HISTORY OF 



faster than its atmosphere at the equator ; so that 

 its motion, from west to east, gave the atmos- 

 phere an imaginary one from east to west ; and 

 thus an east wind was eternally seen to prevail. 

 Rejecting those arbitrary opinions, conceived 

 without force, and asserted without prooij Dr 

 Halley has given one more plausible ; which 

 seems to be the reigning system of the day. 



To conceive his opinion clearly, let us, for a 

 moment, suppose the whole surface of the earth 

 to be an ocean, and the air encompassing it on 

 every side without motion. Now it is evident, 

 that that part of the air which lies directly under 

 the beams of the sun will be rarefied ; and, if 

 the sun remained for ever in the same place, 

 there would be a great vacuity in the air, if I 

 may so express it, beneath the place where the 

 sun stood. The sun moving forward, from east 

 to west, this vacuity will follow too, and still be 

 made under it. But while it goes on to make 

 new vacuities, the air will rush in to fill up those 

 the sun has already made ; in other words, as it 

 is still travelling forward, the air will continu- 

 ally be rushing in behind, and pursue its mo- 

 tions from east to west. In this manner, the air 

 is put into motion by day, and by night the 

 parts continue to impel each other, till the next 

 return of the sun, that gives a new force to the 

 circulation. 



In this manner is explained the constant east 

 wind that is found blowing round the globe, near 

 the equator. But it is also known that, as we 

 recede from the equator on either side, we come 



