260 Propagation of Electricity in highly Rarefied Elastic Fluids. 



the two thermometers finally approximate to each other, and even 

 after a certain time become the same. 



Hydrogen and nitrogen give the same results. 



The numbers representing the temperatures in the foregoing 

 Tables cannot be given as perfectly exact ; they vary, in fact, as 

 to their absolute values, with the intensity of the electric jet ; 

 but they are sufficiently constant and exact to prove : — 



1. That the transmission of the electric discharge through 

 rarefied gases is accompanied by a sensible elevation of tem- 

 perature ; 



2. That, when the gases are sufficiently rarefied for the dis- 

 charge to pass readily, and for the light to be stratified, this ele- 

 vation of temperature is less near the negative electrode than it 

 is near the positive electrode; 



3. That the absolute rise of temperature at the two electrodes, 

 and the differences between them, vary with the density and 

 nature of the gas *. 



A fact which strikingly proves the great calorific and illumi- 

 nating power of electricity is that hydrogen, under a pressure of 

 only 1^ millim., may be rendered luminous and become sensibly f 

 heated by the passage of electricity, although at this pressure its 

 density is so small that a cubic centim. of the gas weighs scarcely 

 more than 5 oW °f a milligramme. 



When one sees that so subtile a substance as hydrogen reduced 

 to 1 or 2 millims. pressure is capable of becoming luminous 

 under the influence of electricity, it is impossible not to be 



* The experiments recorded above must not be confounded with those 

 that have been made as to the temperature of the electrodes between which 

 the electric discharges are passed through the elastie fluids. Mr. Gassiot, 

 who has given much attention to this latter class of phenomena, has shown 

 that it depends on the dimensions of the electrodes, and upon the nature 

 or greater or less degree of continuity of the electric discharges, which cir- 

 cumstances sometimes cause the positive electrode and sometimes the ne- 

 gative to be most heated. He concludes from his numerous researches 

 that the development of heat, whether at the positive or the negative elec- 

 trode, results exclusively from the resistance which is opposed to the trans- 

 mission of the electricity at these two parts of the circuit respectively. My 

 experiments were made with two electrodes whose size was too great for 

 them to become heated (copper knobs, from half a centim. to one centim. 

 in diameter) ; the results obtained can therefore be due only to the more 

 or less elevated temperature of the different portions of the rarefied gaseous 

 column traversed by the electric jet which escapes between the two elec- 

 trodes. 



f The gas must in fact have been very considerably heated for it to have 

 been able to raise the temperature of a thermometer of which the bulb, 

 filled with mercury, was a cylinder *2\ millims. in diameter and 3 centims. 

 long 3° in two minutes. The simple fact that the gas becomes luminous 

 is a further proof of its high temperature; for its luminosity is evidently 

 pnlv a result of its incandescence. 



