490 



Scientific Proceedings^ Royal Diihlin Society. 



that when the load is increased six times, the mean maximum twist is decreased 

 about 32 per cent. These tliree straight lines when produced cut the axis of 

 abscissae at a point representing a mean load of 8'25xl0^ grammes per 

 sq. cm., wliich is about the same value as that found for the softer wire. 



Another wire was now taken and treated in the same way as in tlie 

 previous cases, but with a load on the end of 2x 10* grammes per sq. cm., 

 and was made into the state of hardness called H^. The wire was prepared 

 in the usual way, the rigidity measured and found to be 808 X 10'^ grammes 

 per sq. cm., and tlie electrical conductivity 13'6 compared with pure copper. 

 The cross-sectional area of the wire was 20-64x10"^ sq. cm., and it was 

 tested in precisely the same manner as tlie previous wires, and the results 

 are shown in Table V. 



TABLE V. 



These results, when plotted, show the same aspect of curves as was found 

 for the soft iron wires, and show that when the lengtli of the wire is halved, 

 both the circular magnetism or areas of the cycle-curve when the wire is in 

 a longitudinal magnetic field of 2'5 units, and the maximum twist, are 

 decreased about 50 per cent. 



Also, for three different lengths by plotting the load as abscissse, and 

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

 that when the load is increased six times, the mean maximum twist is decreased 

 about 38 per cent. ; and when these three straight lines are produced, they 



