VIBRATION OF FERROMAGNETIC WIRES. 7 



to the periodic vibration of the wire due to the magnetic change of 

 length. The positions of the maxima and minima were not, 

 however, materially changed by the length of the wire, or the tension 

 of the springs. In the case of iron, the magnetic change oî length 

 for the same field strength was small, so that the phenomenon was 

 not very marked. 



To study the phenomenon specially, we used another arrange- 

 ment ; the apparatus was the same as that described in the 

 preceding paper, used for the measurement of tlie magnetic change 

 of lenofth under constant tension. The wire to be tested was about 

 60 cm Ion"- and 0.4 mm thick : to the extremities of the wire, two 

 copper wires of nearly the same thickness were soldered. It was 

 hung vertically in the axial line of a magnetizing coil 80 cm long so 

 as to lie nearly in a uniform field, and to its lower end was attached 

 a weight, l^ear the lower end of the copper wire, a thin rotating 

 cylinder carrying a reflecting mirror was placed horizontally and 

 came in contact with a suitable pressure to the vertical wire. The 

 working of the arrangement was the same as in the preceding 

 experiment. 



The magnetizing coil was wound in 4 layers and gave a field of 

 26.0 C.G.S. units due to a current of one ampere. The coefficient 

 of self-indaction of the whole circuit was 1.66x10" cm and its 

 resistance 18.2 i>, so that the time oi relaxation was 9.1x10"* 

 seconds. 



With the above arrangement, we found also two marked maxima 

 in the amplitude of vibration for iron as well as for nickel, ihe 

 amplitude of vibration is plotted against the frequency of the current 

 in Figs. 1 and 2. In both cases, the maximum field during one 

 complete period of vibration is 28.5 C.G.S. units, and the weight 



