( 765 ) 
genus, directly intermediate between Polyporandra Bucc. and Nat- 
siatum BucHaN. Because the material is so incomplete, I have, however, 
thought it advisable to refrain even from proposing a new sub-genus 
and to assign to this species a place in the genus Polyporandra. 
In the Herbarium of the Royal Botanie Gardens at Kew I last 
year compared authentic specimens of the only hitherto described 
species of Polyporandra (P. scandens Buccart and P. Hansemanni 
Eneier) with JUNGHUHN’S unicum of the Leiden Herbarium. In so 
doing I have become convinced that Polyporandra scandens and 
Hansemanni are very closely related but that, as was indicated above, 
our species (Polyporandra JSunghuhnit) is sharply marked off from 
these specifically. 
In conclusion I wish to tender my best thanks to the Director of 
the Royal Botanic Gardens in Kew, for the facilities given me for 
the comparison of the above-mentioned authentic specimens of Breccari 
and of ENGLER. 
Leiden, February 26%, 1909. 
Physics. — “On the solid state”. By Mr. J. J. van Laar. (Communi- 
cated by Prof. H. A. LORENTz.) 
(Communicated in the meeting of February 27, 1909). 
1. In a recently published paper *) I treated the complete theory 
‘of association, not only for gases and vapours, but also for liquids. 
If we assume that only two simple molecules combine to a 
double molecule, the formula: 
5 PO ult ie hl ed, 
B RER me 4 BRE a ER | ee brats 
1—, pt ars 
holds universally, in which c is a constant to be determined, and 
further : 
kr Pee k, +- 2k, 
we Ab = —b, + 2b,. 
R . 
So the quantity yR is the change of the specific heat for infinitely 
great constant volume, when 1 Gr. mol. of double molecules passes into 2 
Gr. mol. of single molecules, while 45 is the change of the volume of the 
molecules in this transition. The quantity ¢, = — (¢,), + 2(e,), repre- 
1) In the Arch. Teyler (2) T. 11, Troisième partie, p. 235—331 (1909). 
52 
Proceedings Royal Acad. Amsterdam. Vol. XI. 
