Bkown — Meclumical Stress and Magnetisation of Iron. 119 



shown to be obtained in a field of about 10 c. g. s. units, which depends, 

 however, on the value of the current in the wire. 



From the two lower curves in fig. 8 we see that as the field is increased 

 from 4 to 13'5 units, or about three times, the circular magnetism or area of u 

 cyclic curve is decreased about 50 jDer cent, for the smaller load, and 60 per 

 cent, for a load 2'43 times greater. From some experiments which are now 

 in progress, but just started, with the wire in a uniform magnetic field 

 throughout its entire length, it has been found that the maximum transitory- 

 current produced by twisting through 100° a wire of the same dimensions, 

 and with the same load on, as the one used above, was obtained in a field 

 of 2-5 c. g. s. units; so that for fields from 0-45 to 4 units the first part 

 of the curve, fig. 8, would probably be as shown by the dotted lines.^ 



The whole six wires were re-annealed by means of the bunsen flame, 

 and the maximum twist or deflection on the scale measured. In each case 

 the longitudinal stress or load was IC^ grammes per sq. cm., and the current 

 density through each wire 100 amperes per sq. cm. as before. The tests 

 were made when the wires were in the Earth's vertical magnetic field, and 

 also when they were inside the solenoid with a total magnetic field of 

 7 0. g. s. units. The results are here given in Table VIII., and shown in 

 curves in fig. 9, where the cross-sectional areas of the wires in sq. cms. are 

 abscissse, and the twist or maximum deflections on the scale are ordinates- 



TABLE VIII. 



1 Subsequent work has shown that this is so : see figs. 2 and 3 in Part II. of this paper, which 

 was read before the Royal Dublin Society on April 20th, 1909. 



x2 



