510 Jf. [. Pv/pin — Electrical Oscillations of 



Let P„ = amplitude of the potential difference in the secondary 

 condenser, then 



P„ = pN 7 =z * =. (15) 



A//> 9 L a S 9 + (/? 9 M s + RS) s 



When R 2 is small in comparison to p*JJ and p*M* is small in 

 comparison to p 2 U$* then 



^ M E 

 P 2 = i>Nj- g (16) 



which is the same in form as relation (8) in the preceding 

 paper * 



These relations differ very little from those in (10) and (11) ; 

 hence curves tig. 1 and fig. 2 will apply to this case also. 



The theory of low frequency resonance in mutually inductive 

 circuits when the impressed e. m.f. is a complex harmonic is of 

 no importance in connection with experiments in which the 

 impressed electromotive force is generated by an ordinary alter- 

 nating current machine, because the upper harmonics, as will 

 be seen presently, are almost entirely absent then. When the 

 alternating current is produced by transforming an interrupted 

 current, then, since in this case the currents employed are 

 small and therefore the iron cores but slightly magnetized, the 

 harmonics are incomparably more persistent. 



I prefer to discuss first those experiments in which circuits 

 with iron cores subject to considerable magnetizations are 

 employed, and where a marked difference exists between 

 theory and experiment because the behavior of iron is so 

 peculiar then and so strongly brought out by resonant circuits 

 that these experiments appeared to me of much greater im- 

 portance than the experiments with circuits without iron which 

 circuits, having no hysteresis losses, bear more directly 

 upon the theory of what may be called Ideal Low Frequency 

 Resonance. 



Description of Experiments. 



The alternator was a 1 H-P machine consisting of a Gramme 

 ring armature with 16 poles, such as is used in the Crocker- 

 Wheeler motors. Its field magnet consisted of a cast iron ring 

 with sixteen pole-projections. The field was separately excited. 

 The armature rotated at the rate of about 2810 revolutions per 

 minute, the e. m. f. had therefore about 375 periods per second. 

 The amplitude of the impressed e. m. f. was about 600 Volts. 

 The primary poles cd (fig. 3) of an induction coil were con- 

 nected to the poles of the alternator. The primary of this coil 

 consisted of 3000 turns of No. 20 B. & S. W. G. wire having a 



* See this Journal, May, 1893, p. 426. 



