(4 
Physics... — “Statistical Hlectro-mechanics.“. By Dr. J. D. vaN DER 
Waars Jr. (Communicated by Prof. vaN DER WAALS). 
Prof. Gipss has newly published a treatise entitled “Elementary 
principles in statistical mechanics”, in which he communicates some 
considerations, belonging to a science, which he calls “Statistical 
mechanics,” and of which he states that “on account of the 
elegance and simplicity of its principles” it is eminently worthy 
that the laws to which it is subjected, are studied. The laws relate 
to the behaviour of a great number of systems, whose motions are 
mutually independent. These systems quite agree with one another 
as to their nature, and only differ in so far, that the integration 
constants of the differential equations of motion have different values, 
or, what comes to the same, that the values of the generalized coör- 
dinates and of the generalized velocities at an arbitrary moment 
(e.g. at the moment ¢= 0) differ for different systems. The laws, 
which hold for such ensembles of systems have a very general 
character, as GiBBs shows; yet in their application they are confined 
to systems, consisting exclusively of ordinary matter. Now the 
question arises whether such like considerations might be applied 
to electro-magnetic systems, and whether in doing so we might 
extend our very limited knowledge of the phenomena of radiation in 
connection with the laws of thermodynamics. 
We cannot deny however that we must not expect foo much from 
these considerations. The greater part of the theses deduced by GrBBs 
are exclusively or principally applicable to ensembles of systems which 
he calls canonical and which have such an important phace in his 
considerations, because they represent the simplest law possible of the 
distribution ot the systems over the different “phases” *). Mathematical 
simplicity, however, is not a trustworthy criterion, when we want 
to investigate, what is actually to be found in nature. For our 
mathematical representation e.g. the simplest motion, a vibrating 
string can perform, is an harmonic motion, yet we should be utterly 
mistaken if we should assume, that every vibrating string would 
execute such a motion. Perhaps we run the risk of making similar 
mistakes if we assume, that all systems in nature will follow the 
laws which we have deduced on the supposition of a canonical 
distribution of the systems of an ensemble. 
It is true that Gress shows in his chapters XI—XIII that the cano- 
1) Two systems are considered to be in the same phase when they are to be 
found in the samé element of extension in phase. 
