38 PROFESSOR KELLAND, ON MOLECULAR EQUILIBRIUM, 



and B = Ae- at (l+al)-^-; 



1+al 3 1+al' 



The equations in (14) are not affected by this consideration, conse- 

 quently B is independent of the mean density ; and A is increased 

 proportionally to it. 



18. I propose next to determine the mutual action of two particles. 



We have seen that the atmosphere of any particle is perfectly in- 

 dependent of that of the surrounding particles : it follows, that the action 

 of two particles on each other, is also independent of the surrounding 

 medium. The latter supposes, however, that the pressure which is 

 exerted by the caloric is due to the actions of particles so arranged 

 as to produce equilibrium ; in fact, the pressure on the surface of a 

 material particle A, even as far only as it depends on the caloric which 

 constitutes the atmosphere of B, will vary with the attractions of the 

 other particles on it, except the system be in equilibrium, in which 

 case we may suppose, as we have already done, that the pressure cor- 

 responding to the density Doc D 



= hD. 



19. Our first point will be to find the value of this pressure. 



Let a be the distance between the centres of the particles, / their 

 radius, P any point in the particle on which the pressure is to be de- 

 termined; then the area of an annulus is QirPsmedQ, 



p—aR 



and the pressure on it ZwPhA —p- sinfleW; 



hence, the resolved part of the whole pressure in the direction of the 

 line joining the centres of the particles, is 



