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THE CHANGE OF LENGTH IN NICKEL WIEES OF DIFFERENT 

 RIGIDITIES, DUE TO ALTERNATING MAGNETIC FIELDS OF 

 FREQUENCIES UP TO 150 PER SECOND. 



By WILLIAM BROWN, B.Sc, 

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



[Read December 21, 1915. Published February 28, 1916.] 



Early in the year 1914 the present writer brought before this society the 

 results of some experiments on the change in the length of a soft nickel wire 

 when it was subjected to the influence of alternating magnetic fields of 

 frequency 50 per second. 1 



The present communication gives results obtained with nickel wires in 

 five different states of rigidity, when they were subjected to the influence of 

 longitudinal magnetic fields, direct and alternating up to a frequency of 

 150 per second. 



The rigidity of each wire was measured by means of a slightly modified 

 form of Searle's torsion apparatus already explained in a previous paper by the 

 writer.' In the case of each wire employed the length was 226 cms. and 

 the diameter - 169 cm., and the magnetic field was in every case uniform 

 throughout the entire length of the wire. The longitudinal loads used were in 

 the ratio 1, 4, 16, the greatest load being 2 x 10 5 grammes per sq. cm. 



The change in the length of the wire when the magnetic field was applied 

 was read off directly by means of a microscope reading to 9 - 2 x 10~ 7 per unit 

 length of the wire, as already explained in the author's former paper. 3 



The temperature of the room during the experiments was kept as nearly 

 as possible at 17°C. 



It was found that when a direct magnetic field was started round the 

 wire, and during the application of an alternating magnetic field, that the 

 wire became slightly heated, as shown by the slight elongation observed by 



1 Scient. Proc. Roy. Dub. Soc, vol. xiv, No. 21. 



2 Scient. Proc. Roy. Dub. Soc, vol. xii, No. 36, p. 481. 

 3 Scient. Proc. Roy. Dub. Soc, vol. xiv, No. 21, p. 298. 



SCIENT. PROC. B.D.S., VOL. XV., NO. V. <J 



