Electric Intensity and Conductivity in Rarefied Gases. 515 



one direction and then in the other, and the mean of the two 

 results, which never differed much, was taken. The Clark 

 cell and galvanometer were well insulated, so that the 

 small electrodes could take up the potential of the discharge. 

 The platinum plates disturbed the luminous parts of the 

 discharge to some extent. This was especially noticeable 

 in a striated positive column unless the strise were widely- 

 separated so that their dimensions were large compared with 

 the plates. 



Some of the results obtained are shown in figs. 9, 10, 

 and 11. 



Fig. 9 is for an almost dark discharge with only thin layers 

 of light at each electrode. 



i-o 



7 

 6 

 5 

 04 

 03 

 0-2 



Fig. 10. — Discharge in Oxygen. 

 Pressure 0*467 mm. Current 1*52 milliampere. 



mm 



^^-■-- ---J---4---J---1----I ^ bdrd_l - 







0-9 

 0-8 

 0-7 

 0-6 

 05 

 0-4 

 0-3 

 OZ 

 01 



II 12 13 14 



Fig. 10 is for an ordinary discharge with a uniform positive 

 column. The current between the small electrodes does not 

 vary as might have been expected from the known variation 

 of the electric intensity along such a discharge. The most 

 notable variation is in the Faraday dark space where the con- 

 ductivity is less than in the positive column, whilst the electric 

 intensity in the Faraday dark space is also much less than in 

 the positive column. Near the negative glow the conduc- 

 tivity rises, as we should expect from the small intensity 

 observed there, and falls again to a small value in the Crookes's 

 dark space. The conductivity near the positive electrode is 

 very small. 



