516 Variation of Electric Intensity in Rarefied Gases. 



Fig. 11 shows the variations in the conductivity in a striated 

 positive column. 



Fig. 11. — Discharge in Air. 

 Pressure O30 mm. Current 1*03 milliampere. 



0-cO 



0-15 



010 



005 



! 











1 





| 





















































/ 

























/ i 



/ | 



/ 



/ 



















y 



.-'*: 



015 



0-/0 63 



12 3 4-567 



05 



9 10 II 12 13 14-cws 



The conductivity falls between the striae apparently instead 

 of rising, as the intensity-curves lead one to expect. It is 

 very probable that the radiation which the discharge emits 

 may produce ionization on the small platinum electrodes, 

 which would increase the apparent conductivity of those 

 parts of the discharge which emit radiation. Thus the nega- 

 tive glow and the luminous parts of the positive column 

 conduct better than the dark parts of the discharge. 



The fall in the conductivity near the positive electrode pro- 

 bably corresponds to the increase in the intensity which 

 usually occurs there before the drop to zero close to the 

 electrode. 



In conclusion, I wish to say that my best thanks are due 

 to Prof. J. J. Thomson for valuable suggestions and advice 

 during the carrying out of these experiments at the Cavendish 

 Laboratory. 



