Electro-Motive Force and Current Curves. 155 



The lag in the first term of last three curves is 22°, 34 , 

 and 66° respectively. From the formula 



Tan d = Lp 

 R 



where 6 = angle of lag 

 p = 2im 



n = alternations per second 

 L = self-induction 

 R = told resistance in circuit 

 the self-induction may be calculated as follows : — 

 tan 2 2 = *4 



— ^? = # oi74 secohms. 



2^75 



tan34° = -67 



.\L=-67xcr43 



•0134 



2V75 



tan66° = 2*25 



.*.L= 2*2* X 2'AT. ;. 



— ^ zP = -on6 „ 



2^75 



These show that the self-induction of the armature 

 decreased with the increase of magnetization of the iron in 

 the cores. This agrees with the results of measurements of 

 the self-induction carried on in the ordinary way with the 

 machine at rest. These give, 

 with the fields not excited, 



L = -02 secohms ; 

 with the fields excited, 



L = "013 secohms. 



On taking power from the machine the irregularities 

 die out of the curve, and it becomes first nearly straight 

 from the maximum in one direction to the maximum in 

 the other, and then gradually approaches the sine curve. 



Electrolyte. — Next a copper-plating bath, consisting of 

 two plates of copper 30cms. x 40cms., placed ioocms. apart 

 in an acid solution of copper sulphate, was put in circuit, 

 and a current of 10 amperes was passed through. 



