raised in the torrid zone, being buoyed 

 up by the electrical fire, must add a column to the air, though of a different 

 matter, at least 1000 times greater than the vapour and exhalation taken up; 

 which column must necessarily force the adjacent part of the incumbent air up- 

 wards, and must as necessarily be reacted on by the incumbent air, to restore 

 the equilibrium of the whole air. And as it cannot be readily forced down again, 

 it must float off, at that altitude, toward those parts where little or no addition 

 has been made to the atmosphere ; and by that means must propel the air on the 

 horizontal level with it, and that below it, as it is itself propelled by the weight 

 of the incumbent air. And that motion must be from the equator, where the 

 greatest quantity of vapour, &c. is raised, toward the poles, and partly to the 

 west; as the column of vapour is always rising from east to west, as the earth 

 turns toward the sun. For here we must confess, that the sun is the great agent 

 in detaching vapour and exhalation from their masses; whether he acts immedi- 

 ately by himself, or by his rendering the electric fire more active in its vibrations; 

 but their subsequent ascent Mr. E. attributes entirely to their being rendered 

 specifically lighter than the lower air, by their conjunction with this electrical 

 fire. The fire, which surrounds the vapour, beginning to condense, and the 

 vapour to subside, in passing the tropics, becomes a greater pressure on the air 

 beneath, and by that means forces some part back into the tropics, in the place 

 of that air protruded by the ascent of the vapour, &c. and the remainder in a 

 direction toward the poles. The common rotation of the air in coming in below, 

 to supply the place of that part carried up by any fire, may explain this motion. 

 To show how this motion must tend to the west, we must consider, that the 

 column of air, raised by the ascending vapour, &c. is at its greatest altitude to 

 the east, and therefore must press that air to the westward, which is continually 

 protruded by the vapours, &c. beginning to ascend from east to west; and the 

 compressed air at the tropics must tend to the westward, till their forces meeting 

 make the motion entirely to the west. The air itself being rarefied, and carried 

 up by the reflection of the intense heat of the sun, may be a considerable addi- 

 tional cause of these trade winds; but never can be the sole cause of all the 



