-Resistance of Vacuum. 15 



then it is found that the tension necessary for the discharge 

 must increase with the distance between the electrodes, but 

 more slowly than proportionally to that distance. If the gas 

 is strongly rarefied, i\ can be neglected in comparison with r; 

 and the tension necessary for the discharge is then indepen- 

 dent of the distance between the electrodes. All these deduc- 

 tions are rigorously conformable to the observations cited. 



The fact that electricity cannot penetrate an almost com- 

 plete vacuum depends, then, according to this exposition, on 

 the resistance to its passage between the electrodes and the 

 surrounding medium having risen above a certain limit*, and 

 has by no means its reason for existence in the circumstance 

 that the resistance, properly so called, of the gas has received, 

 by the rarefaction, an insurmountable value; on the contrary, 

 the resistance of the gas is diminished when its rarefaction is 

 augmented, so that an absolute vacuum is to be regarded as a 

 good conductor. If that is the case, one ought to be able to call 

 forth, without employing electrodes, an electric motion in a 

 vacuum sufficiently complete for it to be impossible to pass a 

 current in it by means of electrodes. This is in reality what 

 Gassiot and Pliicker have already done, in their above-mention- 

 ed induction experiments with strips of tinfoil pasted to the 

 outer surface of the tubes. Morgan's experiment, however, 

 also mentioned above, might appear to be in contradiction 

 with the fact cited, since it was impossible to that physicist to 

 produce by influence a luminous phenomenon in the most per- 

 fect vacuum. But to this it may be objected that the absence 

 of a luminous phenomenon is not a positive proof that no elec- 

 tric motion took place in the vacuum. Morren, in his expe- 

 riments upon the passing of electricity through rarefied gases, 

 saw that a galvanometer inserted in the circuit gave an evi- 

 dent deflection before it was possible to perceive any electric 

 light in the tube, although the experiment took place in a 

 dark roomj. The reason that in Morgan's experiment no 

 electricity passed to the mercury column was simply that there 

 was a resistance to its passage between the mercury and the 

 vacuum. 



I have not been able to find a single certain experimental 

 proof that absolute vacuum is a nonconductor: on the con- 

 trary, every thing indicates that vacuum is a good conductor 



* I have designated as a resistance the obstacle which the cm-rent has 

 to surmount in order to pass from the electrodes to the gas, or vice versa ; 

 now by that I do not at all mean that the obstacle is due to a resistance 

 in the ordinary meaning of the term, but rather that it is an electromotive 

 force producing in this respect the same effect as an ordinary resistance. 



t Ann. de Chim. et de Phys. (-4) iv. p. 337. 



