134 



angular frame. In this frame slid a 

 cross-bar e' /, and within an inner slide 

 a b g h, a carrier through which was 

 pivoted, on a vertical axis, an integrating 

 roller. The angular position of this roll- 

 er was fixed by a rod k e, sliding at e 

 through a pivot e, free to move round in 

 a horizontal plane. The whole frame 

 could only move in a direction parallel to 

 the axis of sc, being constrained by guides 

 or rollers. Through the bar e' f at m 

 passed a pointer. Let x t y t be co-ordi- 

 nates of a point on the curve of primary 

 electromotive force, let x y be co-ordi- 

 nates of the curve traced by the non- 

 slipping integrator roller. Then by the 

 construction of the apparatus the follow- 

 ing relations held good. The roller was 

 always tangential to the curve x y, and 



ax me 



Let the scale of y be such that y 



V* T 



— _, and let m e = _, where L and R 

 R R' 



were coefficients of self-induction and 

 resistance. 



