CONDUCTIVITY OF GASES AND VAPOURS. 411 



increases with very great rapidity, and all experiments tend to show 

 that electricity cannot pass in a perfect vacuum. 



Edlund* considers the resistance which gases present to the 

 passage of electricity as due to two causes the one a true 

 resistance, which decreases indefinitely with the pressure ; and to 

 an inverse electromotive force developed by the contact of the 

 gas and of the electrodes, which on the contrary increases with 

 the rarefaction. 



Another circumstance which complicates the phenomena, and 

 to which it is difficult to assign its part, is the transport of 

 electricity by the molecules of the gases themselves. And, not- 

 withstanding numerous researches on this question, it seems 

 difficult to form an exact idea on the true conductivity of 

 gases. 



* Ann. de Chim. et de Phys. [5], Vol. xxvn., p. 114. 1882. 



