bii'ween Bodies Jtoatitjg on Water, ^c. 271 



coiifiderable extent, very eafily obfervable, by attending to the refledion of a ftrait body, fuch 

 as the frame of a window from the funace. In fig. 2, where the bodies are brought nearer, 

 the cavities do not comnuinicate, and, confequently, the reaftion of the water all round each 

 ball is the fame, and they have no tendency to move in one' direction more than another. 

 But when they are brought ftiil nearer, as in fig. 3, the efFeft of the repulfive powers of 

 both deprefles the furfacc between them, and the rea<5iion of the fluid becomes lefs in propor- 

 tion to its diminiftied height. The confequence is, that the bodies move towards each 

 other from the external preflUre or readion which continues undiminiflied. 



When two bodies of this kind are fubmerged, as in fig. 4, the fluid will be difplaced from 

 between them, if the air can have accefs, and the bodies will be prefled together by the force 

 on the oppofite parts. If the air cannot enter between them, the liquid will not be excluded 

 unlefs the force of repulfion be equal to that of the preflure of the atmofphere; but the ten- 

 dency to feparation is productive of the fame effe£t. Philofophers- who operate with the 

 pneumatic apparatus over mercury, have frequent occafions to notice this fa£t, when they 

 plunge their hands in that denfe fluid. For, upon attempting to feparate the fingers in this 

 fituation, a refiftance is felt, which does not arife from any difficulty of moving the fluid, but 

 fimply from this caufe. It is a perception as if the fingers attraiiied each other, and is not 

 felt except when they are neai- each other. 



Fig. 5 reprefents two bodies. A' and A, in the fituation of the third general hSt or 

 law. One of them being wetted has a mafs of the fluid hanging round it, and the other 

 forms a furrounding cavity by its repulfion. At the diftance here exprcfTed the bodies do 

 not afFeft each other. In fig. 6 the general furface B is ftill unaltered : but at fig. 7 the 

 curves interfere. The body A may be confidered as if on a moveable inclined plane of 

 water, down which it will Aide, while the plane itfelf, with the body A', to which it is 

 attached, will be moved in the contrary diredion. The bodies will feem to repel each 

 other. 



As this eiFe£t alfo takes place beneath the fluid, that is to fay, that the body which is dif- 

 pofed to be wetted, or which attrafts the fluid, will exert a kind of repulfion upon any other 

 body which repels the fluid, our author infers, that it may be confidered as a pretty accu- 

 rate reprefentation of what happens in chemical precipitations. This, however, feems 

 fcarcely to apply to the cafe, as both principles in chemical folution appear to have an at- 

 traftion to the folvent. 



The firft law or general faft, where apparent attraction is produced in two bodies capable 

 of being wetted, employs a large portion of his refearch. If (fig. 8) a flip of glafs be fufpended 

 at the extremity of a thread fixed to the point K, fo that its lower end (hall be plunged in 

 the water, reprefented by MN, it is well known that the fluid will attach itfelf to the fides of 

 the glafs, fo as to form two concave furfaces, EDC, HGF, higher than the common furface. 

 As we are not acquainted with the laws of the force by which thefe effefls are produced, 

 and no obfervations have been made on the dimenfions of the curve itfelf, little can be faid 



N n 2 concerning 



