344 Scientific Proceedings, Royal Dublin Society. 



The uiifatigued or first deflection was now 11 divisions on the scale as com- 

 pared with 7 divisions when the wire was harder, and it was found that the wire 

 in this comparatively soft state could not be fatigued at all. The alternating 

 magnetic field was put round the wire for a full hour, and the wire tested at 

 intervals, when no trace whatever of fatigue was observed. This shows the 

 narrow limits of rigidity between which the fatigue of iron wire occurs, for 

 in the wire under test a difference of about 2 per cent, in the rigidity makes 

 all the difference between fatigue and no fatigue. 



This work is being continued with alternating magnetic fields of frequencies 

 from 60 to 240 per second, and it is very probable that with these compara- 

 tively high frequencies the fatigue of both nickel and iron wires will be found 

 to take place much more rapidly than with the low frequency of 50 per second 

 employed to obtain the present results ; indeed, the two previous cases of 

 nickel wires referred to above would seem to indicate that rapid fatigue is to 

 be expected with high frequency alternating magnetic fields. 



