CHANGE OF DIMENSIONS BY MAGNETIZATION. 97 



tlie expression — j^, or numerical calculation of it for different 

 values of / and t from the experimental curve of the ordinary 

 change of length leads to the conclusion that for iron, steel 

 and nickel, all the points, which we have remarked in connection 

 with the curves shown in Figs. 1, 4, 5, 7, 8 and 10, are involved 

 without exception in the expression of — ^/— • 



It may be observed that the behaviour of cobalt with regard 

 to the change of length is just the reverse of that of iron, and 

 therefore every result which we have obtained for iron is also 

 applicable to the case of cobalt, provided the sign of the length 

 change be properly reversed. Thus in strong fields, the length 

 of a cobalt tube should, by the combined eftect of longitudinal 

 and circular magnetizations, become shorter than when acted 

 upon by the former alone. In weak fields, the result should be 

 just the opposite. The field of maximum contraction should 

 increase with the circular, and the amount of the contraction, after 

 reaching a maximum, gradually decrease. The circular field at 

 which the maximum contraction occurs should be far greater 

 than that for iron. 



19. The comparison above made is qualitative ; how the 

 calculated and the experimental numbers agree with each other 

 is seen from the following table : 



