on Floating Bodies. 477 



understand the subject, I beg to be allowed to trespass again 

 on your indulgence. 



I am persuaded that no person who has investigated the 

 subject, will deny that all water in motion descends an in- 

 clined plane, and that bodies floating in it are actually de- 

 scending an inclined plane also, being influenced by two- 

 causes in their progress; first, by the motion communicated 

 to them by the fluid in which they float ; and secondly, by 

 their own weight arising from the inherent property of gra- 

 vity, which, whether the body be more or less specifically 

 heavy, is immutable, and peeuiiar to all matter. — In vacuo, 

 as every one knows, a feather and a piece of gold will de- 

 scend with equal velocity, and pass through equal spaces in 

 equal times; but in air or water, the progress of bodies spe- 

 cifically different, will vary according to their specific gra- 

 vity ; the lighter body, possessing. less power to overcome 

 opposition, must of course be slower in its progress. — If 

 the wood and metal balls, which [ mentioned, were let fall 

 in vacuo, or if they were mathematically polished, and passed 

 down an inclined plane so polished and placed \n vacuo, they 

 would both descend with the same velocity; but in open air, 

 and on a rough surface, the heaviest body being possessed 

 of greater power, arising from a greater quantity of matter, 

 viz. from greater specific gravity, it will have the greater 

 power in overcoming opposition, and will pass on with the 

 more rapid motion ; but still in both bodies the principle of 

 gravity is the same. 



Mr. B. says that 1 am mistaken in making a comparison 

 between balls of different weights rolling down an inclined 

 plane, and barges or beams of different weights floating 

 down a running stream : that is, as I understand him, he 

 does not like the comparison, and he says the balls move 

 through a medium perfectly at rest, but the barges, &c, 

 through a medium in motion. — I beg leave to observe to 

 Mr. B., that the air or atmosphere is never perfectly at rest, 

 except when all its particles are in equilibrio, which is sel- 

 dom the case, and never generally so. Balls may meet cur- 

 rents of air, or may overtake air moving slower than them- 

 selves: in either case, their motion must bq retarded more or 



less, 



