Pupin — Resonance Analysis of Alternating Currents. 477 



comparatively small share to the strength of the harmonic. 

 The third series showed that the harmonic appears in the 

 secondary of an open magnetic circuit transformer although 

 considerably weaker, but does not appear there to any appreci- 

 able extent when the magnetic circuit of the transformer is a 

 closed one. 



To the four conclusions given at the end of the series of 

 experiments under group A the following additional conclu- 

 sions may, therefore, be added : 



V. An alternator with slotted core armature produces a 

 complex harmonic electromotive force in which the upper har- 

 monic of three times the frequency of the fundamental is 

 generally by far the strongest. 



VI. The amplitudes of the fundamental and the harmonic 

 increase at the same rate with the increase of excitation • this 

 rate is within the limits of magnetization mentioned above 

 proportional to the excitation, that is to say, proportio?ial to 

 the magnetization of the armature. 



VII. A ferric inductance in circuit with a slotted iron core 

 armature introduces no new harmonics. It strengthens those 

 already existing in the electromotive force, that is odd har- 

 monics, especially the first odd harmonic. 



The same conclusions will evidently hold true for alter- 

 nators of ordinary types whose armature is made up of coils 

 wound on iron cores which are bolted to a cylindrical iron 

 drum common to all of them. 



High degrees of magnetization of the transformer core pro- 

 duce a strong deformation of the primary current wave. With 

 inductions of over 12000 C. Gr. S. lines of force per sq. cm. it 

 is possible to make the amplitude of the 1st odd harmonic 

 even greater than the amplitude of the fundamental. It is 

 evident, therefore, that the parallelism of the lines in fig. 5 

 ceases as soon as the magnetization curve of the transformer 

 core begins to approach the knee. Experiments relating to 

 this point will be described in the near future. The experi- 

 ments described in this paper were limited to conditions met 

 with in the operation of commercial alternating current appa- 

 ratus. 



V. Effect of the load upon the harmonics. 



It is a well known fact that the distortion of the primary 

 current disappears gradually with the increase of the secondary 

 load, that is when the external part of the secondary circuit is 

 a non-self-inductive resistance. The question arises now, what 

 becomes of the harmonics which produce the distortion of the 



