under the Influence of the Electric Discharge. 421 



It is possible that a first fraction of the electricity transmitted 

 is used up in producing an increase of the mean temperature 

 resulting from a transformation of oscillatory motion, that by 

 this an unstable condition of the molecule is brought about, 

 and the remainder of the electricity completes the decompo- 

 sition. 



There is a remarkable parallelism between the production 

 of heat caused by a ray of light in a feebly absorbing medium 

 and that which is caused by the electric discharge. 



(1) If a conically enlarging beam of light propagate itself 

 in a feebly absorbing medium, the quantity of heat developed 

 is nearly the same in every section of the beam ; in the same 

 way the heat produced by an electric discharge is the same in 

 each section. 



(2) If we increase the intensity of the ray of light, but allow 

 it to pass for a proportionately smaller time, an equal quantity 

 is absorbed in the two cases ; the same holds good for the dis- 

 charge when we increase its strength, but decrease its fre- 

 quency. 



(3) If we increase the optical absorption by, for example, 

 increasing the number of absorbing particles in the absorbing 

 solution, the quantity of heat produced is increased in propor- 

 tion ; so also the electric evolution of heat in a gas becomes 

 greater for the same section as the pressure increases. 



It seems therefore very probable that the absorption of 

 energy in both cases follows in the same way, that therefore 

 the discharge consists in a propagation of vibrations which 

 give up a portion of their energy to the gas-molecules. But 

 then we must make the assumption that the amplitude caused 

 by a quantity of electricity e is proportional not to e, but 

 to s/ e. 



But even under this assumption the phenomena of the elec- 

 tric discharge cannot be explained so well as the optical phe- 

 nomena, since so many disturbing causes occur. 



Amongst them must be mentioned, first of all, the statical 

 charge of the glass walls, which largely affects the transmitted 

 discharge, and produces by itself a definite polarization of the 

 gas-molecules, sometimes increasing and sometimes diminish- 

 ing the energy given up by the discharge. These exterior 

 charges produce most effect with wide tubes, in which the 

 motion produced by the discharge itself is much less rapid than 

 in narrow tubes. Here should be mentioned the interesting 

 fact discovered by Hittorf, that a gas which is traversed in 

 one direction by a discharge conducts the current in a direc- 

 tion at right angles to that much better than when this is not 

 the case. 



Phil Mag. S. 5. Vol. 10. No. 64. Dec. 1880. 2 II 



