494 Lord Rayleigh on the Pressure of 



problem in itself has no physical meaning. For, according 

 to the doctrine of the immobility of the aather, it is an 

 absurdity to speak of forces acting upon or stresses existing 

 in the aether. 



Let us now consider this theory in its application to the 

 electroidic phenomena of hydrodynamics. Just as well as 

 an observer of these phenomena might arrive at Maxwell's 

 views, he might, with his limited knowledge of the things 

 before him, arrive at the views of Lorentz. But, as we see 

 at once, they do not hold. For the hydrodynamic actions at 

 a distance do depend upon a stress, although a much simpler 

 one than that found by Maxwell. 



The question to what extent it may be allowable to draw. 

 from the electroidic phenomena of hydrodynamics, positive 

 conclusions as to real electric phenomena may be open to 

 discussion. The intimate nature of the analogy makes it 

 very probable that useful suggestions may be obtained from 

 this analogy. But of course the method must be tried 

 with the greatest caution. The results produced here may 

 perhaps encourage electricians to take up the stress-problem 

 upon a wider base than Maxwell himself was able to do at his 

 first attack upon this, the fundamental problem of the theory 

 of electricity. The solution may be simpler than we expect. 

 For the hydrodynamic results plainly show that even the 

 simple isotropic stress may produce actions of the kind, 

 which Maxwell supposed explicable only as the effect of a 

 stress of the anisotropic type. 



XLV. On the Pressure of Gases and the Equation of Virial. 

 By Lord Rayleigh, (KM., F.R.S.* 



IF on be the mass of a particle, "V its velocity, p the pres- 

 . sure and v the volume of the body composed of tbe- 

 particles, the virial equation is 



i$mY 2 = %pv + i$p<f>(p), .... (1) 



where further p denotes the distance between two particles 

 at the moment under consideration and <f>(p) the mutual 

 force, assumed to depend upon p only. If the mutual forces 

 can be neglected, either because they are non-existent or for 

 some other reason, (1) coincides with Boyle's law, since the 

 kinetic energy is supposed to represent temperature (T) . 



According to some experimenters, among whom may be 

 especially mentioned Ramsay and Young, the relation between 



* Communicated by the Author. 



