( 397 ) 
The integrated term is zero for the two limits and so we keep: 
A 7 De Aen & Py , ~ ie Pd fs (u) d 
ul Zum (u) du = 5 Ce u“ 7 (uw) | a di u° wu) du. 
0 0 0 
Also this integrated term is zero for the two limits. 
We .find therefore for the molecular pressure in the direction of 
the capillary layer: 
0 { i (u) du + Fo He fu (u) du 
N 4 2N dh2 y 
0 0 
or 
Cia OOO 
2 meel 28 
GIES dh? 
The pressure in consequence of the attraction has therefore an- 
other value in the direction of the capillary layer than in the direc- 
tion normal to this layer. In the direction of the capillary layer a 
surplus of molecular pressure will exist in consequence of the 
attraction. This surplus will amount to: 
cor dh : GO i ty 7 dy" 
Bn ge ce ONE ae Boe oo. 
or 
oe, dE Ca ( dy i 
— —og-—_+—|—}. 
Tie dae 2 \dh 
This surplus of pressure taken over a surface L to the bordering 
layer whose length in the direction of the capillary layer is 1 em. 
and whose breadth is equal to the thickness of the capillary layer, 
furnishes the value of the capillary tension : 
brenda OO Co (ee ) | 
DL EE EO Sa 
|; PE TT 
which integral is to be taken over the whole thickness of the 
capillary layer. 
We may make also another representation to ourselves of the 
capillary tension. Let us bear in mind that the thermal pressure 
Ea iia ok , 
oa Een point has the same value in all directions. If now 
in consequence of the molecular attraction the molecular pressure 
