426 Dr. G. Bakker on the 
function of v=~, so is the point E of the curve, where the 
ordinate has its maximum value, exactly the point of the 
theoretical isotherm for which fi = /i l9 or : 
surface DAGM = surface LEGM. 
When, namely, fi=f*i, the equation 
V+2a / o=jot 1 — fi 
gives V= —2ap, 
and the equation (18 a) becomes 
p = 0-ap\ 
Now, we have for the theoretical isotherm: 
p = 0—ap 2 . 
Hence P—P» 
§ 4. The capillary layer, which envelops a spherical 
drop of liquid. 
Hitherto we have considered a bubble of vapour, which 
was enveloped by liquid. Let us now consider a spherical 
drop of liquid enveloped by the vapour. The capillary layer, 
which envelops the liquid, is in this case convex on the side oj 
the vapour, and the differential equation for the potential of 
the forces of cohesion is, instead of the equation (10 a) 
above : 
2 <PY 2X 2 dV _ 
while the difference between p v and p T is found by the aid 
of the equation (13) in changing R into — R. Hence 
2 X 2 C*/dV\*, 7 2H 
^-^=U2a} 1 {dh) dh =^' ' * < 19 > 
In the same manner as above, we find that the thermodyn. 
potential has the same value in the homogeneous phase of 
the liquid as in that of the vapour. If A and C in fig. G 
are the points of the theoretical isotherm, which correspond 
respectively with the volumes of the liquid and vapour, 
which limits the capillary layer, we must have thus: 
surface DASQ=sur£ace SCKH. 
