312 



Scientific Proceedings, Royal Dublin Society. 



Tlie same methods of experiment and observation were carried out with the 

 iron wires as was done in the case of the nickel wire explained above in Section 1. 

 The wire used was at first in the physical state in which it was received from 

 the manufacturer, that is, its simple rigidity was about 810 x 10^ grammes 

 per sq. centimetre. The effective jeiigth of the wire was 226 cms., and the 

 diameter 0'162 cms., tlie load used being 10* grammes per sq. centimetre, and 

 tlie magnetic field round the wire in order to get the maximum effect was 

 2"8 e.g.s. units. 



The results obtained with this hard wire are given in Table V, and are 

 shown in a curve in fig. 2, where also for comparison is placed a correspond- 

 ing curve for nickel wire. 



Table V. 



From these curves it will be seen that the maximum fatigue for the iron 

 wire is about 0'3, and that it took thirty minutes' application of an alternating 

 magnetic field of 2"8 units to give this amount ; and also that it takes about 

 three times longer to fatigue an iron wire than it does to fatigue a nickel 

 wire when they are of the same length and diameter, and when subjected to 

 the same longitudinal load. 



The nickel wire liad a simple rigidity of about 790 x 10^ grammes per sq. 

 centimetre and the iron wire 810 x 10* grammes per sq. centimetre, that is 

 botli wires were as hard as they could be without the " Wiedemann effect" 

 being'entirely annulled. 



The iron wire was now taken out of the solenoid and hung vertically under 

 its own weight only, and by means of a broad Bunsen flame it was heated 

 ticice to a dull red heat from the top downwards in order to allow it to cool 

 slowly. When cold, the rigidity was again measured, and found to be about 

 7i>'5 X 10* grammes per sq. centimetre ; it was then placed in the solenoid and 

 tested in the same way as formerly. 



