218 Scientific Proceedings^ Royal Dublin Society. 



Table I. 



If we plot these results in the form of curves, with the numbers in the 

 first column as abseissse, and the corresponding numbers in the other columns 

 as ordinates, it will be seen that the damping curves obtained with the 

 alternating magnetic fields all lie below the damping curve obtained with the 

 direct longitudinal field, which is the reverse of what we obtain in the case of 

 the soft nickel wire, as shown below. 



It was observed during the experiments with the hard nickel wire that, 

 after the alternating magnetic field had been round the wire, on attempting 

 to start up the oscillations for the next experiment by means of direct 

 ciirrents through the wire and round the solenoid, the movements of the light- 

 spot were more sluggish than formerly, or it took a longer time to get up 

 to the maximum amplitude of 300 on the scale, which seemed as if 

 the alternating magnetic field had made the wire for the time being 

 partially non-magnetic. 



This was very strongly marked when alternating magnetic fields of 

 frequencies 100 and 140 per second were round the wire. For example, 

 before subjecting the wire to tliese alternating magnetic fields, we sent an 

 equivalent direct current round the solenoid, and a certain known direct 

 current through the wire, and obtained a twist of the lower end of the wire 

 corresponding to a steady deflection of the light-spot on the scale of forty-one 

 divisions or millimetres. 



We then switched off both these direct currents, and put on the solenoid 

 an alternating magnetic field of frequency T40 per second, and of the same 



