326 PHILOSOPHICAL TRANSACTIONS. [aNNO lOSS. 



In the foregoing history are contained several problems, that merit well the 

 consideration of the acntest naturalists, both' by reason of the constancy of 

 the effect, and its vast extent. The chief of these problems are, i. Why 

 these winds are perpetually from the east in the Atlantic, Ethiopic, and 

 Pacific oceans, between the latitudes of 30 north and south. 2. Why the said 

 winds extend no farther, with constancy, than to the latitudes of 30°. 3. Why 

 there should be a constant south-westerly wind upon and near the coast of 

 Guinea. 4. Why in the north part of the Indian ocean the winds, which for 

 , one half year agree with those of the other two oceans, should change in the 

 other half year, and blow from the opposite points ;' while the southern part of 

 that ocean follows the general rule, and has perpetual winds about south-east. 

 5. Why, in these general trade-winds, it should always hold, that to the north- 

 ward of the equator, it is inclined to the northward of the east ; and in south 

 latitudes, to the southward of it. 6. Why, in the seas of China, there should 

 be so great an inclination from the east to the north, more than elsewhere. 



To attempt a solution of the foregoing phaenomena, it may be observed that 

 wind is most properly defined to be the stream or current of the air ; and where 

 , such current is perpetual and fixed in its course, it is necessary that it proceed 

 from a permanent unintermitting cause. Therefore some have been inclined 

 to propose the diurnal rotation of the earth on its axis; by which, as the globe 

 turns eastwards, the loose and fluid particles of the air, being so exceedingly 

 light, are left behind ; so that, in respect of the earth's surface, they move 

 westwards, and become a constant easterly wind. This opinion seems confirmed 

 by these winds being found only near the equinoctial, in those parallels of lati- 

 -tude where the diurnal motion is swiftest ; and I should readily assent to it, if 

 the constant calms in the Atlantic sea near the equator, the westerly winds near 

 the coast of Guinea, and the periodical westerly monsoons under the equator 

 in the Indian seas, did not show the insufficiency of that hypothesis. Besides, 

 the air being kept to the earth by the principle of gravity, would acquire the 

 same degree of velocity that the earth's surface moves with, as well in respect 

 of the diurnal rotation, as of the annual about the sun, which is about 30 times 

 swifter. 



It remains therefore to substitute some other cause, capable of producing a 

 like constant effect, not liable to the same objections, but agreeable to the 

 known properties of the elements of air and water, and the laws of the motion 

 of fluid bodies. And such seems to be the action of the sun beams on the air 

 and water, as he passes every day over the ocean, considered together with the 

 nature of the soil, and situation of the adjoining continents. First then, ac- 

 cording to the laws of statics, the air, which is less rarefied or expanded by 



