On the Electrical Discharge through Rarefied Gases. 7 



concentrated into two currents of unequal intensity, which ex- 

 tend upon the epipolar curve in contrary directions from the 

 point of contact. This curve is, in the present case, the 

 great circle which lies in the equatorial plane, which is cut at 

 right angles by an infinite number of magnetic curves upon the 

 surface of the sphere. In addition to this double epipolar- 

 luminous stream, the free arc of light, corresponding to the two 

 touching electrodes, continues to exist undisturbed in the interior 

 of the sphere. It is only when both electrodes touch the sphere in 

 points of the epipolar-maguetic curve, that the two epipolar 

 double currents unite into a single double current, which pos- 

 sesses the luminous intensity of both the former arcs*. 

 Bonn, July 15th, 1858. 



II. Observations on the Electric Discharge. 



By M. PLUCKERf. 



On the Spectra in highly rarefied Gases of different kinds during 

 the passage of the electric discharge. 

 88. T BELIEVE that I was the first to declare positively that 

 A the luminous appearance which accompanies electrical 

 discharge through long tubes of rarefied gases, is (without con- 

 sidering the special phsenomena in the neighbourhood of the 

 two electrodes) entirely and completely attributable to the traces 

 of gas remaining in the tubes; further, that the beauty and 

 great diversity of such spectra for various gases offer a new cha- 

 racteristic for distinguishing them, and that any chemical altera- 

 tion in the nature of the gas maybe thereby at once recognized. 

 This seemed to me to be the most important part of the subject, 

 pointing, as it does, to a method of physico-chemical investiga- 

 tions of a new kind. 



89, I find that my opinion, that no particles of metal are 

 transferred from one electrode to the other, has been supported 

 by Mr. Gassiot J. Metal is transported from one electrode alone 

 — the negative one — to the portion of the inner surface of glass 

 immediately surrounding it; and such transportation occurs 



* The author states how the new point of vievT developed in the above, 

 threw such a clear light upon some further expenmeuts of his (see the 

 following paper), of which some use has been made in this communication, 

 that a revision of the latter was considered necessary before publication. 



t From Poggendorff's Annalen, vol. cv. No. 1, p. 7- 



X "The minute particles of platinum are deposited in a lateral direction 

 from the negative wire, and consequently in a different manner from what 

 is described as occurring in the voltaic arc (De la Rive, ' Electricity,' vol. ii. 

 p. 288), 80 that the luminous appearance of discharge I'rom the induction 

 machine can in no way arise from the emanation of parficlcs of the metal." 

 (Proceedings of the Royal Society, iVIarch 4, 1858.) 



