166 Mr. C. Barus on the Viscous Effect of 



only by the given degrees of resilience or of brittleness. 

 Nevertheless, if the wire admits of permanent set, the analogy 

 pursued may even be pushed to this extreme detail. For, 

 just as in the case of thermal annealing above 350°, no 

 further marked effects are produced, because the intensity of 

 stored stress is invariably below the value of viscosity ; so in 

 case of motional annealing, when stress surpasses the limits 

 of resilience, further increment of marked consequence is no 

 longer elastically retained. 



II. Tensile, drawn, and other Strains in their Bearing on 

 Maxwell's Theory/ of Viscosity. 



10. It is known that the effect of drawing metallic wires 

 through a draw-plate is a marked decrease of the viscosity of 

 the originally soft metal. The diminution increases with the 

 intensity of strain imparted. It is not so well known that 

 the viscous effect of a tensile strain applied in any degree to 

 the same originally soft metal is after straining almost nil in 

 comparison. Kohlrausch* and his pupils, Streintz f and 

 others, more recently and in extensive researches Mr, Herbert 

 Tomlinson |, have occupied themselves with these phenomena. 

 The results of these observers are in general accord, and 

 agree well enough with my work that special publication of 

 new data might appear superfluous. Nevertheless, as steel has 

 been but sparingly dealt with, and as results fitting at once 

 into my diagrams are essential to my purpose, I have found 

 it desirable to communicate them. Apart from these con- 

 siderations the observations which I need must be made with 

 minute reference to Maxwell's theory. In this respect the 

 earlier work is seriously lacking. 



The striking difference in the permanent viscous eflPect 

 produced by the action of the two strains is particularly sur- 

 prising, because the strains are imparted by mechanical pro- 

 cesses not altogether dissimilar. The action of wire-pulling, 

 however, accompanied as it is by surface compression as well 

 as longitudinal extension is conducive to the permanent re- 

 tention of high-strain intensities, because it imparts to the 



* Kohlrausch's original and fundamental researches are given in my 

 earlier papers. Here I need refer only to Scliroeder, Wied, Ann. xxyiii. 

 p. 354, 1886. 



t Streintz, Pogg. Ann. cliii. pp. 895, 396, 411, 1874. 



I 11. TomJinson, Phil. Trans. 1886, ii. pp. 801 to 837. The variety of 

 strains and metals examined in this paper give it unique value as regards 

 the subject of the present section. 



