Dr. S. Guggenheimer on the Spark-discharge. 315 



at atmospheric pressure to be 31,000 volts. This gives 



X X 



— =40*8. The fact that the values of — are nearly coinci- 

 p p J 



dent seems to entitle one to draw the above conclusion. I 



hoped to be able to calculate the values of — for a wider 



P 

 range of pressures from the recent observations of Orgler*, 



but I was prevented from so doing as his numbers and curves 

 do not apply for greater distances of the electrodes than 0*5 

 and 0*6 cm. respectively. Paschenf, also, in his well-known 

 paper, does not give enough observations for a spark-length 

 of 1 cm. at different pressures to enable me to calculate the 



X 



values of — in a sufficient number of cases. 



P 



Starting from the fact already mentioned, that even air at 



atmospheric pressure always contains ions, and that ions are 

 continuously produced, it seems possible to obtain a fairly 

 clear idea of what happens before a spark passes, as well as 

 what happens during the spark-discharge. 



If, for instance, one subjects two electrodes to slowly in- 

 creasing electromotive forces, there will be formed immediately 

 a very feeble current, as observed by Warburg and other 

 experimenters. This current will, so long as no external 

 agents are acting, remain constant within very wide ranges 

 of the E.M.F.; but its intensity will increase very quickly 

 and tend to a maximum, as soon as the E.M.F. attains the 

 value necessary to give to the ions the velocity required to 

 produce new ions by impact. 



It seems to me that the experiments of Kreusler J prove 

 this very decidedly. It ought to be observed that in all his 

 experiments (the final ones) the electrodes were exposed to 

 ultra-violet light, but nevertheless when he approached the 

 discharge-potential, a change in the value of the E.M.F. of 

 1*7, 1*7, and 1*3 per cent, (he used Pt, Ou, and Fe elec- 

 trodes) corresponded to an increase in the intensity of the 

 current of 337*2, 243*1, and 392 per cent. The theory 

 strongly demands that just as the spark-potentials are approxi- 

 mately the same, so also these last numbers ought to be the 

 same ; but it seems that here secondary circumstances of the 

 experiments exert a certain influence. 



Let us assume, for instance, the intensity of such a satu- 

 ration current between the two electrodes to be only y-J-^ 



* A. Or<?ler, Ann. d. Phusik, i. p. 159 (1900). 

 t F. Paschen, Wied. Attn, xxxvii. p. 69 (1889). 



% H. Kreusler, Ver. Thys. Ges. Berlin, 1898. p. 80. especially table, 

 p. 91. 



