1866.] 



Mr. Maxwell on the Dynamical Theory of Gases, 



167 



into the quieter pace of ordinary currents*. Many important conse- 

 quences in physiology and in pathology, as I think, result directly or 

 indirectly from this view of the matter, of which some are set forth in 

 some Lectures which I gave at the College of Physicians in London 

 three years ago, and which have since appeared in print ; but it is no 

 part of my present task to consider these consequences. Indeed, what I 

 proposed to do in this paper I have now done ; and this was simply to direct 

 attention to certain facts as facts, and to offer certain passing comments 

 suggested naturally by these facts. 



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

 well, F.R.S. L. & E. Received May 16, 1866. 



(Abstract.) 



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

 ing on one another with forces which are insensible, except at distances 

 which are small in comparison with the average distance of the molecules. 

 The path of each molecule is therefore sensibly rectilinear, except when 

 two 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 dis- 

 tance 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 mole- 

 cules 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 Prevost, 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 bodies, and I have given some applica- 



^ It is to be supposed that certain molecules in living animal bodies are, under cer- 

 tain given conditions, a constant source of electricity — are so, perhaps, in tlie way in 

 which certain molecules of the electrophorus are such a source. The idea is that this 

 electricity is so supplied as to admit of a series of frequent discharges, or to keep up a 

 constant current if these discharges are retarded sufficiently. At any rate, it does not 

 follow that this constancy of the current of animal electricity detected by the galvano- 

 meter is an objection in itself to the idea that the primary condition of animal electricity 

 may be, not current, but statical. 



