INAUGURAL ADDRESS. 9" 



of the kind called positive ; and this mav involve the conception 

 that an originally wholly material molecule interacts in solution 

 with an originally wholly electrical molecule (a neutral combination 

 of the positive and negative electrical atoms) to form two dissimilar 

 ions, each containing a fraction of the material molecule combined 

 with a fraction of the electrical molecule. Such an action is 

 essentially reversible, two ions of the opposite kind being liable, 

 when they collide, to reform the original molecules — the wholly 

 material and the neutral electrical ; and quite similarly, new 

 combinations may result from the collisions of ions originally- 

 formed from different substances. Thus, less than a quarter of 

 a century ago the mental vision of the chemist became enriched. 

 Molecules he had known, and he was more or less familiar with 

 their atomic structure. The birth of new molecules by atomic 

 re-arrangement at the moment of molecular impact w^as a favourite 

 conception of his. Now ions, or molecules containing both material 

 and electrical atoms, were discovered to his vision, and he became 

 absorbed in studying them and the results of their encounters. 



No such new idea is ever accepted at once and by all. There 

 are always difficulties, or apparent difficulties, in the wa\'. Some 

 are struck chiefly by the difficulties and figure at first, at least, as 

 opponents of the theory ; others are struck mainly by its beauty 

 and manifest advantages and incline to accept it ; all, if they 

 be properly constituted, agree to abide by the results of further 

 investigation. And the results of such research are, as a rule, to 

 show that the theory, if correct in its essentials, requires more or 

 less modification in its details, but is capable of large extension. 

 So it has proved with the ionic theory. The result of a huge mass 

 of later quantitative investigation has been, I think, to prove the 

 following facts : — Ions are formed spontaneously by the solution 

 of certain kinds of molecules in certain kinds of solvents, as, for 

 instance, by that of salts in water. This " ionisation " does result 

 in the divorce of one part of the material molecule from the other, 

 as, for instance, of the sodium from the chlorine of common salt, 

 and in the charging of the one positively and of the other negatively. 

 The ions so formed do migrate independently in the solution, and 

 may become independent agents of chemical change ; and they 

 do serve as the actual carriers of the current. But they do not, as 

 a rule, follow the expected simple mathematical law as to the 

 frequency of their encounters — the law which it was thought should 

 regulate the numerical relation at any moment between the free 

 ions and the unionised molecules ; and here we have the chief 



