370 Prof. E. Wiedemann on the Behaviour of Gases 



In a third series the electrodes were spheres, the gas was 

 hydrogenj the water-equivalent was 7*4. Tho following 

 numbers were obtained : — 



p 



a. 



b. ■ 



+ 



- 



+ 



- 



31 

 2-7 

 02 



X 



0-94 



0-227 



Oil 



0-21 



0-93 

 0-42 

 1-31 

 1-66 



096 



0-20 



0-064 



036 



0-83 

 0-40 

 1-33 

 2-40 



The conclusions to be drawn from the tables are as fol- 

 lows : — 



(1) The heating at the jiositive electrode diminishes continu- 

 ally and rapidly as the pressure decreases. At very low pres- 

 sures there is occasionally a small increase. At the same time 

 the glass round it shines with green light, as if the electrode 

 became temporarily negative. 



(2) The heating at the negative electrode at first decreases as 

 the pressure becomes less, and then increases rapidly. 



The heating results partly from the heating of the electrode 

 itself, partly from that of the enclosed gas, and partly from 

 that of the glass envelope. At quite low pressures, at the 

 negative pole, where the glass becomes luminous, no doubt the 

 last of these is the most important. I have calculated how 

 great the heating of each square cubic centimetre of the wall 

 would be under the conditions of the experiments, on the 

 assumption that the whole of the heat at the end of the 

 discharge issuing from the negative electrode is produced 

 upon the glass wall. I chose for this purpose the obser- 

 vations with point electrodes given under a, at very low 

 pressures. The luminous surface of the glass had a mag- 

 nitude of 5 square centimetres ; upon this surface there was 

 produced in each minute a quantity of heat of 0*77 x 6*4 

 = 4*9 calories, or 0'98 per square centimetre. By way of 

 comparison, it may be mentioned that the radiation of the sun 

 causes each minute a production of heat on each square centi- 

 metre of the earth's surface amounting to about 2 calories. It 

 is to be observed, however, that the discharge from the nega- 

 tive pole lasts only a very short time (not even the thousandth 

 part of the whole time), whilst the radiation of the sun acts 

 continuously for the whole time. 



A large number of measurements with electrodes of dif- 

 ferent forms were made, to determine the influence upon the 

 heating at the electrode of introducing air-sparks of varying 



