114 THE NEW PHYSIOLOGY. 



volume. This could easily be allowed for by modifying 

 the equation. The essential cause is that the molecules 

 attract and combine with one another in various ways 

 which the equation does not express. The ideal gas 

 obeying the equation is a fiction. Thus the equation 

 fails to represent the reality which is there : it only 

 represents a tentative working hypothesis which is good 

 enough for certain immediate practical aims. 



We can easily see why the kinetic theory of gases 

 must break down. For there is nothing in the theory 

 to enable us to predict the endless phenomena which 

 appear when molecules come into close proximity with 

 one another under various conditions. Evidently the 

 molecules may, and do, enter into aggregations and 

 " chemical " combinations of all sorts, which can 

 only be discovered empirically. The latent energy 

 which manifests itself in these changes is part of this 

 empirical factor. The molecules may also dissociate 

 into atoms, and, as we now know since the discovery 

 of radio-activity, the atoms may themselves be dis- 

 sociating, with liberation of vast and hitherto unsus- 

 pected stores of energy. The reverse process, with a 

 corresponding locking up of energy, may also be occurring. 

 We are therefore now face to face with a question as to 

 what are the conditions of stability of an atom ; and 

 since, as the known facts indicate, atoms are not merely 

 compounds of other atoms similar in kind to those known 

 to us, the conceptions of mass and of energy are them- 

 selves under review, and can no longer be regarded as 

 fundamental. 



We have become accustomed to the idea that the 

 44 laws of Nature " represent truth of universal applica- 



