Brown — The Change of Length in Nickel Wires. 



123 



A.C. alternating fields of frequency 50 per second. The values in columns 

 marked L are for longitudinal magnetic fields, and are taken from Table V, 

 p. 45, of a previous paper by the author. 1 The values in columns marked T 

 were obtained with transverse magnetic fields direct and alternating, the 

 latter of frequency 50 per second. 



The previous tests with longitudinal fields direct and alternating, and the 

 present tests with transverse fields direct and alternating, were performed on 

 the same nickel wire when it had on the same longitudinal load of 2 x 10 5 

 grammes per sq. cm. 



Eigidity == 708 x 10 6 grammes per sq. cm. 



Load = 2 x 10 5 „ „ „ „ 



The action of the two direct magnetic fields longitudinal and transverse on 

 nickel wire is better seen from the curves in the Figure (p. 124), where the 

 strengths of the fields are plotted as abscissas, and as ordinates the correspond- 

 ing values of the expansions, above the axis of abscissas ; and the values of the 

 contraction, beloiv the axis. 



The upper curve, or curve of expansion, when produced comes gradually 

 towards the axis of abscissee, and appears to touch the axis somewhere in the 

 region of magnetic field 1000 units ; at least, when a magnetic field of 1000 

 units was put on and off the apparatus employed, there was no change in the 



1 Scient. Proc. Roy. Dub. Soc, vol. xv. Feb. 1916. 



