Brown — The Subsidence of Torsional Oscillations. 



527 



In a final test the wire was onoe more taken down and heated twicQ to a 

 very bright cherry red, so as to make it as soft as possible, and wlien cold its 

 rigidity was measured and found to be about 715 x 10'' grammes per sq. cm. 

 It was again put into the solenoid, and tested in the same way as before for 

 the subsidence of torsional oscillations. The wire in this soft state was not 

 tested for fatigue, because the fatigue is extremely small even for a prolonged 

 application of the alternating magnetic field. The results for the subsidence 

 of torsional oscillations when magnetic fields of tliree different frequencies 

 were applied are given in Table V, and some of tliem are shown as curves 

 in Fig. 2. 



Table V. 

 Rigidity ^ 715 x 10' grammes per sq. cm. 



Tables IV and V show tlie great change in the damping of torsional 

 oscillations in the magnetic field due to a small change in the rigidity of the 

 wire. Taking a mean of tlie two values of tlie amplitudes of the 70th 

 oscillation in the last two tables, and comparing it with the corresponding 

 value in Table III, we find that for a decrease of about 8 per cent, in the 

 rigidity the amplitude of the 70th oscillation is decreased about 80 per cent, 

 in the D. C. magnetic field, and for an A. C. magnetic field of the same value 

 at a frequency of 50 per second the 70th amplitude has increased only about 

 10 per cent., and for the A. C. field at frequency 250 the increase is about 

 20 per cent. 



