[ 12.1 ] 



XII. 



THE CHANGE OE LENGTH IN NICKEL WIRES DUE TO 

 TRANSVERSE MAGNETIC FIELDS DIRECT AND 

 ALTERNATING. 



By WILLIAM BROWN, B.Sc, 

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



Read March 28. Published May 26, 1916. 



A considerable amount of work has been done on the change in the length 

 of iron and nickel wires and rods when they were subjected to the influence 

 of magnetic fields, and an excellent list of papers on the subject, ranging from 

 1847 to 1908, is given by Dorsey. 1 Subsequent investigations, bringing the 

 work up to 1916, have been made by Williams, 2 Heaps, 3 and the present 

 writer, 1 the latter working with alternating as well as direct longitudinal 

 magnetic fields. 



Several workers have tried the effect of transverse magnetic fields on iron, 

 but, with the exception of Williams in 1914, and of Heaps in 1915, whose 

 results were more of a qualitative than quantitative nature, no one — as far 

 as the present writer knows — has obtained definite quantitative results on 

 the effect of direct and alternating transverse magnetic fields on nickel. 



The present communication gives some results obtained with soft nickel 

 wire when it was subjected to the influence of transverse magnetic fields, 

 both direct and alternating. The transverse magnetic fields employed in 

 the experiments were produced in a gap of a soft iron tube by means of five 

 insulated copper wires inside the tube, the return wires of the circuit being 

 200 cms. distant. The iron tube had a slot cut right through the wall along 

 its whole length of 215 cms., the other dimensions of the tube being 2 - 54 cms. 

 external diameter, L6 cm. internal diameter, breadth of face of slot - 47 cm., 

 and width of slot - 8 cm. The copper wires in the tube were each 0'4 cm. 

 diameter, and were each insulated by being painted with two coatings of 

 anti-sulphuric enamel, then with one layer of silk ribbon ; and when they 



1 Phys. Rev., vol. xxx, p. 718. 



2 Phys. Rev., vol. iv, p. 498, 2nd Series. 



3 Phys. Rev., vol. vi, p. 34, 2nd Series. 



4 Scient. Proo. Roy. Dub. Soc, vol. xiv, p. 297, and vol. xv, p. 41. 



SCIENT. PEOC. E.D.S., VOL. XV., NO. XII. U 



