PROFESSOR IN BERLIN 295 



the chemical affinity be overcome by the electromotive force ; 

 the process may be persistently maintained by the diffusion 

 of the hydrogen, so that the initial presence of a limited quantity 

 of gas suffices for a long-sustained current. In order actually 

 to demonstrate the penetration of the gases into the platinum 

 in galvanic polarization, Helmholtz set up experiments in his 

 laboratory to see whether the hydrogen produced on one side 

 of a thin platinum plate by electrolysis could be detected after 

 a certain time at the opposite side, by the fact of its causing 

 galvanic polarization there. The paper laid before the Academy 

 on March 16, 1876, ' Report on the Experiments of Dr. E. Root 

 of Boston, on the Permeation of Platinum by Electrolytic Gases/ 

 established as a fact that hydrogen does make the opposite 

 side of the platinum more positive. 



The further question whether electric convection is electro- 

 dynamically equivalent to the passage of electricity in a con- 

 ductor, was answered in the ' Report on the Experiments on 

 the Electrodynamic Action of Electric Convection, as carried 

 out by Mr. Henry A. Rowland/ laid before the Academy on 

 the same day. The convection currents thus obtained could 

 actually be substituted for the motions of electricity in open 

 conductors, thus affording possibilities of deciding important 

 theoretical questions. The result of the experiments har- 

 monized both with the theory of W. Weber, and with Maxwell's 

 potential theory, which considered the dielectric polarization 

 of insulators. 



When an ebonite disk, gilded on both sides, was thrown into 

 rapid rotation round a vertical axis, between two resting disks 

 of gilded glass, while they were charged by means of a point 

 with positive or negative electricity from the coatings of a Leyden 

 jar, it was found that the action of this electricity conducted 

 by convection was not merely the same in quality as that of 

 the galvanic current, but that it agreed quantitatively also 

 with that required by Weber's theory. 



The proof hereby afforded that electricity transported con- 

 vectively with its carriers also has electromagnetic action, was 

 for Helmholtz (in conjunction with his previous work) conclusive 

 evidence that Neumann's extended law of potential must be 

 combined with Faraday's hypothesis, and that the appearance of 

 electric or magnetic lines of force in space is invariably asso- 



