626 SCIENCE PROGRESS 



objection to this view is that it offers no explanation of the 

 fact that the molecules of the gas must penetrate to the surface 

 of the cathode (probably conveying positive charges to it) 

 and there interact with carbon atoms instead of waiting till 

 the latter have proceeded some distance from the cathode, 

 for it is well known that an arc can only with great difficulty 

 be run in an atmosphere which does not readily form a chemical 

 compound with the material of the pole. 



Dr. Dufneld regards the interaction of the gas molecules 

 with the carbon as playing a very important role in the 

 mechanism, and that, while permanent chemical compounds 

 are probably not formed in such a high-temperature region as 

 the arc, yet there may be momentary interaction between 

 carbon and gas atoms rendering the electronic content of the 

 former atoms unstable and causing them to yield up some 

 of their store. There are of course many ways in which the 

 yielding of the electrons could take place. Thus the atom 

 might eject the four electrons obtained from the current supply 

 under the influence of thermionic or photo-electric action and 

 subsequently be liberated uncharged, or the carbon atom 

 could be detached from the cathode by interaction with the gas 

 and the four electrons liberated at the same instant ; or in 

 the latter case only two electrons might be liberated, and, say, 

 one positively charged (divalent) oxygen atom might arrive 

 at that instant and form uncharged carbon monoxide ; or no 

 electrons might be liberated and uncharged carbon dioxide 

 formed. 



Prof. Dufneld inclines to the Thomson theory for other 

 reasons also. Carbon has not been found free with four 

 electronic charges ; and further there is the fact that Duddell 

 has located the back E.M.F. of the arc at the surface of the 

 anode and this seems to require negative, i.e. electronic, emis- 

 sion rather than positive there. Hence the author is anxious 

 to retain the electronic view and is at pains to point out that 

 electronic emission in some of the ways mentioned above is 

 just as compatible with the facts as Fleming's early view which 

 regards the emission as being atomic or molecular. 



