Prof. E. Edlund's Investigation of the Electric Light. 107 



Hence in the luminous arc the current performs a mechanical 

 work which is not compensated by the absorption of heat which 

 takes place there. 



We assume a voltaic battery of given electromotive force and 

 its poles connected by a solid conductor with a definite resistance. 

 The quantity of heat which is then produced by the current in 

 a given time is likewise determined. If now we assume that a 

 part of the solid conductor is taken away, and that in its place 

 there is aluminous arc between carbon points; suppose, fur- 

 ther, that its resistance is as great as that of the piece taken 

 away ; by this exchange the entire resistance in the circuit is not 

 altered. Yet the total quantity of heat produced by the current 

 must be smaller than that which can be calculated from the electro- 

 motive force and the resistance ; for now the current, aloug with 

 the production of heat, performs the mechanical work necessary 

 for detaching the material particles from the poles. This dis- 

 crepancy can only be removed if the intensity of the current is 

 diminished by so much that the diminution of heat thereby 

 produced exactly corresponds to this mechanical work. But 

 this mechanical work can only effect a diminution of the inten- 

 sity in two ways — either by its acting in a manner similar to an 

 increase of the resistance, or by giving rise to an electromotive 

 force which sends a current in the opposite direction to the 

 principal current. But now it is readily seen that if the requi- 

 site diminution of intensity is to be effected by an increase in 

 the resistance due to the mechanical work, this increase must 

 be of a different kind from an ordinary voltaic resistance. The 

 resistance caused by the work must be of such a kind that it 

 diminishes the intensity without the current producing a corre- 

 sponding quantity of heat in overcoming it. Assuming for a 

 moment that the resistance is of the ordinary kind and that we 

 designate it by m, the resistance in the entire circuit by M ; the 

 entire resistance while the voltaic arc lasts is M + m. If now 

 the voltaic arc be removed and the resistance made equal to 

 M-f-m by interposing a solid conductor, since the electromotive 

 force remains unchanged, the same quantity of heat must be 

 obtained as if the luminous arc existed ; and we cannot get out 

 of the dilemma which the assumption of an increase in the re- 

 sistance was intended to remove. Hence the resistance in ques- 

 tion, if its object is to be attained, must be of such a character 

 that it brings about a diminution in the intensity of the cur- 

 rent without causing a development of heat when the current 

 passes through it or overcomes it. Such resistances are not 

 yet known, and the one in question would be a resistance of a 

 new kind. How the required lowering of the intensity is really 

 brought about may be best seen from the three previously men- 



