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XVII. 



MECHANICAL STRESS AND MAGNETISATION OF IRON. 

 Part II. 



By WILLIAM BROWN, B.Sc. 



[Eead Apkil 20. Ordered for Publication May II. Published June 21, 1909.] 



A PREVIOUS communication brought by me before tbis Society^ contained 

 some results obtained in investigating tlie relations between mechanical 

 stress and magnetisation with iron wires, which wires in most of the 

 experiments were not in a uniform longitudinal magnetic field tliroughout 

 tlieir entire lengths. Tlie results which I now submit were all obtained 

 with the iron wires in a perfectly uniform magnetic field. 



The arrangements for the first part of the experiments were the same as 

 those described in tlie former paper, where the wire under test was suspended 

 in a vertical direction, and joined in series with a moving-coil ballistic 

 galvanometer, having a resistance of 325 ohms. 



The galvanometer-scale was placed at a distance of lOl'S cms. from the 

 galvanometer-mirror, and was divided into 700 divisions in a length of 4i 

 cms. An earth-inductor was so arranged that it could be inserted in the 

 circuit, and the constant of the galvanometer tested at any part of the 

 experiment.^ 



In order to get the uniform longitudinal magnetic fields stronger than 

 the vertical component of the Earth's magnetism, a long solenoid was used, 

 which had 7707 turns, in four layers, and total length of 236 cms. The 

 internal magnetic field of this solenoid was perfectly uniform in strength for 

 a distance of 226 cms., or to within 5 cms. of each end. The wire under 

 test was suspended in the middle of this solenoid, in a magnetic field of 



' Scient. Proc. Roy. Dublin Soc, 1909, vol. xii., p. lOI. 

 '' Ibid., Fig. 1, p. 103. 



SCIENT. PEOO. n.D.S., VOL. XII., NO. XVII. 2g 



