'184 STUDIES OF NATL-RE. 



I am not taking for granted, without any foun- 

 dation, the exiRence of thefe counter-currents, or 

 vortices^ after the manner of Syflem-makers, who 

 create new caufes, in proportion as Nature prefents 

 them with new effedts. Thefe vortices are hydrau- 

 lic re-aflions, the laws of which Geometry ex- 

 plains, and the reality of which is completely afcer- 

 tained by experience. If you look at a fmall run- 

 ning brook, you will frequently fee ftravvs floating 

 along the brink, and carried upward in a direélion 

 oppofite to the general current of the ftream ; and 

 on arriving at the points, where the counter-cur- 

 rents crofs the general, you obferve them agitated 

 by thefe two oppoled powers turning and fpinning 

 round a confiderable time, till they are at lad car- 

 ried down the general current. 



Thefe counter-currents are fiill more percep- 

 tible, when fuch a rivulet flows through a bafon 

 which has itfelf no flux ; for the re-adion is, in 

 that cafe, fo confiderable round the whole circum- 

 ference of the bafon, that the counter-currents 

 carry about all bodies floating in i*;, to the very 

 place where the rivulet difengages itfelf 



Thefe lateral counter-currents are fo perceptible 

 on the banks of rivers, that the watermen fre- 

 quently take the advantage of them, to make their 

 way in the diredion oppofite to the general courfe. 



They 



I 

 I 



