LIMITS OF INSULATION AND DISCHARGE IN GASES. 103 



gas in the vessel, yet we may for present purposes take the mean interval as repre- 

 senting in some degree that power. On examining these mean intervals as they are 

 given in the third column (1388.), it will be very evident, that gases, when employed 

 as dielectrics, have peculiar electrical relations to insulation, and therefore to induc- 

 tion, very distinct from such as might be supposed to depend upon their mere phy- 

 sical qualities of specific gravity or pressure. 



1395. First, it is clear that at the same pressure they are not alike, the difference 

 being as great as 37 and 110. When the small balls are charged positively, and with 

 the same surfaces and the same pressure, muriatic acid gas has three times the insu- 

 lating or restraining power (1362.) of hydrogen gas, and nearly twice that of oxygen, 

 nitrogen, or air. 



1396. Yet it is evident that the difference is not due to specific gravity, for though 

 hydrogen is the lowest, and therefore lower than oxygen, oxygen is much beneath 

 nitrogen, or than olefiant gas ; and carbonic acid gas, though considerably heavier 

 than olefiant gas or muriatic gas, is lower than either. Oxygen as a heavy, and 

 olefiant as a light gas, are in strong contrast with each other ; and if we may reason 

 of olefiant gas from Harris's results with air (1365.), then it might be rarefied to 

 two-thirds its usual density, or to a specific gravity of 9*3 (hydrogen being 1 ), and 

 having neither the same density nor pressure as oxygen, would have equal insulating 

 powers with it, or equal tendency to resist discharge. 



1397. Experiments have already been described (1291. 1292.) which show that the 

 gases are sensibly alike in their inductive capacity. This result is not in contradic- 

 tion with the existence of great differences in their restraining power. The same 

 point has been observed already in regard to dense and rare air (1375.). 



1398. Hence arises a new argument proving that it cannot be mere pressure of the 

 atmosphere which prevents or governs discharge (1377- 1378.), but a specific electric 

 quality or relation of the gaseous medium. Hence also additional argument for the 

 theory of molecular inductive action. 



1399. Other specific differences amongst the gases may be drawn from the pre- 

 ceding series of experiments, rough and hasty as they are. Thus the positive and 

 negative series of mean intervals do not give the same differences. It has been al- 

 ready noticed that the negative numbers are lower than the positive (1393.), but, 

 besides that, the order of the positive and negative results is not the same. Thus on 

 comparing the mean numbers (which represent for the present insulating tension,) 

 it appears that in air, hydrogen, carbonic acid, olefiant gas and muriatic acid, the 

 tension rose higher when the smaller ball was made positive than when rendered 

 negative, whilst in oxygen, nitrogen, and coal gas the reverse was the case. Now 

 though the numbers cannot be trusted as exact, and though air, oxygen, and nitrogen 

 should probably be on the same side, yet some of the results, as, for instance, those 

 with muriatic acid, fully show a peculiar relation and difference amongst gases in this 

 respect. This was further proved by making the interval in air 0*8 of an inch whilst 



