Bkown — Mechanical Stress and 3!lagneiisation of Iron. 491 



meet the axis of abscissae at a meau point eorrespondiug to a load on the 

 wire of about 8x 10* grammes per sq. cm. 



It is interesting to notice, for the above three states of hardness 

 H„, Hi, aud Hi,, that as the length of the wire is diminished and the 

 load on the wire increased, the twists gradually approach to the same 

 value as the longitudinal magnetic field round the wire is increased. 



Two new wires were now taken and prepared to give the degrees of 

 hardness H^.t aud H3 ; these were tested when at the full leugtli of 226 em. 

 only for three loads and for twehe different magnetic fields. 



The rigidity of H.;, was 812 X 10* grammes per sq. cm., its electrical 

 conductivity 12-5, and its cross-sectional area 20'46x 10"^ sq. cm. 



The wire H^ had a rigidity of 823 X 1 0* grammes per sq. cm., electrical 

 conductivity 9'1, and cross-sectional area 20-35 X 10"^ sq. cm. The results 

 of the tests are shown together in Table VI. 



As will be seen from fig. 1, page 482, these two wires liave departed 

 from the straight-line relation between the rigidity and the load on the end 

 of the wire when heated, exhibited by- the first three, that is, they have 

 become more rigid or harder in proportion ; the electric conductivities 

 have also diminished at a more rapid rate. 



When, however, the loads are plotted against either the maximum 

 twist in a field of 2-5 units, or the areas of the cyclic curves, they still 

 show the straight-line relation found with the previous three tempered wires. 



In all the experiments on these wires in different states of magnetic 

 softness, tlie maximum twist takes place in a longitudinal magnetic field of 

 about 2-5 c.g.s. units. In the paper by Nagaoka and Houda,^ already 



Phil, Mag., 1902, 6th Ser., vol. iv., p. 61. 



