lo LarmoR, Physical Aspect of the Atomic Theory. 



re-aggregation of atoms to form new molecules, which 

 constitutes chemical reaction. Some day the ascertained 

 fact, that such influence of the close partial superposition 

 of the fields of energy of the adjacent atoms in the mole- 

 cule is at any rate almost infinitesimally small, may play a 

 part in the elucidation of the mode of operation of 

 gravitation. The essentially cognate fact, that no 

 intervening obstacle can modify sensibly the gravitation 

 of two masses, has already drawn us towards the position 

 that the nuclei of the fields of stress, which constitute 

 the physical aspect of atomic forces, are excessively small 

 compared with the distances apart of these interacting 

 nuclei in the fields of activity which are the atoms. 



In the same way the Daltonian principle, of a definite 

 molecule for each substance, now stands in intimate 

 connexion with the Berthollet idea of statistical or mobile 

 equilibrium, which requires that in the active interchange 

 that is always going on among ultimate constituents of a 

 substance, all the possible types of molecules which have 

 any degree of stability must be present in some amount,, 

 though in most cases practically infinitesimal. It has also 

 to take cognizance of fundamental considerations of a 

 biological character, which will be referred to later. 



While theory is aimless and impotent without 

 experimental check, experiment is dead without some 

 theory, passing beyond the limits of ascertained know- 

 ledge, to control it. Here as in all parts of natural 

 knowledge, the immediate presumption is strongly in 

 favour of the simplest hypothesis ; the main support, the 

 unfailing clue, of physical science is the principle that, 

 nature being a rational cosmos, phenomena are related 

 on the whole in the manner that reason would anticipate. 

 Radiation. 



In sketching the progress of the purely physical 



