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XXVI. 



THE FATIGUE OF NICKEL AND lEON WIRES WHEN 

 SUBJECTED TO THE INFLUENCE OF ALTERNATING 

 MAGNETIC FIELDS OF FREQUENCY 50 PER SECOND. 



By WILLIAM BROWN, B.Sc, 

 Professor of Applied Physics, Eoyal College of Science for Ireland, Dublin. 



[Read November 24, 1914. Published January 6, 1915.] 



Section I. 



Nickel Wires. 

 In a recent communication to this Society, on the subsidence of torsional 

 oscillations in nickel wires when subjected to the influence of alternating 

 magnetic fields, it was incidentally shown that under certain conditions the 

 wire became temporarili/ fatigiied, aud a statement was then made that this 

 property of nickel wire would be further investigated.^ 



At that time, the fatigue was observed wlieu alternating magnetic fields 

 of frequencies 100 and 140 per second were used ; but since the wave- 

 forms — obtained by means of an oscillograph — of the alternating currents 

 producing these magnetic fields were found to contain the third harmonic, 

 the investigation of the effects produced by high frequency magnetic fields 

 has been held over until high frequency alternating currents of sine-wave 

 form are available. The present communication therefore gives results 

 obtained with alternating magnetic fields produced by currents of frequency 

 50 per second only, and with current wave-forms of very nearly pure sine- 

 curves. 



The results obtained and recorded below are smaller in magnitude than 

 in the two eases referred to above, as may be expected, because the frequencies 

 of the magnetic fields then employed were about two and three times the 

 frequencies used in the present ease. 



It is known^ that the continuous direct magnetic field which must be 

 round a nickel wire in order to obtain the maximum twist or " Wiedemann 

 effect " depends on the longitudinal load on the free end of the wire, for a 

 given constant current tkrougli the latter. 



In the experiments described below these conditions have been followed ; 



1 Scient. Proo. E,oy. Dub. Soc, vol. xiv, p. 219. - Jhid,, i-ol. xiii, p. 31. 



