( 733 ) 
For what is the case? The behaviour of liquids is entirely dominated 
by the occurrence of the quantities « and 5 in the equation of 
state. Only matter in dilute solution seems to emancipate itself 
from it, according to the law of Var ‘r Horr, where neither 
the « nor the 5 occurs. This fact calls for an explanation. 
Now it is not difficult to understand, why the @ can disappear 
here; the membrane is bonnded on one side by the solution, on 
the other side by the pure solvent. If we now think it thin com- 
pared to the extent of the sphere of action, then it is clear that at 
the membrane the force = which works towards the solution, is 
ve 
a 
in first approximation neutralized by the force —— towards the other 
ty? 
side. It is more difficult to see why also the 4 vanishes, i.e. why 
the molecules of the dissolved substance seem to move as through a 
vacuum, instead of through a space, which is occupied for a very 
great part by the molecules of the solvent. 
Just on this most important point Prof. LoreNtz’s paper leaves us 
in the dark, for so far as I have been able to see. And it seems to 
me beyond doubt, that in the first place this is due to an inaccurate 
interpretation of the term “kinetic pressure”. According to Prof. 
Lorentz it is always equal to */, of the kinetic energy of the centres 
of gravity of the molecules which are found in the unity of volume. 
It is therefore independent of the volume of those molecules. Now 
this would only be a question of nomenclature, if not that kinetic 
pressure was also defined as the quantity of motion, carried through 
the unity of surface in the unity of time by the motion of the 
molecules; and that this quantity is dependent on the number 
of collisions and so on the volume of the molecules does not seem 
open to doubt to me after KorreweEG’s proof *). In agreement with 
this the kinetic pressure is represented in the equation of state by 
MRT/v—b. In consequence of his definition Lorwxrz replaces this 
*) Zsch. phys. Ch. 7, 37 and Arch. Néerl. 25, 107. 
2) Zsch. phys. Ch. 6, 474 and 7, 88. 
3) Verslagen Kon. Ak. Amst. (2) 10, 363 and Arch. Néerl. 12, 254. Compare 
also the simpler, perhaps even more convincing proof for one dimension in Nature 
44, 152. As the attentive reader will notice Prof Lonenrz’s proof (1. e. 59) does 
not take into account the collisions and the fact ensuing from them, that a quantity 
of motion skips a distance or moves with infinite velocity for a moment. And 
the admission of the validity of Korrewec’s reasoning appears, as it seems lo me, 
already from the fact, that Prof. Lorentz has to assume for the solid bodies intro- 
duced by him, that they are immovable (Il. c. 40) or of infinite mass (l. c. 42) 
which comes to the same thing in this case. 
50* 
