Attraction of Mass, and some New Gas Equations. 87 



We thus obtain a reduced "Border-curve" of the same 

 kind as the " Border-curve " of any particular gas, but 

 belonging to all substances that do not change their mole- 

 cules during isothermal compression. The curve 2p c . «?<?— 1 

 (vide fig. 1), consisting of vertices of various Border-curves, 

 *. e. of critical points, has disappeared. 



IV. 



The equality of action and reaction and the " Intrinsic 

 Pressure " it involves would explain the seemingly incon- 

 gruous course of a continuous isothermal below T c between the 

 two extreme values of p. For the pressure in the interior must 

 decrease as the intrinsic pressure increases, with the same 

 force pi. Once c has attained a value > the value ^v c or ^<j} Cy 



c 

 p x = — ■ is bound to increase more rapidly than IT owing to 



. v ° .1 1 



the influence of B, as soon as the density- exceeds -. This 



J V V c 



might also explain that this part of the curve cannot be realized 

 by the experiment. For condensation would set in first where 

 the pressure II obtains, i. e. between the surface and the 

 interior. 



The densities corresponding with II c = 3jo c in the layers 

 between surface and interior and p c in the interior should 

 cause different refraction, and a falling of the heavier layers 

 should be observed. 



The equality of p c and p 1(f can be proved also in the following 

 and completely independent manner and substantiated by 

 striking experimental evidence. As, according to van der 

 Waals' equation, pi =3/? c , it was the following deduction and 

 its experimental support which enforced the conviction that 

 at least the solution of that equation must be inexact. 



A second argument proving the Equality of p c and p 1(; . 



The "Inward Pressure " pi naturally opposes the thermic 

 pressure p towards the exterior causing expansion, and the 

 physical state of a substance must largely depend on the 

 relative values of these two forces. 



For a liquid (or solid) p 1 must be larger than p and the 

 substance must remain a liquid (or solid) as long as p\>p ; 

 the minimum value of p x cannot be less than p and must be 

 equal to p, in which case the substance is in an unstable 

 condition. 



For a gas (or vapour) p x must be smaller than p ; its 

 maximum value must be equal to p. For if p 1 becomes 



