Crook — Electromagnetic Alternating Cur remits. 133 



Akt. XYII. — Demagnetizing Effects of Electromagnetically 

 Compensated Alternating Currents; by Zeno E. Crook. 



The effect on the hysteresis cycle of passing an alternating 

 current longitudinally through an iron wire, was given in a 

 paper published in 1891, by Dr. G. Fienzi and Professor G. 

 Gerosia.* At a later date, Ignas Klemenicic published a paper 

 on the relation of circular to longitudinal magnetism in iron 

 and steel wires. He made a very brief mention of the effect 

 due to alternating current. In the first named paper the 

 writers found a very evident reduction of the area of the 

 hysteresis cycle, and that a current of three amperes per sq. mm. 

 was sufiicient to totally destroy the hysteresis. When in this 

 condition, the ascending and descending magnetization curves 

 coincide and the effect of the magnetizing force approaches the 

 theoretical condition expressed by Frohlich's formula 



aH 



in which a and /3 are constants for a given specimen of iron, and 



— is the saturation value of I. The writers thous'ht the effect 



observed was due only to the demagnetizing power of the rap- 

 idly oscillating circular magnetic field. Their reason for this 

 was that there was no perceptible jarring or vibration in the 

 iron. 



An attempt will be made in this paper to go still further into 

 the study of the effects of alternating current on the magnetic 

 properties of iron and steel. The main object of the study 

 will be to discover if there is an effect due to the current inde- 

 pendent of that produced hy the circular mcignetism. 



The first question to be solved was how to eliminate the 

 electromagnetic action, so that the effect of the current alone 

 could be studied. This was done, approximately, by making 

 use of the principle discovered by Ampere, that when two 

 adjacent currents in parallel conductors flow in opposite direc- 

 tions, the external field of force of the one tends to destroy 

 that of the other. In order to be effective in destroying the 

 internal as well as the external magnetic actions of the current, 

 it was necessary to build up the iron from very thin laminae, 

 and send the current in opposite directions in each alternate 

 layer. 



*Eendiconti de Insfcituto Lombardo, vol. xxiv, fasc. x, April, 1891 ; Elec- 

 trician, April 3, 1891 ; Ewing, Magnetic Induction in Iron and Other Metals, 

 page 319 ; Wiedemann's Annalen, vol. Ivi, page 530. 



