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



Both these experiments lead, therefore, to the result that D is 

 also independent of the electromotive force of the battery. 



Third Series of Experiments. 



7. In this series iron was used for the pole-points. It was 

 observed that the points became strongly oxidized, by which the 

 conduction in the arc was less and the intensity diminished, so 

 that it was difficult to obtain an accurate and trustworthy mea- 

 sure for the resistance of the luminous arc. Between two suc- 

 cessive experiments the oxide had to be removed with a file. 



The following numbers were obtained before a thick coating 

 of oxide had time to form. 



Experiment VI. The intensity was = Tg. 54° 15'. 



Length of the luminous arc =4 divisions. Resistance =3*4 



„ „ = 2 „ „ =2*8 



» » = I a a = 2*4o 



Experiment VII. The intensity was =Tg. 56° 25'. 

 Length of the luminous arc =4 divisions. Resistance =3*3 



The battery in both these experiments consisted of fifty Bun- 

 sen's elements. 



Fourth Series of Experiments. 



In this series carbon points were again used, yet of a different 

 kind to the former ones. The rheostat was emptied, cleaned, 

 and filled again with solution of sulphate of copper. 



Experiment VIII. The battery consisted of seventy-seven ele- 

 ments. When 0*6 inch of the rheostat was interposed in the cir- 

 cuit, the needle stood at 63° 43' ; and when thereupon thirteen 

 units were interposed, at 43° 53'. From this are calculated 

 M = 10 62 and E = 22'73. When 0-6 inch only of the rheostat 

 was in the circuit, and the length of the arc was =4 divisions, 

 the resistance was =6*7. 



For the same intensity there was obtained : — 



Length of the arc =3 divisions. Resistance =6*2 

 « =2 „ „ =5*9 



„ =1 „ „ =5*4 



Experiment IX. In this experiment twenty elements were taken 

 away, so that the battery only consisted of fifty-seven. When 

 there was 06 inch of the rheostat in the circuit, the deflection on 



