; . TOT DYNAMICAL EVIDENCE OF THE 



the absolute temperature, and it is a constant for all gases. It follows from 

 this, that if several gases in the same vessel are subject to an external force 

 like that of gravity, the distribution of each gas is the same as if no other 

 gu were present This result agrees with the law assumed by Dalton, according 

 to which the atmosphere may be regarded as consisting of two independent 

 atmospheres, one of oxygen, and the other of nitrogen; the density of the 

 oxygen diminishing faster than that of the nitrogen, as we ascend. 



This would be the case if the atmosphere were never disturbed, but the 

 ^jfftnfc of winds is to mix up the atmosphere and to render its composition more 

 uniform than it would be if left at rest. 



Another consequence of Boltzmann's theorem is, that the temperature tends 

 to become equal throughout a vertical column of gas at rest. 



In the case of the atmosphere, the effect of wind is to cause the tem- 

 perature to vary as that of a mass of air would do if it were carried vertically 

 upwards, expanding and cooling as it ascends. 



But besides these results, which I had already obtained by a less elegant 

 method and published in 1866, Boltzmann's theorem seems to open up a path 

 into a region more purely chemical. For if the gas consists of a number of 

 similar systems, each of which may assume different states having different 

 amounts of energy, the theorem tells us that the number in each state is 



proportional to e" s where ^ is the energy, the absolute temperature, and K a 

 constant. 



It is easy to see that this result ought to be applied to the theory of 

 the states of combination which occur in a mixture of different substances. But 

 as it is .only during the present week that I have made any attempt to do 

 so, I shall not trouble you with my crude calculations. 



I have confined my remarks to a very small part of the field of molecular 

 investigation. I have said nothing about the molecular theory of the diffusion 

 of matter, motion, and energy, for though the results, especially in the diffusion 

 "f matter and the transpiration of fluids are of great interest to many chemists, 

 and though from them we deduce important molecular data, they belong to a 

 part of our study the data of which, depending on the conditions of the en- 

 counter of two molecules, are necessarily very hypothetical. I have thought it 

 better to exhibit the evidence that the parts of fluids are in motion, and to 

 describe the manner in which that motion is distributed among molecules of 

 different masses. 



