3 i8 HERMANN VON HELMHOLTZ 



series of electrical tensions due to friction, and the theory 

 of the electrical machine, satisfactorily from it. The most 

 important object of the work was, however, to set forth the 

 theory of those phenomena which appear when a fluid is flow- 

 ing past a solid wall, and to account for the transition between 

 the excitation of electricity by the galvanic opposition of 

 bodies at rest, and by the sliding friction of solid bodies. 

 Starting from the view that the fluid is in galvanic opposition 

 to the wall of the vessel, and that they both form an electrical 

 double layer along their surface of contact, he succeeded in 

 explaining two phenomena that are very closely connected 

 the propagation of fluids through narrow tubes, in consequence 

 of the passage of an electrical current through the same, and 

 the appearance of electromotive forces, when fluids are driven 

 through similar tubes by hydrostatic pressure. The theo- 

 retical developments and the comparison with the results of 

 G. Wiedemann and Quincke's experiments, however, refer 

 only to capillary tubes, while in wider tubes more complicated 

 phenomena of motion appear at the point at which the current 

 enters. In this paper, as in the Faraday Lecture later, and 

 in a series of subsequent electrical researches, Helmholtz 

 comes back repeatedly to the close connexion between the 

 electrical and the chemical forces, as well as to the explanation 

 of Volta's fundamental experiment. 



He assumes that electrical and chemical forces are essentially 

 the same, and supports the view that the presence of the forces, 

 which when unchecked set up chemical processes, suffices to 

 call out the corresponding electrical distributions, even before 

 the appearance of the chemical combination ; it does not seem 

 to him necessary that a complete chemical process must inva- 

 riably be the precursor of Volta's charges. Helmholtz is here 

 at one with Faraday, who assumed the identity of the forces 

 of chemical affinity with electricity, and expressed the view 

 that the atoms adhere to the electrical charges, and the opposed 

 charges again to each other, without thereby excluding molecular 

 forces, which act directly from atom to atom. 



Helmholtz regards Volta's much-contested experiments as 

 unimpeachable ; if a momentary metallic connexion be made 

 between a copper plate and a zinc plate, at minimal distance 

 from each other, and well insulated by bars of shellac standing 



