272 Prof. J. Borgmann on the Influence of Light 



diameter 0'09 millim., quite unnecessary ; the displacement of 

 one centimetre of this wire representing but a small fraction, 

 0*06 of a milligramme. 



I state these particulars at length, as I do not at present 

 know of any other weighing machine in which a similar 

 degree of delicacy may be so combined with the qualities of 

 inexpensiveness and compactness, up to any ordinarily re- 

 quired power, as in this balance. 



XXVIII. On the Influence of Light upon Electric Discharge. 



By J. BORGMANN. 



To the Editors of the Philosophical Magazine and Journal. 

 Gentlemen, 



SOME highly interesting experiments of Hertz, Hallwachs, 

 Wiedemann-Ebert, and Arrhenius have proved irrefutably 

 the influence of ultra-violet light-vibrations on the electric dis- 

 charge of bodies in the air. Under the influence of light the 

 potential on bodies diminishes (especially if the potential be 

 negative); an electric current is even established between the 

 illuminated body and any other unisolated body. Some time 

 ago I published two articles *, in which I have tested the 

 transmission of the electric current through the air in its 

 ordinary state of elasticity and temperature. The flames or 

 points served me in my experiments as electrodes. The use 

 of such electrodes engenders a continual current through the 

 air, even at a comparatively considerable distance between 

 the electrodes. My experiments brought me to the conclu- 

 sion that in this case one must admit on the kathode-flame 

 considerably less particular resistance at the passage of elec- 

 tricity from the air to the electrode than on the anode-flame 

 at its passage from the electrode to the air. It seems to me 

 that there exists a link between recently made experiments, 

 demonstrating the influence of light on the diminution of the 

 potential upon bodies, and my own experiments. In both 

 cases we have the formation of the electric current in the 

 ordinary air — a fact usually not observed and even denied. 

 In the experiments of Hertz, Arrhenius, and others the electric 

 current in the air manifests itself in case of illuminating a 

 negatively charged body. According to my own experiments, 

 such a current is produced immediately between the flames 

 or points. But if in the first case the setherial vibrations of 



* Journal of the Russian Physico-Chemical Society, tt. xviii., xix. ; 

 La lumiere electrique, xxii. pp. 198, 276, xxvii. pp. 70, 126, 182 ; Phil. 

 Mag. xxiii. p. 384, xxiv. p. 374. 



