[ 480 ] 



XXXVI. 



MECHANICAL STRESS AND MAG-NETISATION OF IRON : 



Part III. 



BY WILLIAM BROWN, B.Sc, 



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



[Read May 24. Ordered for Publication June 14. Published September 2, 1910.] 



A CONSIDERABLE amount of work has been done on various effects of 

 mechanical stress on the magnetisation of metals, and the report on the 

 subject by H. Nagaoka' tabulates all the data known up to 1899. 

 Amongst the subsequent work the following bear on the subject of the 

 present paper : — Nagaoka and Honda''' have shown that when a wire of nickel- 

 iron alloy containing nickel up to 45 per cent, is subjected to simultaneous 

 longitudinal and circular magnetic fields, the direction of twist of the free 

 end is the same as that of an iron wire. Shimizu and Tanakadate' have 

 studied the Wiedemann effect at high temperatures, and have shown that 

 for iron, nickel, and tungsten steels, it vanishes at the critical temperatures 

 of the metals. 



In the first and second parts of this paper the writer has published^ the 

 results of some experiments obtained with soft iron wires, in which the 

 longitudinal magnetism, the circular magnetism, the longitudinal load, and 

 tlie cross-sectional area of the wires were varied. The present results were 

 obtained with iron wires of different tempers, or different degrees of 

 magnetic softness, different lengths, and different diameters. 



Five different degrees of hardness were adopted, which were obtained by 

 heating the wires to a cherry-red heat by means of a broad Bunsen burner, 

 when they were hung vertically, and subjected to different longitudinal 

 loads. In the experiments for testing the effect of temper on the torsion and 

 magnetism. No. 16 size wires of the best Swedish charcoal-iron were 

 employed, this size of wire being easier to manipulate than larger or smaller 

 wires. In order, in the first place, to get the wire as soft as possible, it was 

 suspended from the ceiling of a darkened room by means of a three-jaw self- 



' Rapports du Cungres International de Physique, Paris, 1900, vol. ii., pp. 536-556. 



= Compt. Rend., 1902, torn, cxxxiv. ; and Phil. Mag., 1902, 6th Ser., vol. iv. 



3 Proc. Phys. Math. Society, Tokyo, Oct., 1906. 



* Sclent. Proc. Eoy. Dub. Soc, 1909, vol. xii., pp. 101 and 175. 



