BuowN — Mechanical Stress and Magnetisation of Iron. 499 



temper Ho, 32 per cent, in the wire Hi, and 38 per cent, in the wire Hj, 

 i.e., increased load has more effect on a hard wire than on a soft one. 



When the curves relating to load and twist in the three tempered wires 

 Hj to H, were produced, they all cut tlie axis of abscissse at points 

 approximately equivalent to the elastic limit of tlie wire. 



The twist diminishes as the simple rigidity increases, and also as the 

 load increases. When the hardness is increased from Ho to Hj, the twist is 

 decreased 16, 22, and 29 per cent, respectively, when tlie loads on the wires 

 were O'o, 1-5, and 3*0 x 10^ grammes per sq. em. 



When the wire becomes harder — between certain limits Hq to H2 — 

 as the length of the wire is decreased, and the load on it increased, the 

 twists gradually approach the same value as the surrounding longitudinal 

 magnetic field is increased. 



In wires of different degrees of magnetic softness, the longitudinal 

 magnetic field in whicli tlie maximum twist occurs is independent of tlie load 

 on the end of the wire between certain limits. 



With iron wires in the same physical state but of different diameters, the 

 maximum twist occurs in longitudinal magnetic fields of different strengths — 

 the thicker the wire the higher is the magnetic field in which the maximum 

 twist occurs. In a magnetic field of three imits the twist is doubled when 

 the cross-sectional area of tlie wire is increased nine times. 



The magnitude of the longitudinal magnetic field in which the maximum 

 twist occurs is directly proportional to the current density in the wire. 



With a given load on the wire, and a given current through it, the twist 

 in a given longitudinal magnetic field is inversely proportional tothe cross- 

 sectional area of the wire, or directly proportional to the current density 

 in it. 



SCIENT. PKOC. K.D.S., VOL. XII., NO. XXXVI. i B 



