108 Prof. E. Edlund's Investigation of the Electric Light. 



tioned cases, in which we know accurately what takes place. If the 

 current passes through a liquid chemical compound, a chemical 

 decomposition is set up in it. The work which the current 

 exerts in producing this decomposition, from our present point 

 of view, is quite analogous to the mechanical work required 

 in the voltaic arc for disintegrating the polar wires. In the 

 first case it is the attraction between different substances, and 

 in the latter the attraction between particles of the same kind, 

 which has to be overcome by the current in order to effect a se- 

 paration ; but this difference between the forces overcome in the 

 two cases can have no influence on the reflex action of the 

 work on the current itself. Now we know for certain that the 

 work of chemical decomposition performed by the current does 

 not diminish the intensity in such a manner as to increase the 

 resistance ; for this chemical work is quite compensated by the 

 absorption of heat which takes place in decomposition. We must 

 thence conclude that the disintegration of the pole-surfaces in 

 the luminous arc has also in this case no influence on the mag- 

 nitude of the resistance. Passing to the two cases mentioned 

 in which induction takes place, we find that the work produced 

 by the current is compensated by electromotive forces, and not 

 by the intensity being lessened by an increase in the resistance. 

 Since, then, in the three cases mentioned, the mechanical work 

 performed by the current is not compensated by the intensity 

 being lessened owing to increased resistance, we must assume 

 that the deportment in the fourth case must be the same, since 

 we can assign no valid reason for the contrary. In addition to 

 this, there is another reason, which must not be left out of sight. 

 It is known, from another branch of electrical science*, that the 

 disintegration of solids, by breaking, filing, scraping, &c, fre- 

 quently developes electricity. This would doubtless always be the 

 case if it were possible to remove the parts separated so quickly 

 from one another that the separated electricities had no time to 

 recombine. By the whole of this we are led to the conclusion 

 that in the electric light, by the mechanical disintegration of the 

 solid poles, an electromotive force is produced, which sends a current 

 in the opposite direction to the principal current. 



We shall now show how this conclusion agrees with expe- 

 riment. 



3. If an electromotive force is present in the voltaic arc, it must 

 of course remain constant and unchanged as long as the electro- 

 motive force of the battery, the intensity of the current, and the 

 resistance remain unchanged. It must therefore be indepen- 

 dent of the length of the arc, provided that, when the arc is 

 lengthened, so much of the other resistance is taken out that the 

 * Riess, Die Lehre von der Reibungselectricitcit, vol. ii. p. 400. 



