on the Cohesion of Fluids. 83 
equilibrium of the superficial forces, if the surface of the fluid 
make 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 particles 
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 by 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 being neutralised, as are 
equivalent 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 
ta be compared. We may therefore inquire into the conditions 
of equilibrium of the three forces acting on the angular par- 
ticles, one in the direction of the surface of the fluid only, a 
M 2 
