﻿52 Dr. W. Peddie on 



and a condition of zero resilience indicated by 



*4 • • • w 



the relation between and Q being 



o =0(n + lf (8) 



As the torsion of a wire is increased, the set and the differ- 

 ence between the angle of torsion and the angle of set 

 increase. This goes on until the angle is reached. As the 

 twisting couple is further increased, the set increases at a 

 greater rate than the torsion. The stronger configurations 

 now break down, and the removal of the twisting couple is 

 followed by small recoil. If the twisting couple be maintained 

 in excess of the value required to overcome the maximum 

 resilient couple, work is done constantly in breaking up 

 molecular groups, and the material of the wire flows steadily, 

 the angle of torsion and the set increasing at constant equal 

 rates. Under that constant couple there is also constant 

 resilience. The condition corresponding to the theoretical 

 angle O is attainable under a finite couple of moment 

 k'0 n + J = Jc0 o . Thus the theory indicates that the melting-point 

 is conditioned by shearing-stress. 



The flow will of course commence at the surface of the 

 wire. The angle might also be called the Angle of Plas- 

 ticity, and the couple k0 o might be termed the Couple of 

 Fluidity. 



Relation between Torsion and Set. 



If we assume that the torsional rigidity is not sensibly 

 altered by set, the quantity k is constant, and we may write 

 (3) in the form 



where a is the angle of set. This gives 



-•('Vi-L-9- 



To test this expression I have used Wiedemann's statical 

 observations given in Table I. p. 4, Phil. Mag. 1880, vol. ix. 

 I find that the equation 



a = 0(1 — ^l-896(10)- l6 (9 3 ' 548 ) 

 corresponds to a remarkable extent with his observations. 

 The curve in fig. 2 represents this equation with values of 

 as ordinates and values of a as abscissae ; and the points on 

 or near it represent Wiedemann's results. No stronoer 

 confirmation of the theory need be desired. 



