The Back Electromotive Force. 



139 



On the True Resistance and on the Back Electromotive 

 Force of the Electric Arc. By Julius Frith, 1851 

 Exhibition Scholar, The Owens College, Man- 

 chester. Communicated by Arthur Schuster, F.R.S. 



{Received March i^th, i<$95-) 



The following research on the true resistance of the 

 electric arc was carried out in the Electrical Laboratory of 

 the Owens College under the direction and with the 

 occasional assistance of Mr. Lees, Senior Demonstrator and 

 Lecturer of the Owens College. 



The question of the real resistance and the allied 

 problem of the back E.M.F. of the arc has received the 

 attention of several investigators, most of whom have 

 attempted to determine the value of the back E.M.F. if it 

 existed, by measuring the true resistance of the arc. 



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n-e^www 



R 



— 'I'J'I'H'I 1 ! 1 



I I I I I I I 



Fig. 1. 



A and B represent arc lamps. 



„ a battery of cells. 



E 

 C 

 R 



S 



w 



an ammeter. 



resistances. 



a switch to bring the points A and B to 

 the same potential. 



Wheatstone's bridge to measure the re- 

 sistance between A and B. 



K 



