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



The electromotive force which is produced in the luminous 

 arc diminishes the intensity by an amount corresponding to an 

 interposed resistance of 6*7 nnits of resistance. From this we 

 may easily calculate the magnitude of this opposing force ex- 

 pressed as electromotive force of the battery. If the latter be 

 denoted by E and the electromotive force in the luminous arc 

 by D, we have 



E E-D 



1 2-285 + 8-4= 20-685 ~~ 20685 -67= 13-985* 



from which we obtain D = 0*3239 E. 



Experiment II. When the resistance M was increased to 

 14*176 units, and ll'O units of the rheostat were interposed in 

 the circuit, the intensity was =Tg. 45° 30'. The following re- 

 sults were obtained with this intensity : — 



Length of the arc = 3 divisions. Resistance =10'4 



» a " }> j) — 9*o 



1 — 9-2 



For this intensity we have thus + 36 = 10-4, # + 26 = 9"8, 

 and « + 6 = 9*2, from which # = 8'6 and b = 0'6. 



Calculating D in the same manner as in the preceding expe- 

 riment, we have 



D =0-3416 E. 



Experiment III. In this experiment M was made = 21*29 

 units. When 13*5 inches of the rheostat was inserted in addi- 

 tion, the tangent-compass indicated 36° 22' in the mean. The 

 entire length of the rheostat was 13*5 inches ; so that, retaining 

 the value mentioned for M, the intensity could not have been 

 made smaller by means of the rheostat. When the length of 

 the luminous arc amounted to 2 divisions, the deflection of the 

 galvanometer was 33° 40'. From this the resistance in the lu- 

 minous arc may be readily calculated. For we obtain : — 



Length of the arc = 2 divisions. Resistance =16-66 

 „ „ =1 „ „ =14-76 



We thus obtain, since the intensity is = Tg. 33° 40', a + 2b = 16*66 

 and a + b = 14*76, from which a = 12*86 and 6 = 1*9. 



From this we obtain, in the same manner as the first experi- 

 ment, 



D = 0*3336 E. 



5. It results from the preceding experiments that the electromo- 

 tive force D in the luminous arc is independent of the intensity of 

 the current, and that the essential resistance of the luminous arc is 

 proportional to its length, and increases as the intensity diminishes. 



