134 JAMES CLEKK MAXWELL 



Puluj, and Obermeyer. Maxwell's coefticiottt 'OQ3(J5 

 is too largo, but -001 s2, tho eocllicient obtained by 

 supposing tho viscosity proportional to the square 

 root of the temperature, would be too small. 



It still remains true, therefore, that the laws of tho 

 viscosity of gases cannot be explained by the hypothesis 

 of tho impact of hard spheres ; but some deductions 

 drawn by Maxwell in his next paper from his sup- 

 posed law of proportionality to the first power of tho 

 absolute temperature require modification. 



It was clear from his experiments just described 

 that the simple hypothesis of the impact of clastic 

 bodies would not account for all the phenomena 

 observed. Accordingly, in IStlt), Maxwell took up 

 the problem in a more general form in his paper on 

 tho "Dynamical Theory of liases," Phil. Trans., 1SGG. 



In it he considered the molecules of the gas not 

 as elastic spheres of definite radius, but as small 

 bodies, or groups of smaller molecules, repelling ono 

 another with a force whose direction always passes 

 very nearly through the centre of gravity ot tho 

 molecules, and whoso magnitude is represented very 

 nearly by some function of the distance of tho centres 

 of gravity. "I have made," he continues, " this 

 modification of the theory in consequence of tho 

 results of my experiments on the viscosity of air at 

 different temperatures, and I have deduced from 

 these experiments that the repulsion is inversely as 

 the fifth power of tho distance." 



Since more recent observation has shown that tho 

 numerical results of Maxwell's work connecting 

 viscosity and temperature are erroneous, this last 



