178 



Scientific Proceedings, Eojjal Dublin Societij. 

 Table I. 



If the numbers in the first column of this table be plotted as abscissae and 

 those in the second column as ordinates, it will be found that the points all 

 lie very approximately in a straight line ; and it will also be seen that the 

 area of tlie cyclic curve or circular magnetism is decreased about 20 per cent, 

 when the longitudinal stress or load on the wire is inci'eased about seven 

 times, i.e. when the wire is in a magnetic field of 2'5 units. In the former 

 paper it was shown that when the same size of wire was placed in the Earth's 

 vertical field of 0'45 units, and when tlie longitudinal stress per unit area 

 was increased 3'5 times, the circular magnetisation was decreased 40 per cent. 

 This is what one would expect, for on the curve of magnetic field and twist 

 in fig. 8 of the previous paper' the lower field is on a part of the curve where 

 the slope is rapidly changing, and the higher field is on the peak of the 

 curve, so that any changes in tiie load and circular maguetism would be more 

 pronounced in the weak field. 



Wlien the values in the third column of Table I. are plotted as ordinates 

 against the load as abscissae, the points will also be found to lie in a straight 

 line practically parallel with the other line, and for the same increase of the 

 longitudinal stress on the wire, viz. about seven times, the maximum transitory 

 current is diminished about 23 per cent. 



In order to test the effects of various longitudinal magnetic fields on the 

 different wires when each was under a constant longitudinal stress or load of 

 10' grammes per sq. cm., the five wires, Nos. 12, 14, 16, 18, and 20, were all 

 carefully annealed and successively tested when placed in magnetic fields 

 ranging in value from 0'45 to 14 c.g.s. units. The complete areas of the 

 cyclic curves or the circular magnetism were measured, and the maximum 

 transitory current observed in each case ; the results obtained are here given 

 in Table II., and sliown in curves in fig. 2 and fig. 3. 



' Sclent. Proc. Hoy. Dublin Soc, 1909, vol. xii., p. 118. 



