THE EARTH. 227 



CHAP. XX. 



OF WINDS, REGULAR AND IRREGULAR. 



Wind is a current of" air. Experimental philosophers produce 

 an artificial wind, by an instrument called an ceolipile. 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 man- 

 ner water is converted into a rushing air j which, if caught as it 

 goes out, and left to cool, is again quickly converted into its for- 

 mer element. Besides this, as was mentioned in the former 

 chapter, almost every substance contains some portions 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 escap- 

 Mig 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 admis- 

 sion into wine, or any fermented liquor : and an easier still into 

 spirits of wine. Some salts suck up the air in such quantities, 

 that they are made sensibly heavier thereby, and often are melted 

 by its moisture. In this manner, most bodies being found either 

 j'upable of receiving or affording it, we are not to be surprised 

 at those streams of air that are continually fleeting round the 

 globe. — ]VIiner>Js, vegetables, and animals, contribute to increase 

 the current ; and are sending off their constant sujjplies. These, 

 as they are differently affected by cold or heat, by mixture or 

 putrefaction, all yield different quantities of air at different times; 

 and tlie loudest tempests, and most rapid whirlwinds, are formed 

 from their united contributions. 



The siin is the principal instrument in rarefying the juices of 

 ]jjaiits, so as to give an escape to their imprisoned air ; it is also 

 equally operative in promoting the putrefaction of animal*. 

 Mineral exhalations are more frequently raised by subterranean 

 heat The moon, the other planets, the seasons, are all com- 

 bined in producing these effects in a smaller degree. Moun- 



