ELECTRICITY. 93 



battery, rings consisting of fused globules of metal were 

 formed on the terminal plates ; in my experiments made in 

 attenuated media, alternate rings of oxidation and deoxida- 

 tion are formed. Thus, if the plate be polished, coloured 

 rings of oxide will alternate with rings of polished or unoxi- 

 dated surface ; and if the plate be previously coated with an 

 uniform film of oxide, the oxide will be removed in concen- 

 tric spaces, and increased in the alternate ones, showing a 

 lateral alternation of positive and negative electricity, or 

 electricity of opposite character in the same discharge. 



It would be hasty to assert that in no case can the electri- 

 cal disruptive discharge take place without the terminals be- 

 ing affected. I have, however, seen no instance of such are- 

 suit where the discharge has been sufficiently prolonged, and 

 the terminals in such a state as could be expected to render 

 manifest slight changes. 



The next question which would occur in following out the 

 enquiry which has been indicated, would probably be, What 

 is the action upon the gas itself? is this changed in any man- 

 ner? 



In answer to this, it must be admitted that, in the present 

 state of experimental knowledge on this subject, certain 

 gases only appear to leave permanent traces of their having 

 been changed by the discharge, while others, if affected by 

 it, which, as will be presently seen, there are reasons to be- 

 lieve they are, return to their normal state immediately after 

 the discharge. 



In the former class we may place many compound gases, 

 as ammonia, olefiant gas, protoxide of nitrogen, deutoxide 

 of nitrogen, and others, which are decomposed by the action 

 of the discharge. Mixed gases are also chemically combined : 

 for instance, oxygen and hydrogen unite and form water; 

 common air gives nitric acid ; chlorine and aqueous vapour 

 give oxygen, the chlorine uniting with the hydrogen of the 

 water. 



