58 MOLECULAR AND ATOMIC ENERGY 135 



is much greater, and the variation seems the greater the 

 more atoms there are in the molecule. 



This remark leads to a simple explanation on the basis 

 of the previous discussions upon the nature of the mole- 

 cular and atomic energy. A possible cause was there 

 indicated in the circumstance that the atomic energy is not, 

 like the molecular energy, simply kinetic, but partly consists 

 of the potential energy of chemical affinity, and that the 

 latter is perhaps subject to different laws. If this is true, 

 the variation must prove the greatest where the greatest 

 forces of affinity come into play, and, therefore, will be the 

 larger the more atoms are chemically combined. And this 

 is in fact the case. 



It still remains for us to explain why the ratio of the 

 atomic energy c to the molecular energy E increases, and 

 does not diminish, as the temperature rises. This fact is 

 indeed to be explained only thus, that the so-called disgre- 

 gation or loosening of the chemical bonds of the atoms 

 combined in the molecule requires an expenditure of energy 

 which is the greater the further it has already proceeded in 

 consequence of increase of the temperature. 



This assumption contains nothing improbable, provided 

 that we suppose that the force of chemical affinity does not 

 bring the atoms into direct contact, but endeavours to hold 

 them at a certain distance from each other ; they can then 

 oscillate about their assigned positions of equilibrium, and 

 rotate or move about in any other way. By addition of 

 heat these motions will be accelerated, and the amplitude 

 of the oscillations and, above all, the lengths of the 

 paths will be increased without at first causing the atom 

 to escape out of the range of action of the forces of affinity. 

 For this proportionally little energy is needed. Far more 

 energy, however, is required when the atom begins by its 

 increased speed to break loose from the bonds of the mole- 

 cule, because now the opposing chemical forces are to be 

 overcome. 



This explanation of the behaviour observed byWiillner 

 seems to contradict the fact that, according to the obser- 

 vations of P. A. Mil Her, some substances act exactly 



