2 Scientific Proceedings, Royal Dublin Society. 



As in the ease of similar experiments with nickel wires, 1 the iron wires 

 were subjected in every case — unless otherwise stated — to the same longitu- 

 dinal load, viz., 1-5 x 10 5 grammes per sq. centimetre, which corresponds to 

 the middle value of the loads employed in previous work on iron wires. 



It has been shown, for the case of iron wires, that the magnetic field 

 which must be round the wire in order to get the maximum effects for 

 torsion, fatigue, and subsidence of torsional oscillations is independent of the 

 longitudinal load on the end of the wire. 2 This is not so in the case of nickel 

 wires where the magnetic field changes with the load, so that in all the pre- 

 sent experiments the one magnetic field, 2 - 8 c.g.s. units, which gives these 

 maximum effects was used. 



The iron wires employed were each 226 cms. long, and 0-163 cm. in 

 diameter ; and the millimetre scale for reading off the amplitude of oscillation 

 in the subsidence experiments, or the steady deflection in the fatigue 

 experiments, was placed at a distance of 167 cms. from the plane mirror 

 on the vibrator or load on the end of the wire. The maximum deflection of 

 the light-spot which was used in the subsidence experiments was at the 

 distance marked 300 on the scale, which corresponded to a torsion or twist of 

 the lower end of the wire equal to an angle of about 5° 10' on each side 

 of the zero. 



In the course of the experiments on " fatigue," the direct current through 

 the wire was in each case equal to one ampere. 



The wire first tested was in the physical condition in which it was 

 received from the manufacturer, and when measured it was found to have a 

 simple rigidity of about 815 x 10 G grammes per sq. centimetre. It was 

 placed in the solenoid with the longitudinal load on the lower end equal 

 to 1*5 x 10 5 grammes per sq. cm., and was tested (1) for fatigue, (2) for 

 subsidence of torsional oscillation when subjected in both cases to continuous 

 (D. C.) and alternating (A. C.) magnetic fields of value 2 - 8 c.g.s. units. 



The results obtained for the fatigue with the different values of the 

 frequency are shown in Table I, and two of the sets of observations are 

 shown in the form of curves in fig. 1. In the table, d means the steady 

 deflection of the light-spot on the scale, and F the fatigue, and the frequency 

 of the magnetic field is indicated by n = 50, &c. 



1 Scient. Proc. Roy. Dub. Soc, 1915, vol. xiv, No. 39, p. 521. 



2 Ibid., 1910, vol. xii, No. 36, p. 484. 



