Length of Ferromagnetic Substances hg Magnetization. 397 



The full lines represent the curves ol: the change of length 

 plotted against the internal tield (H' = H — LX); the dotted 

 lines refer to the external tield H. The comparison of the 

 corresponding carves shows us the influence of the demag- 

 netizing force. 



In the experiments at high temperatures the internal field 

 for a given magnetizing current varies with the temperature, 

 as the intensity of magnetization changes with it. A full 

 knowledge of the field in which experiments were carried on 

 requires the determination of the intensity of magnetization 

 at each temperature and field. Since our experiments did 

 not extend so far the curves of the length-change at different 

 temperatures were drawn for the external field. But if we 

 refer to fig. 3, it is easy to see how the forms of these 

 curves are to be changed if the internal field be used instead 

 of the external one. 



SicheL — The chano-e of length in nickel under hio-h and 

 low temperatures is graphically shown in fig. 4. The 

 temperature markedly reduces the magnetic contraction 

 of the metal. At a temperature of 240^ C. the contraction 

 in H = 800 is already reduced to half its ordinary value, and 

 at 400° C. it almost vanishes. With the ovoid of the same 

 specimen Prof. H. Xagaoka and Mr. S. Kusakabe found the 

 'critical temperature to be 400° C. In liquid air the con- 

 traction is reduced in weak fields, but is increased in strong- 

 fields. The relation between the chancre of length and the 

 temperature for given external fields is given in fig. 5. 

 Each curve has a minimum point_, the temperature of 

 which decreases as the field is increased. We also notice 

 that the contraction vanishes asymptotically as the tem- 

 perature approaches to 400° C. It is to be remembered 

 that on account of the demao-netizino- force each curve 

 does not represent the contraction in a constant effective 

 field, but shows the general feature of contraction with re- 

 gard to temperature. The above results are consistent with 

 the former experiments. 



Sojt iron. — The change of length in soft iron is given in 

 fig. tJ. 



As the temperature is raised the contraction in high fields 

 gradually disappears, and at 312° C the change of length is 

 similar to that of tungsten-steel at ordinary temperature. 

 With further increase of temperature the elongation, after 

 passing a maximum, gradually decreases. We could trace 

 the elongation up to 970° C, which is far higher than its 

 critical temperature. The effect of cooling by liquid air is 



