178 Dr. E. Goldstein on the Electric 



discharge conveyed by the gas contained in them passes 

 through the fine pores in the paper cylinder, which behaves 

 qualitatively like a metallic electrode of similar shape. I 

 have carried ont the comparison of these imitation electrodes, 

 consisting of a network of pores in an insulating material, in 

 respect of thirteen properties independent of each other, and 

 in all respects have found the coincidence complete. The 

 magnetic surface of Pliicker, the production of phosphores- 

 cence by the ends of the rays, the envelopment by a dark 

 space on the side of the positive light, and so on, are all found 

 with these imitation kathodes. Instead of paper, spun glass 

 may be employed, and, generally, instead of an insulating sub- 

 stance an insulated metallic network. 



These results are obtained in consequence of the pheno- 

 menon already mentioned, that the last section of a narrow 

 tube introduced into the path of the discharge behaves as a 

 new negative pole on the side of the anode. The light emitted 

 by the secondary negative pole agrees also quantitatively 

 more nearly with that from a metallic kathode, the more the 

 section of the narrow tube differs from that of the wider tube 

 joined to it. On the other hand, the light emitted by the 

 secondary pole passes into positive light as soon as the section 

 of the narrow tube is not much less than that of the part join- 

 ing onto it. 



One result obtained with the imitation kathodes is important 

 — namely, that when the sum of the small openings of such a 

 kathode is equal in section to the section of the wider tube 

 surrounding it or joining onto it, all the openings, as far as can be 

 observed, produce the same action (brightness excepted) as if 

 each were present alone. The effects of the discharge are then 

 dependent upon the magnitude of the separate openings, and not 

 upjon the total section of the discharge. 



When the pores of the imitation kathodes, of other materials 

 than paper, were made smaller than was possible with paper, 

 the phenomena agreed so remarkably with those obtained with 

 actual metallic electrodes, even to the exact colour of the dis- 

 charge, that more than once it was necessary to take the tubes 

 apart and put them together again with greater care, to be con- 

 vinced that the phenomena were really due to the action of 

 pores and not of metallic poles. 



On the Mode of Discharge in Rarefied Gases. 



If we have (1) a discharge-tube in which the terminal wire 

 b represents the anode, and the flat electrode a (which occupies 

 the section of the tube at the other end) represents the kathode, 

 * Berl Akad. JBer. 1876, p. 280. 



