751 
to BonrzMaNn’s theorem is connected with the probability that, in 
wv system consisting of a solid and a gaseous phase, a greater or a 
smaller part belongs to the latter. The circumstance that, in con- 
sidering this latter probability, we must attend to the difference 
in potential energy of the two phases cannot but increase our 
doubt, for neither in the determination of S" nor in the determi- 
nation of S in the above mentioned way we have had to speak 
of this difference. If, as we should expect, the difference S—S" 
depended to a considerable extent on the relative values of the 
potential energy, we might still put the entropy S"” —O for 7’— 0, 
but it would no longer be possible to determine the constant « 
which occurs in formula (1) for the gaseous state by considering 
only the phenomena in the gas, as is done in the theories discussed 
here. We ought rather to derive it from an examination of the 
equilibrium between the two phases. 
I think we may conclude from what precedes that, though the 
value found for w, if it be not quite accidental, pleads in favour 
of the application of the theory of quanta to the problem of vapor- 
isation, yet the way in which this application has been made 
requires further explanation and justification. 
Physics. — “On Hamitron’s principle in EiNsrriN’s theory of gra- 
vitation”. By H. A. Lorentz. 
(Communicated in the meeting of January 30, 1915). 
The discussion of some parts of EinsrriN’s theory of gravitation ') 
may perhaps gain in simplicity and clearness, if we base it on a 
principle similar to that of Hamitton, so much so indeed that 
HAMILTON’s name may properly be connected with it. Now that 
we are in possession of EINsreiN’s theory we can easily find how 
this variation principle must be formulated for systems of different 
nature and also for the gravitation field itself. 
Motion of a material point. 
§ 1. Let a material point move under the influence of a force 
with the components AKA, Let us vary every position «x,y,z 
1) EINSTEIN u. GROSSMANN, Entwurf einer verallgemeinerten Relativitätstheorie 
und einer Theorie der Gravitation. Zeitschr. f. Math. u. Phys. 62, (1914), p. 225. 
EINSTEIN, Die formale Grundlage der allgemeinen Relativitätstheorie, Sitz. Ber. 
Akad. Berlin, 1914, p. 1030. 
