THE EARTH. 



99' 



CHAPTER XX. 



OF WINDS, IRREGULAR AND REGULAR. 



WIND is a current of air. Experimental 

 philosophers produce an artificial wind, by 

 an instrument called an eolipile. This is 

 nothing more than a hollow copper ball, with 

 a long pipe ; a tea-kettle might be readily 

 made into one, if it were entirely closed at 

 the lid, and the spout left open ; through this 

 spout it is to be filled with water, and then 

 set upon the fire, by which means it produces 

 a violent blast, like wind, which continues 

 while there is any water remaining in the 

 instrument. In this manner water is con- 

 verted into a rushing air; which, if caught 

 as it goes out, and left to cool, is again quick- 

 ly converted into its former element. Besides 

 this, as was mentioned in the former chapter, 

 almost every substance contains some por- 

 tions of air. Vegetables, or the bodies of 

 animals left to putrefy, produce it in a very 

 copious manner. But it is not only seen thus 

 escaping from bodies, but it may be very 

 easily made to enter into them. A quantity 

 of air may be compressed into water, so as 

 to be intimately blended with it. It finds a 

 much easier admission into wine, or any fer- 

 mented liquor; and an easier still, into spirits 

 of wine. Some salts suck up the air in such 

 quantities, that they are made sensibly hea- 

 vier thereby, and often are melted by its 

 moisture. In this manner, most bodies, being 

 found either capable of receiving or affording 

 it, we are not to be surprised at those streams 

 of air that are continually fleeting round the 

 globe. Minerals, vegetables, and animals, 

 contribute to increase the current; and are 

 sending ofF their constant supplies. These, 

 as they are differently affected by cold or 

 hoat, by mixture or putrefaction, all yield 

 different quantities of air at different times ; 

 and the loudest tempests, and most rapid 

 whirlwinds, are formed from their united 

 contributions. 



The sun is the principal instrument in 

 rarefying the juices of plants, so as to give 

 an escape to their imprisoned air ; it is also 



equally operative in promoting the putrefac- 

 tion of animals. Mineral exhalations are 

 more frequently raised by subterranean heat. 

 The moon, the other planets, the seasons, 

 are all combined in producing these effects 

 in a smaller degree. Mountains give a direc- 

 tion to the courses of the air. Fires carry 

 a current of air along their body. Night and 

 day alternately chill and warm the earth, and 

 produce an alternate current of its vapours. 

 These, and many other causes, may be as- 

 signed for the variety and the activity of the 

 winds, their continual change, and uncertain 

 duration. 



With us on land, as the wind proceeds from 

 so many causes, and meets such a variety of 

 obstacles, there can be but little hopes of 

 everbringing its motions to conform to theory; 

 or of foretelling how it may blow a minute to 

 come. The great Bacon, indeed, was of 

 opinion, that by a close and regular history 

 of the winds, continued for a number of ages 

 together, and the particulars of each observa- 

 tion reduced to general maxims, we might at 

 last come to understand the variations of this 

 capricious element; and that we could fore- 

 tell the certainty of a wind, with as much 

 ease as we now foretell the return of an 

 eclipse. Indeed, his own beginnings in this 

 arduous undertaking, seem to speak the pos- 

 sibility of its success ; but, unhappily for man- 

 kind, this investigation is the work of ages, 

 and we want a Bacon to direct the process. 



To be able, therefore, with any plausibility, 

 to account for the variations of the wind upon 

 land, is not to be at present expected ; and 

 to understand any thing of their nature, we 

 must have recourse to those places where 

 they are more permanent and steady. This 

 uniformity and steadiness we are chiefly to 

 expect upon the ocean. There, where there 

 is no variety of substances to furnish the air 

 with various and inconstant supplies ; where 

 there are no mountains to direct the course 

 of its current, but where all is extensively 



