2 Prof. E. Edlund's Researches on the Passage 



this interpretation ; then, it is not at all the resistance of the 

 rarefied gas that forms an obstacle to the passage of the cur- 

 rent, but the obstacle must be sought at the point of passage 

 between the electrodes and the rarefied gas. The current, 

 therefore, if it could be introduced into the vacuum without 

 the aid of the electrodes, would be able to pass through the 

 vacuum without difficulty. The experiments which have up 

 to the present been made on the passage of electricity through 

 rarefied gases are, I am deeply convinced, in favour of the 

 correctness of this explanation. Besides, several physicists 

 have been led to declare that there really does exist, at the 

 point of passage between the electrodes and the rarefied gas, 

 a special obstacle to the propagation of the current. But, in 

 my opinion, they have not understood the true nature of that 

 obstacle, nor have they attempted to demonstrate that its 

 magnitude increases with the rarefaction of the gas; moreover 

 they have not attributed to it the high importance which 

 belongs to it. 



The result of the above-mentioned memoir, so far as it 

 regards the subject of the present, may be summed up as 

 follows : — If r is the obstacle to the propagation of electricity 

 which is situated at the point of passage between the elec- 

 trodes and the gas, i\ the electric resistance in a column of 

 gas of unit length, and I the distance between the electrodes, 

 r-\-i\l will be the sum of the resistance which the electricity 

 must overcome in order to pass from one electrode to the 

 other. Of these values, r increases continually in proportion 

 as the gas is rarefied, while i\ during the same time undergoes 

 incessant diminution. From a judicious interpretation of the 

 experiments which have been made, especially those of Hit- 

 torf, it follows that the augmentation of the first of these 

 quantities and the diminution of the other continued until the 

 gas had arrived at the greatest rarefaction it was possible to 

 obtain by means of the mercury pump employed. In the 

 space exhausted of air, r acquires such a value that it is im- 

 possible for the current to surmount it. If, then, the current 

 cannot traverse a vacuum, it is not because the value r x of the 

 resistance has become too great, but because r is augmented 

 to such a degree that the current is incapable of surmounting 

 it. Several properties of gases with respect to the passage of 

 electricity show that this interpretation of the resistance which 

 they oppose to its propagation is really the only true one. 



In my memoir before mentioned, I have formulated the 

 opinion that the principal obstacle encountered by the electric 

 current at the surface of passage between the electrodes and 

 the rarefied gas is due to an electromotive force producing a 



