PROFESSOR IN BERLIN 375 



and that with vertical incidence the reflected waves interfere 

 with the incident, and give rise to stationary waves in the air, 

 he concludes his letter with the words, ' Hertz's work is the 

 work of a genius/ 



Helmholtz's desire to conclude a series of hitherto un- 

 finished investigations had led him back in the summer of 1887 

 to the subject of electrolysis. On July 28 he made a com- 

 munication to the Academy ' On Further Investigations on the 

 Electrolysis of Water', which he linked on to his first paper 

 * On the Thermodynamics of Chemical Processes ', written in 

 1883, giving experimental proof of a number of the results 

 therein deduced theoretically. He had previously discovered 

 in theory that the electrolytic dissociation of water must occur 

 with less electromotive force according as the quantities of 

 oxygen and hydrogen dissolved in the proximity of the elec- 

 trodes are smaller, and that no inferior limit other than zero 

 could be given to the smallest electromotive force capable of 

 dissociating perfectly gas-free water. The experimental deter- 

 mination of this law, however, had presented great difficulties, 

 inasmuch as the platinum anode, or both electrodes, contain 

 occluded hydrogen or combustible gases, with which the 

 oxygen conveyed by the current combines, so that a much 

 lower E.M.F. can liberate bubbles of hydrogen at the cathode. 

 The construction of a special apparatus and most accurate 

 measurements now yielded a satisfactory reconciliation of theory 

 and experiment. 



Helmholtz was also contemplating the extension and definite 

 conclusion of his thermodynamic and chemical researches in 

 a paper of the widest scope which was to be entitled ' Thermo- 

 dynamic Considerations as to Chemical Processes'; but of 

 this only a few fragments remain, in particular the Introduction, 

 designed for a large circle of readers, which summarizes the 

 researches of Berthelot and other workers, and is of great 

 interest on account of its clear historical exposition of the 

 theories of physical chemistry that had come so prominently 

 forward in the last ten years. 



The parting of Helmholtz from the great society of Members 

 and Associates of the Berlin University, to which, properly 

 speaking, he belonged only as an honorary member from this 

 time forward, is marked in the history of his untiring scientific 



