( 804 ) 
if we could enclose the system between absolutely reflecting walls 
in the new state, and if we could thus maintain the same state of 
radiation, but without absorption of new energy. Such a system 
would no longer respond to the laws of thermodynamics, even if 
we included among them the thermodynamics of radiation, in the 
same way as we found that for the “osmotie temperature” the ther- 
modynamie law of constancy of the thermodynamic potential is not 
fulfilled. Our experimental and theoretical knowledge is not sufficiently 
advanced to decide whether the photo- and electrochemical “equilibria” 
belong to this or the preceding category *). 
Physics. — “Some remarks on the mechanical foundation of thermo- 
dynamics.” 1. By Dr. L. 5. ORNSTEIN. (Communicated by Prof. 
H. A. Lorentz). 
(Communicated in the meeting of December 24, 1910). 
In order to deduce the second law of thermodynamics the theory 
of ensembles of systems is often used. This theory has been largely 
discussed by J. W. Gras in his well-known Elementary Principles 
of Statistical Mechanics. In his book two kinds of ensembles, the 
canonical and the microcanonical, come to the fore. The latter kind of 
ensembles has been used by Dr. Paur Hertz who held some views 
which give me occasion for a few remarks *). 
§ 1. In the beginning of his paper Dr. Hertz explains that it is 
rational to use for the study of the phenomena shown in a given 
system the ensemble of states taken by that system when left to 
itself. Such an ensemble is usually termed a time-ensemble. As 
the observed phenomena must be considered as the result of many 
phases adopted by the system during the time of observation, we 
have every reason to presume, that our observation teaches us 
“something of the mean value in the time-ensemble. By using the 
terminology of poly-dimensional geometry we can put the following 
1) We will point out that it is sometimes still impossibie to assign a place 
in this classification to a phenomenon in the department of catalysis It is e.g. 
difficult to explain in what connection with the mentioned casés the fact is 
that the thermodynamic potential of perfectly dry solid NH,CI is so considerably 
modified by the addition of the slightest trace of moisture, as appears from the totally 
modified partial vapour pressure of the NH,Cl molecules. Perhaps this case will 
appear to be an example of 2. 
2) Ann. der Phys. Bd. 30, p. 236, 1910. 
