32 G M. P. Riess on the Passage of Electric Currents 



current. When the current of a powerful voltaic battery is 

 allowed to pass in a luminous manner between two wires in fi'ee 

 air, the wire which forms the positive electrode is more heated 

 than the other, and is the first to become incandescent and to 

 fuse. When, on the contrary, the current of an induction ap- 

 paratus is allowed to pass with sparks between two equal wire 

 points in air, that wire only becomes incandescent and fuses 

 which forms the negative electrode of the interruption current, 

 and which, as I have long ago shown, can be easily recognized 

 by the covering of blue glimmering light upon it. Hitherto 

 this paradox has not been solved. Is it not possible that the 

 interruption current, part of which apparently passes here as a 

 glimmering discharge, has but little heating eflPect, but on the 

 other hand increases the conductibility of the space, and facili- 

 tates the passage of the contact current, which manifests itself 

 principally by the incandescence of the wire end ? It would then 

 be the positive electrode of the latter current which produced the 

 greatest heat, so that between the action of a voltaic and that of 

 an induction current no difference would exist. This would be 

 a very simple and acceptable solution of the paradox. 



The above research by Prof. Riess was communicated to the 

 Academy of Berlin on the 18th of June, and shortly afterwards, 

 on the 30th of July, M. Gaugain made another communication 

 to the Academy of Paris "On the Electric Conductibility of Air*.'' 

 Having shown in a preceding communication f, that, within 

 certain limits, the conductibility of air appeared to decrease with 

 its density, he deemed the fact of sufficient theoretical import- 

 ance to demand re-examination, with a view of more completely 

 substantiating the fact. In his last I'csearch, the apparatus de- 

 scribed under the name of an electric valve was sometimes em- 

 ployed, and sometimes simple tubes with metallic wires for elec- 

 trodes. The general result obtained with all the apparatus was 

 the same. When the induced currents of Ruhmkorft's apparatus 

 were passed through air whose density was gradually diminished, 

 the intensity of the electricity, as shown by a galvanometer, 

 began at first to increase (departing from the atmospheric 

 pi-essure), attained a maximimi, afterwards began to decrease, 

 and finally attained a minimum value when the vacuum was as 

 perfect as possible. The density of air corresponding to the 

 maximum intensity of current varied with the magnitude and 

 disposition of the apparatus, \\'\i\i the distance between the elec- 

 trodes, and with the superficial magnitude of the latter. At one 



* Compfes Rendus, vol. xli. p. 152. 



t Ibid. vol. xl. p. 640, and Phil. Mag. vol. x. p. 207. 



