C. Bar us — Viscosity of Solids. 191 



When two wires as nearly as possible identical (chemically 

 and physically) are compared, the question arises in how far 

 viscosity may vary with the time elapsed after annealing. 

 The experiments made showed slight increase with the time 

 given to the molecules to subside after annealing in air. The 

 magnitude of these results is insignificant and often obscure 

 and by no means comparable with the data of table 3. It 

 follows that these are not a direct heat effect. Again the sign 

 of the twist r, in table 3, is the same throughout. It must 

 therefore be asked whether in these experiments an earlier 

 stage of viscous subsidence overtakes a later stage. To throw 

 light upon this point, it is sufficient to reverse the sign of the 

 twist alternately, without fresh annealing ; or to reverse the 

 sign of the twist with each alternate annealing of the upper 

 and lower platinum wire. In such a case a latent strain, fav- 

 orable to motion, is imparted to the wire not annealed. Ex- 

 periments which I made in some number show that the results 

 of table 3 hold good, the character of the motion being dimin- 

 ished in degree, but not in sign. 



All these results follow at once from Maxwell's theory. 

 They show that the above viscous effect of twisting is to be 

 referred to motion of molecules which accompanies it ; mole- 

 cules are placed in new relations relative to each other ; un- 

 stable configurations are thus continually broken up, the action 

 beginning at the outside layers. By reversing the sign of the 

 twist, the original configurations are only partially restored, at 

 best, even for small permanent set, such as is here in question. 

 Finally the effect of prolonged and repeated twisting is stiff- 

 ness, because all the unstable configurations have collapsed, and 

 the intrinsic molecular energy is the potential minimum com- 

 patible with the given conditions. 



8a. Steel wires were used in our earlier work,f free from 

 torsion strain. The hard steel wires of the present paper, 

 employed in other researches, may contain twists stored up 

 like residual magnetism. This produces a kind of unilateral 

 symmetry, so far as torsions are concerned ; but it is not other- 

 wise objectionable. In critical cases wires free from latent 

 torsion are selected. 



Turning to table 1, the individual wires are found to show 

 wide differences of viscous behavior : In No. 2, the viscous 

 subsidence takes place at nearly the same rate for — r and for 

 + r, both at (9-20° and at 0=100°. In No. 3 the effect of-r 

 and +r is of different magnitude at 20°, and enormously more 



* The thermal effect without annealing is so nearly negligible as to prove that 

 in Dr. Schroeder's work (Wied. Ann., xxviii, p. 369, §§ 8, 13, 17. 1886), the ob- 

 served result is to be ascribed to annealing hard drawn wire. 



f B. and S. : this Journal, III, xxxii, p. 448, 1886; xxxiv, p. 4, 1887. 



