£8 



COHESION OF FLUIDS. 



Cohesive jit- 

 traction of 

 solids and 

 fluids. 



Vn. Cohes'ne Attraction of Solids arid Fluids. 

 When the attraction of the particles of a fluid for a solid is 

 less than their attraction for each other, there will be an 

 equilibrium of the superficial forces, if the surface of the fluid 

 iHcikc with that of the solid a certain angle, the versed sine of 

 which is to the diameter, as the mutual attraction of the fluid 

 and solid particles is to the attraction of the particles of the 

 fluid among each other. For, when the fluid is surrounded 

 by a vacuum or by a gas, the cohesion of its superficial parti- 

 cles acts with full force in producing a pressure ; but when it 

 is any where in contact with a solid substance of the same 

 attractive power with itself, the effects of this action must be as 

 much destroyed as if it were an internal portion of the fluid. 

 Thus, if we imagined a cube of water to have one of its halves 

 congealed, without any other alteration of its properties, it is 

 evident that its form and the equilibrium of the cohesive forces 

 would remain undisturbed : the tendency of the new angular 

 surface of the fluid water to contract would therefore be com- 

 pletely destroyed hy the contact of a solid of equal attractive 

 force. If the solid were of smaller attractive force, the ten- 

 dency to contract would only be proportionate to the difference 

 of the attractive forces or densities, the effect of as many of the 

 attractive particles of the fluid beingneutralized, as are equiva- 

 lent to a solid of a like density or attractive power. For a 

 similar reason, the tendency of a fluid to contract the sum of 

 the surfaces of itself and a contiguous solid, will be simply as 

 the density of the solid, or as the mutual attractive force of the 

 solid and fluid. And it is indifferent whether we consider the 

 pressure produced by these supposed superficial tensions, or 

 the force acting in the direction of the surfaces to be compared"! 



(The conchision in ovr next.) 



