r " Electric Discharge in rarefied Hydrogen and Oxygen. 303 



Table X. 



V- 



Y. 



93 



SO 



4-5 







21 



40 



1.05 



25 



•65 



15 



. _ ___ 







It must be observed that the theory that, with a given 

 pressure and current, the force in the positive column is 

 independent of its length, necessitates the conclusion that 

 extremely few positive ions are generated within it in com- 

 parison with the number of negative ions that traverse it. To 

 make this obvious, let us suppose that a negative ion by 

 collision breaks up one molecule into ions in going through 

 the positive column which is 5 cms. long, so that half the 

 current is formed within the positive column. Then, if the 

 positive column were doubled in length, the force within it 

 remaining the same, the passage of a negative ion through it 

 would give birth to 3 other negative ions, so that J of the 

 current would originate within the positive column. In that 

 case, if the circumstances of the discharge outside the positive 

 column were unchanged, the current would be doubled, 

 instead of remaining the same. Similar reasoning shows 

 that if greatly to extend the positive column does not sensibly 

 affect the force in it, a sensible proportion of the ions which 

 traverse it cannot have been generated in it by collision. If 

 then there is no anode fall of potential where positive ions 

 might be generated, we conclude that comparatively few 

 positive ions pass through the positive column ; and otherwise, 

 that all but a small percentage of the positive ions within it 

 have to pass through its whole length. 



Estimation of the Chemical Action per centimetre of the 

 Positive Column. 



I have discussed the theory of the positive column with 

 reference to the curves of fig. 3, before estimating the che- 

 mical action per centimetre of the positive column by means 

 of the curves of fig. 2, because the curves of fig. 3 enable us 

 to interpret those of fig. 2. Their relation is well illustrated 



