Strains Mechanically Applied. 177 



wire, increase viscosity (motional annealing). If this treat- 

 ment is intensified beyond a critical stage, in other words 

 if stress is increased sufficiently beyond the limits of resi- 

 lience and toward the limits of rupture, then viscosity is again 

 seriously decreased. For the action of stress has now become 

 such as to introduce its own specific instability, whereby 

 viscous deformation is again promoted, 



14. Having thus substantiated the remarks of § 10, and 

 shown that the accordant results of the earlier observers and 

 my own are such as follow naturally from MaxwelFs theory, 

 it is expedient to give a graphic representation of the more 

 important differential data (^. e. differences between strained 

 and soft metal for each case of stress) in hand. In figure 2, 

 the viscous deformation (<f> — (f>')/T, produced by the action of 

 a fixed rate of twist t, is represented as ordinate, time as 

 abscissa. The material is steel, the originally soft state of 

 which has been transformed by temper (glass-hardness), 

 drawn strain (wire-plate), tensile strain, and torsion respec- 

 tively. Curves are given for intense values and for moderate 

 values of stress. The nature of the problem precludes greater 

 definiteness as to stress data. In case of traction infinitesi- 

 mally below the point of rupture, for instance, viscous de- 

 formation would occur with such extreme rapidity that its 

 diagrammatic representation would be a vertical line. 



Again, in case of traction of sufficiently small value, the 

 curve would be a horizontal line coinciding with " soft," or 

 even a curve below it (motional annealing). In a measure 

 this is true of the other strains ; and I have therefore ex- 

 pediently inserted the values for deformations actually found. 



The general outcome of the present paper is this, that the 

 eff'ect of strain of whatever kind, applied in sufficient intensity 

 to homogeneous soft steel, is marked diminution of viscosity. 

 Again, inasmuch as the underlying cause of viscous deforma- 

 tion is the occurrence of unstable configurations the number 

 of which is being reduced in the course of viscous motion, 

 Maxwell's theory naturally suggests the applicability of ex- 

 ponential equations for the description of the time relations 

 of such motion. From another point of view it appears that 

 the loss of viscosity experienced by a given metal, under 

 action of a given kind of strain, may not inappropriately be 

 used as a measure of its intensity. Finally, the curious 

 observation, that in all the cases given loss of viscosity has 

 taken place simultaneously with increase of hardness, is one 

 of the suggestive results of the experiments made. 



Phys. Lab., U.S.G.S., 



Washington, D.C., U.S.A. 



Phil. Mag. S. 5. Vol. 27. No. 165. Feb. 1889. N 



