170 Scientific Proceedings, Royal Dublin Society. 



a series of observations somewhat the same as was the nickel wire, but 

 in magnetic fields of 2'5 units. The following sets of experiments were 

 taken : — 



A. When the wire was in a direct longitudinal field. 



B. When the wire was in an alternating longitudinal field. 



C. When one ampere (direct) was through the wire and a direct longitudinal 



field round it. 



D. When one ampere (direct) was through the wire and an alternating 



longitudinal field round it. 



E. When one ampere (alternating) was through the wire and an alternating 



longitudinal field round it. 



Comparing results obtained under conditions : — 

 A and C, in C the damping is increased 2*5 per cent. 

 B and E, in E the damping is decreased 2'2 per cent. 

 B and D, there is no change. 



Appendix II. 



In this and previous papers on the fatigue of nickel and iron wires due 

 to the application of alternating magnetic fields longitudinal and transverse, 

 the fatigue has been defined and measured by reference to the " Wiedemann 

 twist." It occurred to the present writer to try if any change in the 

 resistance of nickel wire could be observed when the wire was fatigued. 

 A No. 20 s.w.g. nickel wire, 226 cms. long and of rigidity about 790 x 10 6 

 grammes per sq. cm. was wound longitudinally on a slotted wooden shuttle, 

 15 cms. long and 1"3 cms. diameter, and placed in a solenoid 30 cms. long, 

 which afforded the means of applying a longitudinal alternating magnetic 

 field to the wire. The wire thus wound was made one of the arms of a wheat- 

 stone bridge arrangement which was capable of measuring a change in the 

 resistance of approximately 1 in 5,000, and of detecting a change of approxi- 

 mately 1 in 10,000. 



The nickel wire (while in position in the bridge) was subjected for three 

 hours to the influence of a longitudinal alternating magnetic field of strength 

 30 units and frequency 50 per second. The resistance was noticed after an 

 interval of an hour to allow the temperature to come to its original value, 

 and no change could be observed within the above limits. Previous work 

 has shown that the nickel wire did not recover from fatigue within such a 

 small interval as an hour, and it may be stated that the wire which was 

 under slight tension on the wooden shuttle was not disturbed during the 

 above tests. 



It would seem, therefore, that what we call the fatigue and which can be 

 measured by the magnetic twisting of the wire is not accompanied by any 

 effect on the resistance, at least within the limits mentioned above. 



