( 390 ) 
Therefore we shall determine the molecular pressure in a point 4 
of the capillary layer: 
a. in the direction normal to the surface of the liquid; 
4. in the direction parallel to the surface. 
a. Through A we lay a plane parallel to the surface of the 
liquid. The force with which the layer of a thickness du, parallel 
to the separating layer, at a distance « below the plane laid through 
A, attracts the unity of mass /, h;¢M above this plane, is: 
— dw (u + hj), 
on the supposition that the examined layer has the unity of density. 
The density in a 
layer parallel to the 
surface of the liquid 
is the same every- 
where. We give there- 
fore, the density as a 
function of the dis- 
tance from the plane 
laid through A, If 
we call the normal 4 and take as positive direction that one turned 
towards the vapour phasis, so that 4 = 0 is situated in the homo- 
geneous liquid phasis, the density of the layer with a thickness 
du will be: 
Fig. I 
do u2 d° 0 
ou + 
etc. 
dh is 2 dh? 
do dg 
where g, OEE have the values which these quantities have in 
dh an” 
point A, For all layers below the plane through it, the attraction is: 
i; ( do u? a Tee 
Eten 0 — — — 1 J . 
3 . % dh 1.2 dh? a 1 
Let us imagine in / not the unity of mass, but let us consider 
there a volume-element with a thickness of dh, and for the sake of 
simplicity with a base of 1 em? instead of do, The density of this 
volume-element being: 
