Discharges in Insulators. 447 



experiments and 0. E. Meyer's Gastheorie, the factor being 



everywhere omitted. 10 



From these numbers we obtain a remarkable relation : it 

 follows, namely, from both the first and the second series, that 

 the product of the path-length and the minimum difference of 

 potential, measured at equal pressure, has nearly the same value 

 with all the gases investigated. 



Stefan pointed out the connexion between path-length and 

 index of refraction ; Boltzmann's experiments have shown 

 that the dielectric capacity of gases stands to the index of 

 refraction in the relation required by Maxwell's law ; and the 

 present investigation brings the insulating-power of gases into 

 causal connexion with the three above-mentioned properties. 

 Accordingly the insulating-power of a gas is by so much less as 

 the inductive capacity of the gas is greater, and vice versa. 



Similar simple relations exist between path-length and M. P. 

 for one and the same gas at different pressures ; a simple dis- 

 cussion of the experiments spoken of under question 1 leads to 

 this result. 



Besides the gases above adduced, olefiant gas was examined. 

 It was not found to conform to the same law ; for the products 

 of the M. P. and the path-length at the pressures 205 and 110 

 millims. were respectively 149 and 123. I believe, however, 

 that no importance need be attached to this deviation, since 

 the phenomena attending the discharges were of quite a differ- 

 ent character from those with the other gases, and permit us 

 almost certainly to conclude that decomposition of this gas 

 took place. 



In conclusion, in moist air the M. P., and consequently the 

 insulating-power, was much greater than in dry air. 



5. A series of experiments with air and hydrogen prove 

 that, cceteris paribus, the M. P. is less when the point is charged 

 with negative than when it is charged with positive electricity; 

 whether the like takes place also in regard to the difference of 

 potential at which the discharge commences I have not yet 

 been able to decide. 



Strasburg, May 1878. 



