56 



NA TURE 



[November 19, 189] 



maximum amplitude as the three equal harmonic alter- 

 nating currents dififering by 60° in phase, there will be 

 the same maximum variation in the number of ampere- 

 turns in the two cases. 



Mr. Dolivo Dolirowolski, the designer of the three-phase 



proportional to the magnetizing force ; secondly, from the 

 magnetic leakage in the motor being different when the 

 axis of the rotating field cuts the ring between two of the 

 coils, and when it passes through a coil conveying a 

 current, a case which cannot, of course, be neglected 



Fig. 20. — Three-phase alternate current motor (open winding) ; currents differing by 120° in phase, 

 and represented in direction ^nd magnitude by th; direction and length of the arrows. 



motor employed in the Lauffen-Frankfort transmission, 

 was the first to draw attention to this variation in the 

 number of ampere-turns with a rotatory magnetic field 

 motor, and the pulsation of the field thus produced. But 

 we venture to think that in his deductions he lays too 

 much stress on the mere variation in the number of 



when each coil occupies a considerable portion of the 

 ring, as in an actual three-coil motor. 



Hence we doubt whether it could be decided theo- 

 retically without experiment with which of the windings 

 indicated in Figs. 12 or 20 the rotating magnetic field 

 would undergo the greater variation in strength, if in 



\ / \ / \ / \ 



7^ i27 #^ 7 m-^ 



PiQ 23.— Three harmonic alternating currents of the same period and maximum 

 altitude, but differing by 120° in phase. 



ampere-turns, and too little on the fact that the variation 

 in the number of ampere-turns only imperfectly indicates 

 the variation in the strength of the rotating field. That 

 the one variation does not alone measure the other arises 

 first from the induction in iron not being, as is well known, 



NO. I 151, VOL. 45] 



both cases the windings occupied the whole of the iron 

 ring. 



Since, as we have proved, the algebraical sum of the 

 three alternate currents in the coils I, II, III, Fig. 20, is 

 always nought, Kirchhoff's second law suggests that these 



