Discharge in Rarefied Gases. 369 



from the experiments which prove this, that that medium 

 must be essentially concerned in the discharge which, accord- 

 ing to our present views, together with the gas-molecules, the 

 particles of the electrodes of the walls, and any other solid 

 substances which may be present, occupies the space in which 

 the discharge takes place — that is to say, the aether. 



According to my view, the discharge is a process which 

 takes place in the free aether. I have already indicated this 

 view in the work already several times mentioned, and will 

 now give other evidence supporting the observation made 

 there. 



Hittorf* found that the resistance of the positive light 

 always decreased as the exhaustion of the gas increased ; on 

 the other hand, he thinks he has shown that the resistance 

 increases with the exhaustion in the kathode-light and at the 

 surface of the kathode. Changes in the form and magnitude 

 of the anode have no influence on the resistance. The great 

 resistance which offers itself to the discharge at an extreme 

 exhaustion, and finally leads to its extinction in a vacuum as 

 perfect as possible, depends therefore altogether upon the 

 resistance at the surface of the kathode and in the space filled 

 by the kathode-light. After I had recognized that the pecu- 

 liarities of the negative light might be produced at any point 

 whatever of the column of positive light by simple changes in 

 the cross section of the discharge-tube, and that each separate 

 stratification of positive light is nothing else than a modified 

 bundle of negative light, this opposition between kathode- 

 light and positive light appeared to me just as doubtful as 

 already a number of other supposed differences between the 

 two, which I had found not to exist. 



I found in fact that, exactly as with the positive light, the 

 resistance of the kathode-light at small pressures becomes vanish- 

 ingly small in comparison with the total resistance of the dis- 

 charge. Hence, since ho specific resistance exists at the anode, 

 and since further, as already mentioned, the resistance of the 

 positive light vanishes in comparison with the total resistance 

 of the discharge, it follows that the resistance to the discharge 

 at very small pressures takes place entirely at the surface of the 

 kathode. 



My experiments on this subject were not made by means of 

 a galvanometer, like those of Hittorf, but by means of the 

 spark-micrometer, which is here much more efficient. The 

 spark-micrometer was included in a second circuit connecting 

 the electrodes, and the distances of the poles of the micrometer 

 compared for the different densities of gas and lengths of 

 * Hittorf, Pogg. Ann. cxxxvi. p. 1 (1869). 



