Bkown — Mechanical Stress and Magnetisation of Iron. 489 



was thereupon taken and placed in various longitudinal magnetic fields 

 inside tlie solenoid, and there was no twist whatever of the free end of the 

 wire when a large or small current was sent through it. 



Another wire was now taken and prepared to give the degree of hardness 

 Hi, as already described above ; the rigidity was measured and found to 

 be 788x10" grammes per sq. cm., and the electrical conductivity 14'0 as 

 compai-ed with pure copper. The cross-sectional area of the wire was 

 20'73xl0"' sq. cm., and it was tested in precisely the same manner as 

 was done with the soft iron wire of liardness H^, — that is, for twelve different 

 strengths of longitudinal magnetic fields, for three different lengths, and for 

 three different longitudinal loads. 



The results are here shown in Table IV. 



TABLE IV. 



As before, if for the three different loads we plot as abseissse the lengths 

 of the wires, and as ordinates (1) the maximum twist, and (2) the areas 

 of the cyclic-curves when the longitudinal magnetic field round the wire is 

 2-5 units, the three straight lines in both cases (1) and (2) when produced 

 all meet at the origin. This shows that when the length of the wire is 

 halved, both the maximum twist and circular magnetism or area of the cycle- 

 curves are decreased about 50 per cent. Also, if for the three different 

 lengths of wire we plot tlie values of the loads on the wires as abscissae, and 

 the corresponding values of the maximum twist as ordinates, it will be found 



3z 2 



