568 MOSSOTTI ON CAPILLARY PHA:NOMENA,. 
face, since we suppose the plane to have no action on the fluid.. 
If, on the contrary, the plane exerts a small action on the fluid, 
the attraction along the liquid surface contiguous to the plane 
will be less, for in that part the fluid will be less rarefied, and 
we can easily see that it will not detach itself from the plane 
until the resolved part of its attraction, acting in the vertical at 
the free surface, shall be equal to the attraction along the surface 
touching the plane. These two forces will then counteract each 
other, and the free surface will join that which is-in contact with 
the plane at an angle which, as we shall see presently, remains 
constant for the same fluid, whatever be the solid substance 
employed. 
What takes place on one side near the surface of one of 
the two planes must happen equally at the opposite side near 
the other plane. hus the cylindrical free surface of the fluid 
will be as it were united at its extremities to the two plane sur- 
faces in contact with the solid planes; and since a force of con- 
traction exists along them and at their points of conjunction with 
the free surface, this surface will be drawn downwards and will 
compress the fluid beneath ; and if the two planes are very near, 
the effect produced will be very sensible, and the liquid will 
descend between the two planes, below the level of the external 
liquid, until the above-mentioned forces of attraction be counter- 
acted by the increase of pressure which the fluid, at a higher 
level without the planes, exercises in consequence of its gravity. 
In the second case, the attraction of the solid planes on the 
fluid in contact with them being greater than that of the fluid 
on itself, the fluid in contact with the planes will be compressed 
and will rise along the surface of the planes, which will thus be 
covered with a fluid sheet, which on either side will be united 
below with the free surface of the fluid. The two parts will 
together form a continuous free surface, concave externally, tan- 
gent on either side to the planes, and along which there will be 
a force of attraction. This force at the two opposite extremities 
will draw the concave surface of the liquid upwards in a vertical 
direction, and will tend to detach it from the liquid underneath ; 
the contiguous particles at the lower points will therefore become 
slightly more separated from one another, the adjacent fluid will 
hence acquire a force of tension of its own, and will follow the 
ascending motion of the free surface. When the weight of the 
