390 Royal Society : — 



not only does the proportion of lime in the precipitate decrease 

 while that of the magnesia increases, but the sum of the bases 

 falls from 3 to a little less than 2 equivalents. With ten mole- 

 cules, Mg CI 2 , in the solution, the precipitate is almost pure 

 ammoniacal phosphate of magnesia with very little lime. 



By comparing the experiments mentioned with those of Debus, 

 the author finds that the latter will give. results quite similar to 

 his own, and that some of the conclusions which he deduces are 

 to be regarded as not proved. 



LIII. Proceedings of Learned Societies. 



ROYAL SOCIETY. 

 [Continued from p. 313.] 



May 31, 1866.— Dr. W. A. Miller, Treas. & V.P., in the Chair. 

 rf^HE following communication was read : — 

 JL "On the Dynamical Theory of Gases." By J. Clerk Max- 

 well, F.R.S.L. & E. 



Gases in this theory are supposed to consist of molecules in motion, 

 acting on one another with forces which are insensible, except at 

 distances which are small in comparison w T ith the average distance of 

 the molecules. The path of each molecule is therefore sensibly 

 rectilinear, except when tw T o molecules come within a certain distance 

 of each other, in which case the direction of motion is rapidly 

 changed, and the path becomes again sensibly rectilinear as soon 

 as the molecules have separated beyond the distance of mutual 

 action. 



Each molecule is supposed to be a small body consisting in general 

 of parts capable of being set into various kinds of motion relative 

 to each other, such as rotation, oscillation, or vibration, the amount 

 of energy existing in this form bearing a certain relation to that 

 which exists in the form of the agitation of the molecules among 

 each other. 



The mass of a molecule is different in different gases, but in the 

 same gas all the molecules are equal. 



The pressure of the gas is on this theory due to the impact of the 

 molecules on the sides of the vessel, and the temperature of the gas 

 depends on the velocity of the molecules. 



The theory as thus stated is that which has been conceived, with 

 various degrees of clearness, by D. Bernoulli, Le Sage and Pre- 

 vost, Herapath, Joule, and Kronig, and which owes its principal 

 developments to Professor Clausius. The action of the molecules on 

 each other has been generally assimilated to that of hard elastic bo- 

 dies ; and 1 have given some application of this form of the theory to 

 the phenomena of viscosity, diffusion, and conduction of heat in the 

 Philosophical Magazine for 1860. M. Clausius has since pointed 

 out several errors in the part relating to conduction of heat ; and the 

 part relating to diffusion also contains errors. The dynamical theory 



