PROFESSOR IN BERLIN 331 



The subject was incomprehensible to me, as he discoursed for 

 the most part on atoms, and the influence of electricity on 

 chemical properties : but the enthusiasm when he entered, and 

 the cheers whenever he expressed his own conclusions or 

 opinions, were delightful.' 



Commencing with an historical review of the development of 

 Electrodynamics, which culminated in a brilliant exposition of 

 the Faraday- Maxwell Theory, he for the first time gave a 

 connected account of the relation between electrical and 

 chemical forces, as we have followed it above in his separate 

 publications. To arrive at an understanding of the relations 

 between electrical forces and chemical affinity, he shows from 

 the phenomena of electrolytic dissociation how we are to picture 

 the ponderable atoms as bound up with electricity. He con- 

 cludes from the assumption that ions are charged with electri- 

 city, that a wandering group of atoms invariably carries the same 

 charge of electricity with it, and that electricity itself is com- 

 posed of definite elementary particles which behave like the 

 atoms of electricity. An essential factor in chemical affinity is 

 formed by the attractions of the opposite electricities for each 

 other in the compounds. When a unit of positive electricity in 

 an atom is held by the unit of negative electricity in another 

 atom, these electricities will be externally inactive, and the atoms 

 will adhere together with saturated affinity. 



In Hertz's opinion this theory gives us a consistent representa- 

 tion of the nature of valency, and this alone he considers a 

 sufficient proof of the weight and significance of the conceptions 

 evolved by Helmholtz of chemical processes. When, on his 

 seventieth birthday, Hofmann spoke of his researches in the 

 interpretation of chemical processes as the inauguration of a 

 new era in chemistry, by means of which new light had been 

 cast upon entire regions, and these had been brought essentially 

 nearer to our comprehension, Helmholtz expressed his thanks 

 in the most modest words : 



' I am exceedingly grateful that you recognize and feel an 

 interest in my amateur efforts in chemistry, and are so good as 

 to tell me so.' 



After delivering the Faraday Lecture in London, Helmholtz 

 went on to Cambridge, where he was made Doctor of Laws ; 

 stayed some time in Glasgow with his friend W. Thomson ; 



