( 526 ) 
a carbon-source, rapidly lead to the accumulation of strong ureum- 
splitting bacteria forming spores and the urobacillus jakschit forming 
no spores. 
5. The irisating of culture-plates and the “irisphenomenon” on the 
yeast-water-gelatineplate are the consequence of the precipitation of 
calciumphosphate, whilst calciumcarbonate formed at the same time 
plays a subordinate part in it. 
At the end of this investigation I beg to express my sincere thanks 
to Professor M. W. Brwrinck for advising and “supporting me in 
these experiments wherever and whenever he could. 
Physics. — “Statistical Theory of Capillarity.” By Dr. L. 5. ORNSTEIN. 
(Communicated by Prof. H. A. Lorentz). 
(Communicated in the meeting of December 24 1903). 
In a paper *) published in 1893 VAN DER Waars has developed a 
theory of capillarity, which leads to results agreeing sufficiently with 
observation, as has been shown by the experiments of Dr. E. O. DE 
VRIES. 
The methods used in the above mentioned paper have been repro- 
duced with only a slight change in the lectures of van per WaaLs 
recently published by Prof. Pr. KOHNSTAMM. 
Both in the paper and in the treatise the hypothesis *) is introduced, 
that the entropy of an element of volume is a function only of the 
number of molecules it contains and of that of their collisions. 
By the statistical method of G1BBs we can deduce the condition of 
equilibrium for the capillary layer without using a hypothesis of this 
kind and we can easily show that it must be true when certain condi- 
tions are fulfilled. This is the object of the present paper in which 
I shall also determine some quantities that play a part in the theory 
of capillary action. 
§ 1. Let us suppose that m spherical molecules of diameter o, per- 
fectly rigid and elastic, are enclosed in a vertical cylinder of height 
Z, and of unit of horizontal section, closed at the top and the 
bottom by horizontal walls. Let the axis of 2 be drawn upward and 
let us further suppose that the molecules exert attractive forces on 
Dele. Vier Day VAALS, Thermodynamische theorie der capillariteit in de onder- 
stelling van continue dichtheidsverandering. Verh. d. K. A. v. W. Deel I. 8. 1893. 
2) Compare |. c‚ p. 16. 
