CHANGE OF ELASTICITY BY MAGNETIZATION. 



11 



in contact with the wire under suitable pressure, to prevent sliding. 

 The weight was dipped in w^ater so as to avoid its vibratory 

 disturbance. The magnetizing coil w^as so long that the bar lays 

 nearly in a uniform field. The measurement of the magnetic 

 elonoration jrave the followino; results ; — 



Soft iron. 



St«:' el. 



W^olfram steel. 



Nickel. 



Cobalt. 



ol 



Here H denotes the eifective field and -^ the elongation or 

 contraction per centimeter due to magnetization. These results 

 are also drawn in Fig. 2. The curves for soft iron, steel, and Wolfram 

 steel are quite ordinary ; that for nickel, which is not annealed, is less 

 steep than fijr ordinary annealed nickel. Professor Nagaoka and one 

 of us have already pointed out that the magnetic character of cobalt is 

 much affected by annealing. The curve for cobalt, which w^as well 

 annealed, shows this abnormity. We shall soon observe that the 

 elasticity of a substance undergoing large magnetic change of length 

 is also much influenced bv mairnetization. 



5. In observing the displacement of the image of the vertical 

 scale in the field of the observing telescope by passing a current 

 through the coils, w^e were struck with the large effect contrary to 



