Electric Discharge in Gases. 



47 



of two wires of iron and German-silver soldered together, 

 was kept in contact with the outside of the tube by means of 

 a spring, and the deflections read off upon an astatic galvano- 

 meter. These give a measure for the heating of the glass 

 tube ; and this is nearly proportional to the heating of the 

 portions of gas close at hand. The experiments were always 

 so arranged that the thermo-electric element was moved from 

 the electrode towards the positive light, and back again in the 

 opposite direction ; the deflections were only noted after they 

 had become constant. 



In the following tables we give the differences of the de- 

 flections A observed at the position of the positive light, and at 

 different distances E from the kathode. The length of the dark 

 kathode-space was taken as measuring the pressure. In the 

 curves the abscissae represent the distances from the kathode, 

 and the ordinates the deflections of the galvanometer. 



I. A first series of experiments was made with a thin- walled 

 glass tube 25 inillim. wide ; the electrodes were circular 

 plates (fig. 5). 



Exhaustion high. Dark space 37 millim. Green light 

 faintly visible. Limit of positive light 210 (curve a). 



E. 





 13 

 32 

 42 



27 

 20 

 17 



17 



E. 



Dark space 30 millim 

 light at 220 (curve b). 



90 

 122 

 160 



22 

 23 

 22 

 18 



E. 



A. 



210 



9 



250 



3 



290 







No green light. Limit of positive 



E. 



A. 



E. 



A. 



E. 



A. 







19 



70 



23 



190 



9 



11 



17 



108 



20 



220 



3 



32 



17 



160 



13 



280 







Dark space 20 millim. No green light. Limit of positive 



rht at 200 



(curve c) 











E. 



A. 



E. 



A. 



E. 



A. 







23 



70 



18 



140 



5 



20 



17 



95 



13 



200 



4 



32 



19 



105 



10 



280 







48 



17 











