192 C. Bar us — Viscosity of Solids. 



different at 100°. In No. 4, the effect of -f-r following — r is 

 even more phenomenally pronounced, both at 20° and particu- 

 larly at 100°. In No. 5 the wires nearly identical at 20° show 

 differences at 100°. In No. 6 this is true in even much greater 

 degree, whereas in No. 7 wires differing considerably at 20°, 

 show relatively small differences at 100°. And so I might go 

 through the series. Nos. 13 and 14 are wires originally free 

 from strain (shear) ; but vagueness also appears in these. 



Careful inspection of the tables reveals the law, that vis- 

 cous deformation takes place at numerically greater rates dur- 

 ing the even twists than during the odd twists which immedi- 

 ately precede them respectively. Aside from these oscillations, 

 the effect of twisting here, as in § 7, is pronounced increase of 

 viscosity. 



Maxwell's theory accounts for the stated vagueness of be- 

 havior at once. In two samples of a complex substance like 

 steel, the distributions and relations of the unstable molecular 

 configurations will only in very rare instances be physically 

 and chemically identical. The foregoing paragraph shows that 

 such identity is rare even in pure homogeneous metal. § 9. 



The effect of twisting alternately in opposite directions is of 

 so great importance in its bearing on Maxwell's theory that 

 I made further special experiments. From these I select the 

 following example, tabulating it as in case of table 1. The 

 normal No. 1, An. 450° has been described. No. 18, An. 25°, 

 or glass-hard, is carefully selected free from latent torsion, 

 having experienced no other strain prior to the examination in 

 table 4, than that incident to tempering (quenching). There 

 are twelve alternations of twist, indicated by subscripts, and 

 the current time in hours and minutes of each is given. I also 

 give under m, the time in minutes which refers specially to 

 the duration of each twist. No. 1 being of greater viscosity, 

 r and {cp—cp') /t are alike in sign, by agreement. 



Experiments made by counter-twisting two glass-hard wires 

 gave results like this, but on a smaller scale. To compare the 

 results of table 4 perspicuously it is sufficient to construct the 

 differences, A ((p— <p') / r, of the respective value of {(p—<p')lT, 

 at two and four minutes after twist is imparted. These are 

 then to be compared in their dependence on current time. 

 Phenomena of this kind were called " accommodation " by 

 Streintz,"* their discoverer, by Wiedemann, f Kohlrausch,^ and 

 others. The fact that Boltzmann's law contains them is among 

 its chief excellencies. 



* Streintz: Pogg. Ann., cliii, p. 406, 1874. 



f Wiedemann: Wied. Ann., vi, p. 512, 1879. This work is the most searching 

 and comprehensive of the relevaut researches. 



\ Kohlrausch: Pogg. Ann., clviii, p. 371, 1876. Cf. Schmidt: Wied. Ann., ii r 

 p. 48, 1877. 



