114 PROCEEDINGS OF THE AMERICAN ACADEMY 



7. If the particles were perfectly hard and spherical, the specific heat 

 under constant volume would be to that under constant pressure as 3 to 

 5. If they were hard, but not spherical, this ratio would be that of 

 3 to 4. The latter result follows from an elegant theorem given by 

 Professor Maxwell in Vol. XX. of the Philosophical Magazine ; viz. 

 that if the particles are hard, but not spherical, the sum of their vires 

 vivce of translation will be equal to that of their vires vivce of rotation. 

 Unless it can be shown that this ratio will be lessened by supposing 

 that the non-spherical particles are not hard and unyielding, which cer- 

 tainly seems improbable, this result will present the greatest difficulty 

 which the theory has to encounter. 



Considering the number and variety of the phenomena of gases 

 which are accounted for on this theory, and especially the exactness 

 with which it accounts for the hitherto inexplicable phenomena of dif- 

 fusion, there seems to be a considerable probability in its favoi*. The 

 small discrepancy between the observed and computed ratio of 

 the specific heats (1.42 and 1.33) may be found to proceed from 

 some property of the particles not taken account of in the mathemati- 

 cal analysis. 



The laws of diffusion are obtained on the hypothesis that the gases 

 are separated by an exceedingly thin partition, pierced with extremely 

 small holes. The change of temperature produced by motion proceeds 

 from the changed velocity of impact of the particles against the body, 

 each molecular impact producing a heat-wave. 



Professor Gray presented the following papers : — 



1. Characters of some Composites in the Collection of the 

 United States South Pacific Exploring Expedition under 

 Captain Wilkes, ivith Observations, <fec. By Asa Gray. 



Vernoniacece. 

 MoNOSis INSULARUM (sp. nov.) : fruticosa, laxe ramosa ; foliis ob- 

 longis acuminatis repando-dentatis basis cuneatis in petiolum attenuatis 

 puberulis supra glabratis subtus ad costam venasque cum ramis adpres- 

 so-tomentellis ; capitulis corymbosis ; pappi setis rigidis vix denticulatis, 

 majoribus apice clavellatis. — Tonga and Feejee Islands. A true con- 

 gener of M. Wightiana, DC, the type of the genus, which stands in 

 nearly the same relation to Gym.nanthem,um that De Candolle's section 

 Eremosis does to Vernonia. 



