( 448 ) 
that the abundance of blood capillaries around the organ seems to 
point to a connection with the regulation of the blood pressure in 
the cerebrum or the pressure in the ventricles, as VON CyoN main- 
tained to be the case for the entire hypophysis. Some experiments 
I made on the live embryos, seemed to confirm this conclusion. 
Kolozsvár, January 1902. 
Physics. — “Ternary systems.” (1st part). By Prof. J. D. VAN 
DER WAALS. 
THE PRINCIPLE OF CONTINUITY FOR A TERNARY SYSTEM. 
The equilibrium phenomena of a binary mixture at a given tem- 
perature may be illustrated geometrically by a surface, where volume 
and composition serve as abscissas and the free energy as ordinate. 
In the second part of my Continuity I have discussed the shape of 
such a surface and I have demonstrated what conclusions may be 
drawn from the properties of such a surface w =f (w,v). 
If we have a ternary system, for which two quantities z and y 
are required for the determination of the composition, then 
y= f(t 9 v) 
and so such a geometrical representation cannot be used. Though 
the geometrical representation is not necessary for the deduction of 
the conditions of equilibrium, and though it is not even possible to 
use it with increasing number of the components, yet for a binary 
mixture the great advantages of the graphical treatment have been 
sufficiently proved to continue employing it as long as we can. 
For a ternary system we find the means of effecting this in the 
properties of the ¢-function, according to the rule of equilibrium 
given by GrBBs, that at given 7 and p the substance arranges 
itself in such a way that the value of ¢ is as small as possible. 
At given Z and p the value of É is only dependent on z and y, 
and so the geometrical representation can again be used. 
If we think a ternary mixture as composed of 1 —#—y mole- 
cules of the first substance, of « molecules of the second substance 
and y molecules of the third substance in homogeneous phase, we 
obtain the value of ¢, as I have given it. (Verslag van 25 Sept. 
—— TT ET 
