1334 
which if we also introduce & == '/, osl, becomes quite identical with 
our formula (7). 
And this is not surprising. For according to CUNNINGHAM the second 
term will preponderate in equation (8), when only sliding friction 
occurs, i.e. when the motion of the surrounding molecules has 
become quite independent of the suspended particle. On such a state, 
we have, however, also founded our considerations. At bottom 
CUNNINGHAM’S Suppositions entirely agree with those of VON SMOLCCHOWSKI. 
l 
According to both writers it will depend on the value of — whether 
a 
: 1 1 Pe 
for A? the formula with — or that with — isto be used. Our opinion 
a a 
is opposed to this. According to us the formula with ' is always 
ay 
the correct one. 
In order to prevent misunderstanding we will state that we by 
no means intend to deny the validity of the formulae given by 
Stokes and CUNNINGHAM for the friction of a small particle moving 
through a resisting medium. We are only of opinion that the appli- 
cation of the formulae should be confined to non-reversible processes, 
in which friction actually appears. When a particle falls under the 
influence of gravitation or when it is electrically charged and moves 
under the influence of electric forces, we think that the said formulae 
will give the true value for the friction. But in case of Brownian 
movement, which is a phenomenon of thermal equilibrium, we think 
we have to assume independence of the velocities of the different 
particles on the ground of statistical mechanics, which, as we demon- 
strated, leads to a value of A? proportional to = 
Chemistry. — “The P,X-jigures of Unary Systems, According to 
the Theory of Allotropy.” By Prof. A. Smits. (Communicated 
by Prof. J. D. van per Waats). 
(Communicated in the meeting of January 29, 1916.) 
1. Introduction. 
I will begin this communication by reminding the readers that 
the theory of allotropy is based on the hypothesis that in case of 
allotropy for an element or a compound every phase is complex, or 
in other words, consists of at least two kinds of molecules, between 
which internal equilibrium prevails in case of unary behaviour. *) 
') The words different kinds of molecules are to understand in a general sense. 
lons also belong to the different kind of molecules. An internal equilibrium is a 
equilibrium of a unary system. 
