670 MR JAMES RUSSELL ON 



complete cycles, the B x component due to E^ kept at a constant value responds and 

 passes through a series of changes in the process of likewise becoming strictly cyclic. 

 The changes which take place during this preliminary transition period depend upon 

 the previous magnetic history of the iron and the well known molecular vibrational 

 effect due to the superposed reversals. If the amplitude of the H 2 reversals are below 

 the critical value required to practically wipe out the effects of hysteresis due to H^ no 

 further apparent change is produced after the first superposition (a relatively large 

 effect) followed by a few reversals of H 2 . The values of B x at the extremes of the 

 superposed reversals having become final, the molecular ' accommodation ' which still 

 goes on is cyclic. 



The B x component due to H^ kept at a constant value follows at least approximately 

 the changing permeability impressed upon the iron by the superposed alternating force 

 H 2 . The minimum values of B x occur at the extremes of the H 2 reversals, and the 

 maximum values of B ± when B 2 is changing most rapidly with respect to H 2 or when 

 eZB 2 /c£H 2 is a maximum. The maximum and minimum values of the B x induction 

 component thus occur twice during one complete reversal of H 2 ; in fact, the cyclic curve 

 closely resembles the curve which represents the changes produced in the magnetisation 

 of an iron wire when repeatedly twisted first in one direction and then in the opposite 

 direction. 



The B 2 induction component at the extremes of the H 2 reversals, and the maximum 

 values of the permeability (dB 2 /dH 2 ) which occur during these reversals, are both some- 

 what reduced in comparison with the normal B-H complete cycle when H x is not acting. 

 Also, if the values of H x be unduly increased, a lop-sidedness of the superposed B 2 -H 2 

 cycle results. 



III. — Magnetic dEolotropy of Demagnetised Iron. 



During the early stages of induction, iron is more permeable to a reapplication of a 

 magnetising force in the same direction (positive or negative), as that used in the 

 immediately preceding process of demagnetising by decreasing reversals, than it is to a 

 force (positive or negative) at right angles to that used in the immediately preceding 

 demagnetising process. For the two samples of iron used this difference is of the 

 order of 30 per cent., but vanishes as the magnetising force is increased. By assuming 

 that the deflecting force H is proportional to the cosine of the angle which H makes 

 with the magnetic axis of any stable molecular group, a possible explanation of the 

 general nature of the effect is afforded. 



Iron left with residual polarity due to a force at right angles to that subsequently 

 applied is more 'permeable during the early stages of induction, and iron demagnetised 

 by a force at right angles to that subsequently applied is less permeable during the 

 early stages of induction, than iron magnetised under normal conditions. This com- 

 parison has an obvious bearing on the molecular condition of demagnetised iron. The 

 subject is being continued. 



