Dimensions caused by Magnetization in Iron. 4:65* 



The first curve given (fig. 2) serves to illustrate the form 

 taken by several change of length cycles going up to different 



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field-strengths. Their character was first discovered and dis- 

 cussed by Nagaoka. It will be seen that the specimen which 

 is lengthening as the field is being increased, continues to 

 lengthen when the field is gradually withdrawn (except in the 

 very smallest cycle), then a maximum length is reached and 

 shortening begins and continues till the field is entirely removed 

 and put on in the opposite direction with sufficient strength 

 to drive out the residual magnetism. As the field is further 

 strengthened the specimen is magnetizedin the reverse direction 

 and begins to elongate again. We may roughly distinguish 

 four classes of cycles dependent upon the limits between which 

 the field is varied. First, in very low fields, two or three O.G.S. 

 units, there is no change of length; so the cycle is simply a hori- 

 zontal line. Second, from these fields up to about ten units the 

 length begins to decrease on diminishing the field, after having 

 remained constant just at first. Thirdly, we have the cycle 

 already alluded to in which increase of length takes place on 

 reducing the current, even though the length had been pre- 

 viously increasing with increasing current. And, fourthly, in 

 fields so great that the maximum length has been reached and 

 the specimen has then considerably shortened, on decreasing 

 the field again there is a loop on the lower side of the original 

 curve (not shown in curve given). 



The two curves given in fig. 3 bear on a point that has 

 been several times brought up, namely, whether the actual 

 thickness of the specimen has any effect on the change of 

 length. It is natural to assume that it has not, as these 

 curves o-o to show, provided the condition of "endlessness" 

 in the specimen is fulfilled to a sufficient degree ; but refer- 

 ence to a paper by Lochner (Phil. Mag. vol. xxxvi. p. 498) 



