186 



Scientific Proceedings, Royal Dublin Society. 



uaits io each experiment. The total area in sq. cms. of each of the cyclic 

 curves was then measured, and the maximum twist also observed in each 

 case ; the results so obtained are given in Table IV. 



Table IV. 



If the numbers in the first column of Table IV. be plotted as abscissae, 

 and tliose in the second column as ordinates, the points will all be found to 

 lie practically in a straight line, and will show that when tlie longitudinal 

 stress is increased about seven times, tlie area of the cyclic curve or circular 

 magnetisation is decreased about 30 per cent. If the numbers in the third 

 column of tlie table be plotted as ordinates against the same values as before 

 on the axis of abscissse, the points of maximum twist will also be found 

 to lie in a straight line, and will show tliat for the same increase in the 

 longitudinal stress (about seven times) the maximum twist is decreased about 

 14 per cent. These values were obtained in a magnetic field of 2"5 c.g.s. 

 units, or at the peak of the curve, and are therefore less pronounced than if 

 they had been taken in a magnetic field of higher or lower value. ^ 



' This same No. 16 wire when re-annealed was subsequently tested magnetometrically for the 

 B-H cyclic curves, when the wire was subjected to two different constant longitudinal loads. The 

 maximum magnetic force appUed was 24-6 c.g.s. units, obtained with the long solenoid, which 

 allowed the wu'e under test to be 1400 diameters long. The effect of the heavier load was to 

 harden temporarily the wire under test, as is shown by the following results : — 



Load in grammes 

 per sq. cm. 



Maximum 

 Induction. 



Eetentivitv. 



Coercive force. 



Loss in ergs per 

 cycle per c.c. 



0--34 X 10* 

 2-72 X 10= 



15060 

 16810 



10700 

 13300 



2-0 

 2-5 



12120 

 136S0 



These results show that, wlien the longitudinal stress jier unit area on the wire is increased 

 eight times, the maximum induction is increased about 11 "6 per cent. ; the retentivity and coercive 

 force are each increased 25 per cent., and the loss in ergs about 13 per cent. 



