( 744 ) 
thermodynamic potential (whether it be in one sense or in the other) 
as the last, most fundamental quantity, which determines the internal 
condition of a body. As such we cannot take others than v and 7 
(if necessary of course w, y, etc.); that this is not only a subjective 
“point of view” appears perhaps most clearly from the study of the 
theory of capillarity, as van per Waats has given it. 
§ 4. From this follows naturally, that we must try to form 
an idea on the relation between the thermodynamic functions and 
these fundamental quantities, and this does not seem so very difficult 
to me just with regard to the thermodynamic potential. Let us only 
consider the following. Thermodynamics teach, that however composite 
the equilibrium may be, the total potential of every component must 
be the same in two phases which are in equilibrium; the kinetie 
theory, or in plain language, common sense that in all those cases 
equilibrium is only possible when an equal number of particles of 
each substance passes from the first phase into the second phase and 
vice versa. Now Van per Waats has shown *) that in the case of 
equilibrium of vapour and liquid, whether in a simple substance or 
a binary mixture, the two conditions are simply the same fact stated 
in different terms. It does not seem hazardous to me nor jumping 
to conclusions to conclude from this that these two conditions, which 
are always at the same time fulfilled or not fulfilled, also in other 
cases will agree in signification and that therefore the physical meaning 
of the thermodynamic potential *) of an homogeneous phase, on which 
no external forces act, is nothing but the number of particles which 
per second reach a wall as defined in the preceding communication 
§ 4 under 2, if this wall is thought in the midst of that homo- 
geneous phase. 
1) Verslagen Kon. Akad. Amsterdam (4) 3, 205 and Arch. Néerl. 30, 137. 
2) I choose purposely the words “that the physical meaning of etc.” and not 
“that the thermodynamic potential is equal to etc.” For the equality of the 
two quantities would require an “absolute” scale of thermodynamic potential. 
For from the equality of the conditions mentioned follows only: 
Mia SEN) EC en ee RE 
where Fis such a function, that Mg is a one-valued function of V and reversely 
N of Mp. This however, is not of material influence, for formula (1) expresses 
only, that we begin to count the thermodynamic potential from another point 
than the number of particles (which agrees with the fact that our thermodynamic 
potentials always include an undetermined constant) and that we make use of 
another unity when measuring one quantity than when measuring the other. 
There is therefore perfect concordance of our case ard that of the temperature 
measured e.g. according to Celsius and certainly nobody will object to the statement, 
also when he thinks of this temperature scale, that the physical meaning of the 
temperature is the mean vis viva of the centres of gravily of the molecules. 
