0. Bancs- — Viscosity of Solids. 205 



configuration definitely broken up by annealing, does not re- 

 combine on cooling. In pure metal, and up to a certain limit- 

 ing (small) stress, configurations broken up by stress may re- 

 combine when stress is released or reversed. § 17. 



If degrees of temperature be replaced by arcs of permanent 

 set (mwi mut.), then these laws apply at once to motional an- 

 nealing as defined in § Sh. 



17. In certain comparisons between the strain effect exhibited 

 by glass and by steel,* we were led both by gravimetric and 

 by polariscopic observations to this distinction : the strain in 

 hard steel is very perceptibly affected by annealing tempera- 

 ture as low as 50°, whereas in the case of quenched glass (Ru- 

 pert drop), perceptible annealing is incipient only at 200°. 

 The bearing of this result on the present discussion is manifest : 

 the difference of behavior is due to the absence in glass of any- 

 thing equivalent to the unstable carbon configuration in hard 

 steel. The case of glass is nearly that of soft steel, and the 

 behavior as regards viscosity in these two instances are similar. 



Schrceder'sf important result has relevancy here : in the case 

 of hard drawn wire (Ag, Fe, german silver), minimum vis- 

 cosity is found associated with maximum susceptibility to tem- 

 perature. This is the general deduction from steel, for vary- 

 ing intensities both of temper strain and of drawn strain. § 13. 



18. Following the suggestion of §14, it may be inferred that 

 in case of very complex molecular structure, instability of con- 

 figuration will be a more probable occurrence, than in the case 

 of simple bodies, ccet. par. Complex structured matter may 



•be looked upon as a solidified mixture of homologous chemical 

 series, with a predominating member to give the substance 

 character. Conformably with this view the complex organic 

 solids:): like silk, ebonite, show more pronounced viscous defor- 

 mation than metals or mineral solids. These known facts are 

 thus in general accordance with the present theory. Nor is it 

 remarkable, that a complex substance like glass, lies some- 

 where between hard steel and soft steel, in the scale of vis- 

 cosity. 



On the other hand, when the atoms of the molecule are all 

 alike, and the structure of the substance is essentially atomic, 

 we meet conditions favorable to permanent set. This is prob- 

 ably the case with many metals. 



19. Maxwell's theory lends itself at once to the explanation 

 of superposition (perfect or imperfect) of viscous motions, 

 inasmuch as the interpretation given is independent of the 

 special peculiarity of the strain to be discussed. I will adduce 

 a few magnetic results which bear upon this point. 



*B. and S.: this Journal, xxxii, p. 185, 1886; xxxi, p. 451, 1886. 



f Schroeder: Wied. Ann., xxviii, p. 369, 1886. 



% Cf. Kohlrausch: Fogg. Ann., cxxviii, p. 414, 1866, and many others. 



