AttranloH and Repulfion ef footing Bodies, -tit^ 



IX. 



On the JLjfcHs of apparent yftiraifion, or Repulfton, between Bodies Jloat'tng upon or immerfed 



in Fluids. By M. MoNGE *. 



X HE motions of apparent attradion or repulfion which take place between floating bodies 

 on the furface of water or other fluids, are fufficiently remarkable to excite the curiofity of the 

 moft common obfervers. Men of confiderable eminence in the fciences have afcribed them 

 to dire£l forces a£ling between the bodies themfelves, and have overlooked the agency of the 

 fluid, which, indeed, performs the whole effe£l ; while others have pointed out the true caufe. 

 Our author is among the former, and I have no doubt but his clear and perfpicuous explana- 

 tion will be acceptable to the reader. 



If two light bodies, to which water is difpofed to adhere, be fufFered to float on the fur- 

 faCe of that fluid, and left to themfelves at the diftance of feveral inches from each other, 

 they will either remain at reft or obey the impulfe of the wind or other accidental forces; 

 but if they be placed at a fmall diftance from each other, fuch, for example, as half -an inch 

 or lefs, they will rufti together with an accelerated motion. A very perceptible force will be 

 required to feparate them, and whenever they are left to themfelves they will rufli together 

 as before. Or otherwife the -experiment may be made with a veffel containing water, 

 which, by its adhefion to the fides, forms a kind of eminence or ring all round : If in this 

 veflel a globe of cork be placed, this floating body will remain at reft while at a diftance 

 from the fides; but when brought within a certain fmall diftance of the fide, it will rufli 

 to it, and adhere in the fame manner as one of the fmall bodies in the former experiment. 



That thefe effedls are not produced by the immediate operation of an attratSive force in 

 the bodies themfelves, is proved by fufpending them to long flender ftrings ; in which fltua- 

 tion they are not found to be affe£ted by their vicinity to each other, or to the fides of the 

 veflel, provided they do not touch the fluid. Or in the laft experiment, if water be poured 

 in while the floating body lies in contact with the fide, it will be found that the apparent 

 attraiSion will continue no longer than till the furface is perfedtly level to the very border. 

 And when, by the continuation of pouring, the fluid becomes convex towards the fide, the 

 floating body will be fo far from adhering, that it will be repelled. 



Again, if two bodies be fufFered to float on the furface of water, one of which only is 

 capable of being wetted ; as for example, a ball of cork and another ball, of the fame ma- 

 terial, but blackened over by holding in a candle; thefe bodies will avoid each other, and 

 if urged together they will fly afunder as foon as they are left at liberty. If the ball with 

 the blackened furface be fufFered to float alone, it will be repelled by the fides of the velTel, 

 while the fluid remains elevated in contaiSt with thofe fides; but, on the contrary, it will be 

 attra£led, when, by the a£t of filling, the border of the fluid is rendered convex. 



* Abridged from the Memoirs of the Psrifian Academy for 1789, p. 506; 



Vol. III. — September 1799. ^^ "■ If 



