60 



the field 1.73 ohm. The bank of trans- 

 formers, with its load of resistances, was 

 next switched on, and the latter so reg- 

 ulated as to give an armature current of 

 10 amperes at different degrees of excita- 

 tion. The dynamic characteristic marked 

 " 10 amperes " in the diagram was thus 

 found. Similar experiments were made 

 to obtain the characteristics at 20 and 30 

 amperes, which are also shown. Either 

 of the three dynamic characteristics can 

 now be used to determine, by the aid of 

 diagram Fig. 7, the coefficient of self- 

 induction of the armature ; and, if it 

 were not for certain disturbing causes, 

 the three coefficients thus obtained 

 should be identical. In reality, this is, 

 however, not the case, chiefly because 

 the impressed electromotive force is nol 

 a true sine function of the time. There 

 is also another disturbing element, 

 namely, the demagnetizing influence of 

 the armature current upon the field. 

 When the machine is working as a gene- 

 rator, the poles developed in the arma- 

 ture by the current itself are of the same 



