124 



Scientific Proceedings, Royal Dublin Society. 



length visible in the microscope. The maximum expansion, it will be seen, 

 takes place in a field of about 50 units, that is, in a field of about double the 

 value of the longitudinal magnetic field which gives the maximum twist 

 (Weidemann effect) with the same load on the wire, 1 this twist depending on 

 the load but independent of the current density in the wire. 2 



X 



> C 



g ft) 



.5 





X 



=81- 



«o c 

 c o 



is 



In conclusion it may be said that : — 



1. For both direct and alternating transverse magnetic fields a nickel wire 

 expands to a maximum, and then diminishes gradually for high fields. 



2. The maximum expansion for both direct and alternating transverse 

 fields takes place in the same field-strength of about 50 units. 



I am again indebted to the College Electrician, Mr. E. Macaulay, for 

 assistance in this work. 



1 Scient. Proc. Roy. Dub. Soc, vol. xiii, p. 31. April, 1911. 



2 Scient. Proc. Roy. Dub. Soc, vol. xii, p. 511. December, 1910. 



