728 



INDUSTRIAL APPLICATIONS. 



we have (1272) 



W 



(3) 

 (4) 



r=i 



y 



X _ X 



^ y 



b + x 



Drawing the right line L (Fig. 259), defined by equation (i), in 

 which we take as co-ordinates the numerical values of-* and of y, we 



take CQ = #, draw the vertical QN, and join CN. The point M, at 

 which this right line cuts the characteristic curve, gives the electro- 

 motive force E lf and from equation (3) we have 



The condition tx = I'b (4) shows also that if we take QB = b, and 

 join CB, the current / is represented by n x PF. Finally, the total 

 current is I = 



In order that the intensity / of the current shall be independent 

 of the resistance X, the ratio must be constant that is to say, 

 the characteristic curve must be a right line parallel to L. 



