88 ESSAYS AND OBSERVATIONS 



ad upon the water in one diredlion, ani 

 the water to readl upon the oars in the 

 oppofite diredlion, and to produce the 

 motion of the boat. Yet it is plain, that 

 the motion is intirely produced by the 

 rower, who, in fo far as he contributes 

 to the motion of the boat, employs the 

 oar as a lever of the fecond kind, where 

 the body to be moved, or the boat, is 

 placed betwixt the moving power and the 

 fulcrum. 



In the common account of the pro- 

 greffion of animals, whether it be of walk- 

 ing, flying, or fwimming, Borelli and all 

 other authors content themfelves with tel- 

 ling us, That the animal ads upon the 

 ground, air, or water, in one diredlion, 

 and that the reaclion of the medium car- 

 ries the animal forwards in an oppoti):e 

 diredion. This is at befl but too con- 

 clfe, not to call it a falfe theory : Seeing 

 it muft be manifeft that the medium, by 

 any readlion which takes place here, can 

 only confUme as much force as is impref- 

 fcd upon it, and is utterly incapa- 

 ble of producing any kind of motiouv 



The 



