410 C. Bar us — Torsional Magnetostriction in Strong 



If this condition were dropped the model, though still avail- 

 able, would lack simplicity. 



The effect of longitudinal magnetization as inferred from 

 the axial setting of the revoluble magnets, is increased tension 

 along the fibers and therefore a corresponding increase of the 

 horizontal component in question. Rigidity is apparently- 

 increased under all conditions, as is inferred from the distribu- 

 tions given in figure 2, type I. My own measurements* in 

 addition to the more recent experiments of Mr. H. Day,f in 

 which strong fields were applied, show an invariable incre- 

 ment of rigidity, increasing towards a limit as the Held strength 

 increases, and greater as the diameter of the rod is smaller. 

 All this would be suggested by the model, remembering that 

 slip takes place on twisting when the obliquity;}: of the external 

 fibers has reached a fixed quantity. 



If the increment of rigidity due to longitudinal magnetiza- 

 tion were to be associated with the Joule effect of magnetic 

 elongation, one would expect a change of sign corresponding 

 to the march of the latter in an increasing field. Rigidity how- 

 ever is a regularly increasing quantity and shows no change of 

 sign of the kind in question ; and this is just what the model 

 indicates. Again for the case of nickel in which the Joule 

 effect is at the outset opposite in sign to that of iron, the effect 

 of longitudinal magnetization is nevertheless increased rigidity. 

 An example of these results will be found below, §6. Figure 

 2, type I, is an extreme case. One may note that the poles of 

 the magnets are closer together than the molecular centers, 

 either longitudinally or laterally. 



The effect of transverse magnetization, if the hypothesis of 

 lines of stress relatively far apart be retained, is given as one 

 extreme case by type II of figure 2. The molecular magnets 

 tend to lie across the lines of stress and rigidity is therefore 

 diminished. From the geometry of the figure, however, it 

 appears that the poles of the molecular magnets now lie much 

 farther apart than in case I. Hence the transverse effect should 

 be a decrement of rigidity, under like circumstances of much 

 smaller numerical magnitude than the increment of rigidity 

 due to the longitudinal field. Thus transverse magnetization 

 is adapted to test a variety of phenomena, and it seemed to me 

 that an examination of these in very intense fields (much more 

 intense than are available for longitudinal magnetization) might 

 throw new light on the nature of magnetostriction. 



The case of circular magnetization I had hoped to omit, as 

 it was studied at considerable length by the original inves- 



* Bams; this Jour., (3), vol. xxxiv, p. 175, 1887. 

 \ Howard Day: this Jour., (3), vol. hi, p. 449, 1897. 

 \ Barus: 1. c, pp. 182-183. 



