222 



Scienf/Jic Proceedings, Royal Dublin Sociely. 



previously by one of us with a nickel wire of the same length, diameter, 

 and softness, with a load of r5 x 10* grammes per sq. cm., but in a contimiotis 

 longifuditial ma (luetic field of 'BOO c.g.s. units. 



By comparing the values in Table I with those in Tables II and III, it 

 will be seen that with the wire in the hard state (Table I), the damping 

 curves due to the alternating magnetic fields at the different frequencies all 

 lie below the curve obtained with the direct longitudinal field of equal value, 

 whereas in the case of the soft wire (Tables II and III) the curves due to 

 the alternating fields all lie above the curve obtained with the longitudinal 

 field. 



The physical state of the wii-e has a very marked effect on the rate of 

 damping of the torsional oscillations, as shown in Table TV, where, for 

 convenience of comparison, we have grouped the results for liard and soft wire 

 respectively, the load in each case being 10* grammes per sq. cm., and 

 magnetic field of 17 c.g.s. units, produced by a direct current and alternating 

 currents of frequencies 20 and 100 per second. 



Tabi,e IV. 



The examination of the figures given in Table IV shows: — 1. In a liard 

 wire the damping due to an alternating magnetic field is greater than that 

 due to an equivalent direct magnetic field ; whilst, in the case of the soft 

 wire, the damping due to the alternating field is less than that due to the 



Soieiit. Proc. Eoy. Dub. See, vol. xiii (N.S.), No. 3, p. 35. 



