O. Barus — Viscosity of Solids. 197 



rods free from strain are compared.* The exceptions of table 

 2 are due to the fact that latent strains influence ((p — <p f ) / r to a 

 relatively much greater extent than J —J / o . Again if z/ 100 — J' 20 

 and (ip — <p')/r be compared at 100°, table 2 shows that in this 

 case also the two quantities increase and decrease together. 

 Indeed the data for 100° are the more uniform, a result due to 

 the fact that at 100° much of the latent torsion is made to 

 vanish because of the annealing effect of 100°. Data of even 

 greater uniformity cost, par. are to be looked for at higher 

 temperatures.f 



If a comparison is made between the mean rates at which 

 viscous deformation and resistance increase together with tem- 

 per, at £0° ((<p-<p f )/r and A- A' ^ and at 100° ( (<p-<p f )lr and 

 A 100 —A\ ), it is seen that the mean rate of increase of {<p—<p f ) / ' r 

 relatively to A— A' is about ten times as great at 100° as at 20°. 

 This is the phenomenon in virtue of which the viscous be- 

 havior of steel, regarded as a test of Maxwell's theory, is 

 almost crucially important. I shall endeavor to explain it. 



10. Dr. Strouhal and I defined the glass-hard state of steely 

 as the stage of temper which undergoes incipient annealing at 

 mean atmospheric temperature. Inasmuch therefore as anneal- 

 ing is demonstrably accompanied by chemical decomposition^ 

 even at temperatures slightly above mean atmospheric, the 

 molecular configuration of glass-hard steel is always in a state 

 of incipient change || A part, though not the whole, of this 

 change must be of a permanent kind ; and I wish to keep in 

 mind that at the temperature of incipient annealing the heat 

 motion is such that broken configurations are sometimes recon- 

 structed. 



Inasmuch therefore as glass-hard steel contains more unstable 

 configurations than any other state of temper, at the same tem- 

 perature, it follows from Maxwell's theory that glass hard steel, 

 despite extreme hardness, must be the least viscous member of 

 the whole group of tempered and soft steel. This strikingly 

 anomalous prediction of the theory is verified both by the re- 



* B. and S. : this Journal, (III), xxxiii, pp. 26, 27, 1887. 



f Maxwell's words are (1. c): "... but if, on account of rise of temperature 

 . T. the breaking- up of the less stable groups is facilitated, the more stable groups 

 may again assert their sway, and tend to restore the body to the shape it had be- 

 fore deformation." 



% Wied. Ann., xi, pp. 962, 963, 1880. 



§ B. and S. : This Journal, (III), p. 276, 1886. 



I During the last three years I have been making experiments on the secular 

 annealing of cold hard steel. The results are very striking and show that mean 

 atmospheric temperature acting on freshly quenched steel for a period of years, 

 produces a diminution of hardness nearly equal to that of 100° C, acting for a 

 period of hours. I examined some twenty rods, the specific resistance of which, 

 within thirty-seven months, has fallen from 465 to 42'5. in the case of thin rods 

 (diameter <^-08 cm ), and from 43-7 to 354 in the case of thicker rods (diameter 

 0-13 cm ). Freshly quenched pieces showed resistances as high as 50, nearly. 



