CHANGE OF DIMENSIONS BY MAGNETIZATION. 91 



recovers. The field at which the tube returns to its former 

 length is not yet reached so far as the present experiment 

 extends. The result agrees qualitatively with that of Bidwell and 

 the calculation of Knott. 



The general form of the curve does not change by the 

 application of a constant longitudinal field, but the field of maxi- 

 mum contraction shifts into high field as the longitudinal field 

 increases. The amount of the maximum contraction increases 

 with the longitudinal field, till it reaches a maximum, and then 

 it gradually decreases. In weak circular fields, the change of 

 length diminishes with the increase of the longitudinal. 



14. As in the case of wolfram steel, three curves in dotted 

 lines are given in Fig. 9, two of which correspond to the change 

 of length at the temperatures of 18.7°C and 76.1° respectively. 

 When the key in the circuit of the circularly magnetizing coil 

 was reversed so as to produce a field, the change of length 

 corresponding to the third curve was obtained. 



The change of length by longitudinal magnetization at ordi- 

 nary temperature is somewhat less than those obtained by previ- 

 ous experimenters. The difference is probably to be ascribed to 

 the well annealed state^' of the tube ; also, the resistance to the 

 elongation experienced by the tube due to the friction of the 

 circular magnetizing coil was found to affect the result slightly. 

 The oeneral feature of the clianoe of leno;th is so well known 

 that farther remarks are unnecessary. It is only to be noticed 

 that here the field of the maximum elongation is greater by 20 

 C. G. S. units than that of tlie minimum contraction due to 

 circular magnetization. 



The rise of temperature is to diminish the change of length 



1) Bidwell. Phil. Mag. 55, 228, 1894. 



