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XVII. The Effect of Electrical Oscillations on Iron in a 

 Magnetic Field. By W. H. Eccles, D.Sc., A.R.C.S* 



THE following investigation of the action of high-frequency 

 oscillations upon iron held magnetized in a magnetic 

 field was carried through in July and August of last year, 

 and was undertaken to supplement in a quantitative manner 

 the rather vague information available. Since Marconi f 

 announced in 1902 that feeble electrical oscillations were 

 capable of altering the flux of induction in a piece of mag- 

 netized soft iron, a great deal of work has been done in the 

 endeavour to determine what it is that really happens in this 

 process. A glance through the chronicles of these labours 

 reveals a surprising lack of precise data, and shows, in fact, 

 that most of our knowledge of this subject is merely quali- 

 tative. This is due, no doubt, to the complicated possibilities 

 accompanying any experimental method that can be devised. 

 One, for instance, among these difficulties, is the shielding of 

 the greater mass of an iron wire, or other sample, by the eddy 

 currents that are generated in the metal by the oscillations. 

 This skin-effect was, in a way, overcome by Maurain by using 

 oscillations sufficiently vigorous to penetrate to the very core 

 of the iron or steel wire experimented upon. By this means 

 he has shown that if the I H curve of a sample be drawn in 

 the ordinary manner while these very vigorous oscillations 

 are in operation, the curve obtained is not looped but is the 

 single path obtained by the coalescence, as it were, of the 

 branches due to increasing and decreasing fields. The single 

 curve thus obtained he called, after Duhem, the "normal 

 curve of magnetization." Duhem had previously shown from 

 thermodynamical reasoning that the effect of a long train of 

 slowly damped oscillations superposed on iron at any stage of 

 the cyclic process would be to bring the representative point 

 on the I H diagram towards a unique locus — a locus, he con- 

 cluded, exactly the same as that obtained by mechanicallv 

 agitating the iron throughout the cycle. This theory of 

 Duhem's takes no account, of course, of the shielding of the 

 inner parts of the iron from the action of the oscillations ; 

 and thus cannot be demonstrated experimentally except by 

 using, as Maurain J has done, very powerful oscillations. 



In the experiments to be described, an endeavour has been 

 made to turn the difficulty arising from the skin-effect. 

 Oscillations so feeble have been used that they affected only 



* Communicated "by the Physical Society : read June 22, 1906. 

 t Hoy. Soc. Proc. lxx. p. 341, July 1902. 



J Maurain gets slightly different curves by mechanical agitation and 

 by oscillations. 



