Physics. — “The osmotic pressure, regarded as a capillary pheno- 
menon’”. By H. Hursnor. (Communicated by Prof. H. A. Lorentz). 
(Communicated at the meeting of March 27, 1920). 
In this paper an attempt will be made to give an explanation of the 
osmotic pressure by regarding this pressure as the consequence of 
capillary actions. Though some difficulties remain, in my opinion 
a trial in this direction might be made. In a former communication 
(these Proceedings January 1900) the surface tension has been defined. 
To that end we supposed at a point of the passage layer fluid- 
vapour the influence of the attraction in different directions to have 
different values. Now we shall base our considerations on the same 
suppositions. For a plane in the direction of the passage layer p, is 
the whole force per unit of surface (pressure) exerted by the matter 
on one side of the plane on that on the other side. It consists of 
the attraction q, and what may be called the thermic pressure 1, 
so that 
Di a! EE o. 
For a surface element perpendicular to the passage layer we can 
also speak of the total force exerted by the part of the system on 
one side on the part on the other side. Let us call this p, and let 
us write g, for the attraction between the two parts and & for the 
thermic pressure. Then we have: 
ben 
Instead of the attraction g, and g, we may also consider the 
molecular pressure J/,’ and M,’; q, = M,’ and q, = M,’; in homo- 
a 
geneous phases g—= M’ =ao?= —. The thermic pressure 9 = 
v 
MRT 
a will be supposed to have in all directions a value equal to 
that in a homogeneous phase of the density at the point in question. 
Pao = Ps +} M, =p+M=d. 
The index 1 refers to the direction perpendicular to the passage 
layer, the index 2 to a direction in this layer; as to gravity we 
assume that it only causes the layers to be horizontal; the height 
h is measured upward perpendicular to the passage layer. Differen- 
