87© Apparent Powers of Attratiion and Repulfion • 



If thefe balls be alfo fufpended by ftrings, it will be found that the efFe£ls do not arife 

 from any immediate attraftive or repulfive force. 



Laftly, If two bodies be fuffered to float on the furface of the liquid, neither of which are 

 capable of being wetted, an apparent attradion will take place between them ; they will be 

 attrafted by the fides of the veflel when the fluid is convex, or repelled when its termina- 

 tion is concave. 



Thefe circumftances maybe fummed up by obferving, i.That two bodies fufceptible 

 of being wetted will appear to attraft each other when floating on the furface of water. 

 2. When two bodies, not capable of being wetted, are either floated or immerfed in a fluid, 

 they will ftill have the fame apparent attradlioni and, 3. When the two bodies, either immerfed 

 or floating, are one of them capable of being wetted, and the other not, they will exert 

 an aftion produdlive of the fame effedl as if a mutual repulfion were exerted between 

 them. 



As the prejudice the two drops of water mutually attradt each otlier is generally re- 

 ceived, the author gives a number of inftances which tend to overthrow it. He obferves, 

 that two fuch drops are very far from exhibiting any attradtion; infomuch that they may even 

 in a dry ftate of the air be ftruck againft each other, fo as to alter their figure without uniting 

 together. Thefe feparate drops may be (hewn to advantage by caufing the fluid to fall in 

 drops through a fmall tube, from the height of a few lines, upon the furface of a mafs of the 

 fame fluid. The tube muft be flightly inclined, in order that the drop may run away in the 

 horizontal direction. Spirit of wine is better adapted to this experiment than water. The 

 fpherical drops move along the furface with the utmofl: eafe and rapidity ; fometimes ftriking 

 each other fo as to change their figure without uniting, and it is a confiderable time before 

 they confound themfelves with the general mafs. M. M. thinks the evaporability of the 

 fpirit and the mutual attraction of its parts are the caufes why this fliiid exhibits the pheno- 

 menon in a more fl;riking manner than water; in which laft fluid it is, however, often k^n. 

 when agitated by the dafliing of oars, the f 11 of violent rain, and the like. It is very eafy 

 to diftinguifh thefe folid globules from the veficles or hemifpherical bubbles filled with air» 

 becaufe the former are much more moveable. 



This appearance of drops rolling on the furface of a liquid is more durable the fmaller 

 the drops. When any heated liquor of a brown or dark colour, coffee for example, is ex- 

 pofed to the air, the ftratum of heated air in contaS with the furface becomes loaded with 

 vapour, and rifes to an elevation, where it cools and depofits part of the water in the form 

 of a fmoke or vapour, which condenfes into drops that fall on the furface of the coloured 

 liquid, and conftitute a kind of fcum. Thele globules being fmall retain their fituation 

 a long time, and are very diftinguifhable from bubbles by their great mobility, as the flightefl 

 breath of wind is fufBcient to difperfe and arrange them along the fides of the vefFel. 



Our author adopts the explanation of Mariotte for the fecond general fail: or law, which 

 is, that floating bodies not capable of being wetted will apparently attradt each other. In 

 fig I. plate XI. the globes A and A' float upon the fluid, in which each makes a cavity of 



confiderable 



