4*4 THB DYNAMICAL EVIDENCE OF TOE 



The relation between pressure and density arising from such an action 

 between the (articles is of this kind. 



As the density increases from zero, the pressure at first depends almost 

 entirely on the motion of the particles, and therefore varies almost exactly as 

 the prvwure, according to Boyle's Law. As the density continues to increase, 

 the effect of the mutual attraction of the particles becomes sensible, and this 

 causes the rise of pressure to be less than that given by Boyle's Law. If 

 the temperature is low, the effect of attraction may become so large in pro- 

 portion to the effect of motion that the pressure, instead of always rising as 

 the density increases, may reach a maximum, and then begin to diminish. 



At length, however, as the average distance of the particles is still further 

 liiminiahed, the effect of repulsion will prevail over that of attraction, and the 

 pressure will increase so as not only to be greater than that given by Boyle's 

 Law, but so that an exceedingly small increase of density will produce an 

 enormous increase of pressure. 



Hence the relation between pressure and volume may be represented by 

 the curve ABCDEFO, where the horizontal ordinate represents the volume, 

 and the vertical ordinate represents the pressure. 



the volume diminishes, the pressure increases up to the point C, then 

 diminishes to the point E, and finally increases without limit as the volume 

 diminishes. 



We have hitherto supposed the experiment to be conducted in such a 

 way that the density is the same in every part of the medium. This, how- 

 ever, is impossible in practice, as the only condition we can impose on the 

 medium from without is that the whole of the medium shall be contained 



