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



tional to the square of the electromotive force divided by the 

 entire resistance of the circuit. This holds good so long as the 

 current performs no other work than the production of heat. 

 That this law deduced from experiment is correct may be re- 

 garded as proved, since, as Clausius has shown*, it may be 

 theoretically deduced. But if the current at the same time that 

 it produces heat performs other work, the quantity of heat de- 

 veloped must be diminished by an amount corresponding to this 

 work. Hence, if we have a voltaic battery of given electromotive 

 force, whose poles are joined by means of a solid conductor, and 

 if besides the electromotive force we know both the internal and 

 external resistance of the battery, the quantity of heat developed 

 during a certain time may easily be calculated. Assume, now, 

 that part of the external resistance is removed, and in its place 

 is inserted a decomposable liquid (dilute sulphuric acid for in- 

 stance) the resistance of which is equal to that part of the solid 

 conductor which has been removed, by this exchange the elec- 

 tromotive force and the resistance will have undergone no alte- 

 ration. Yet the heat produced cannot be so great as before, 

 since the current, along with the production of heat, performs 

 the mechanical work necessary for chemically decomposing the 

 water. This is due to the circumstance that, when water is de- 

 composed into hydrogen and oxygen, there is an absorption of 

 heat, and that this absorption is equal to the heat produced 

 when hydrogen combines with oxygen. Hence the absorption 

 furnishes a measure of the work necessary for the decomposi- 

 tion. The entire quantity of heat produced by the current will 

 be diminished by an amount which corresponds to the work of 

 decomposition effected by the current. The coating of the elec- 

 trodes with hydrogen and oxygen, by which is produced a cur- 

 rent in the opposite direction to the principal one, is an entirely 

 secondary phenomenon which has nothing to do with the essence 

 of the case. 



Further, if we have a voltaic current whose total resistance is 

 known, and whose intensity is continually changing, the total 

 heat produced by the current can be calculated if the intensity 

 at each moment is known. If a closed circuit be placed in the 

 neighbourhood of the principal current, an induced current is 

 developed in it. The primary current produces voltaic induction 

 simultaneously with the production of heat ; and it is clear that 

 the production of heat must be less than when there is no in- 

 duction. But, on the other hand, the electromotive force of the 

 battery and the resistance of the principal conductor, on which, 

 in accordance with the law mentioned above, the production of 



* PoggeudorfF's Annalen, vol. Ixxxvii. p. 415. 



