524 



Scientific Proceedings, Royal Dublin Society. 



wire under test of its load, and put round the solenoid a direct current to give 

 a magnetic field of 20 c.g.s. units for a few seconds, and then a low frequency 

 alternating magnetic field for a few seconds more ; tbe wire will then be quite 

 recovered and in its original unfatigued state. The observations were taken 

 with alternating- magnetic fields of five different frequencies. The results for 

 the fatigue are given in Table II, and are shown as 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. 



Table II. 

 Rigidity == 790 y 10* grammes per sq. cm. 



From the figures in Table II, and the curves iu Fig I, it will be seen that 

 wlien the frequency of the applied alternating magnetic field is 50, the 

 maximum fatigue of the wire for that rigidity is 0-27, and it takes eight 

 minutes to attain it ; when the frequency is 100, the maximum fatigue is 0'45, 

 and takes place in six minutes, and for the frequency 150 the fatigue is 0-6, 

 and occurs in four minutes, whilst still higher frequencies fail to fatigue 

 the wire more than 0-6, though the actions take place in sliorter periods 

 of time. 



