Chap. 2.] Swimming. 419 



proportion to the height of the -fluid ; the preffure, 

 therefore, which the body undergoes, is greater in 

 proportion to the depth into which- it is plunged. 

 Laftly, it has been proved, that when two fluids are 

 placed in equipoife, their refpective heights are in pro- 

 portion to their denfities ; and therefore bodies plunged 

 to an equal depth, are compreflcd according to the den- 

 fity of the refpective fluid. 



If a body is heavier than the fluid in which it is 

 immerfed, it is evident that ic will fink to the' bottom 

 by its fpecific gravity. If a body is lighter than the 

 fame bulk of the fluid into which it is plunged, a part 

 of it will fwirn, and the remaining part which is im- 

 merfed difplaces a quantity of fluid which weighs ex- 

 actly as much as the whole of the folid body *. 



if, 



* ' From what I have already explained, you muft neceffarily 

 have difcovcrcd the rationale tf Jinking and fwimming. You law 

 that when a body was bulk for bulk heavier than the fluid, by 

 bing immerJed it lofes only the weight of an equal bulk of the 

 fluid, and confequently the rejidual or remaining gravity of the 

 folid muft carry it dc.va to the bottom, or make it Jink. 



On the ether rnnd, if the folid has lefs weignt in the fame bulk 

 than the fluid, then it cannot by its weight difplace or raife up- 

 wards its whole bulk of the fluid, but only io much of it as is equal 

 to its own weight, and from this deficiency in weight it will be 

 only partly immerifc4 7 and will thereforeyov/w upon the upper part 

 of the fluid. 



Of all the animals, however, thrown into the water, man is the 

 moil helpiefs ; the brute creation receive the art of fwimming from 

 nature, while man can only acquire it by practice; the one efcapes 

 without danger, the other links to, the bottom. Some have af- 

 ferted, that this arifes from the different fenfibilities each have of 

 the danger ; the brute, unterrified at his iituation, ftruggles, while 

 his very fears fink the lord of the creation. 



But much better reafons may be affigned for this impotence of 



man .in water,- when compared to other animals; and one is, that 



he has actually more fpecific gravity, or contains more matter 



within the fame fujface than any other animal. Thutrunjc of the 



h e body 



