C. Barus — Viscosity of Solids. 203 



in the marked secular annealing of glass-hard steel. It is not 

 necessary for the manifestation of viscosity that the integrity 

 of the molecule be actually invaded ; but as the action intensi- 

 fies one may pass continuously from Maxwell's (§ 8b) into 

 Clausius's (§ 15) hypothesis, without being able to define the 

 line of transition, at least from the character of the viscous 

 phenomena. Cf. this Journal, xxxiv, p. 1, 188T. 



15. The observations made in the above paragraphs relative 

 to the visible viscous subsidence of a mechanical strain imposed 

 on a steel rod, apply for the complete explanation of the phe- 

 nomenon of temper. "With this purpose in view, it is merely 

 necessary to conceive of hardening or quenching (sudden cool- 

 ing of steel) as an operation by which a strain of dilatation is 

 imparted to steel. This strain, once applied, is locked up in 

 the metal in virtue of viscosity." The strained structure of 

 hard steel is proved by the fact that massive pieces of hard 

 steel often explode spontaneouslvf and by the tendency to 

 rupture during quenching exhibited by the metal. The tem- 

 per strain may be studied optically and in other ways, in glass, 

 and at low temperatures, even in resin. J 



Reckoned from the observed volume increase§ due to quench- 

 ing, the stress-intensity corresponding to the observed strain 

 may be estimated at 10 10 degrees per square cm. in steel, and 

 10 9 degrees per square cm. in glass. It is thus of the order 

 of the respective tenacities of steel and of glass. 



In view of the fact that the viscosity of glass hard steel is 

 not above that of glass. |; exceptionally great strain intensity 

 though impartable, would not be permanently retained. Hence 

 the secular changes of glass-hard steel. Cf. § 10. footnote. At 

 this point the function of carbon appears. Sudden cooling 

 induces carbon and iron to remain in the combined state in a 

 way favorable to the dilatation in question. Throughout the 

 process of cooling carbon and iron at any place within the 

 metal are united in conformity with the given degree of car- 

 buration and with the strain there experienced. In the cold 

 metal, at the given place, strain is to a certain extent perma- 

 nent and independent of the surrounding medium of steel. •[ 

 Hence if by gradual secular annealing of massive glass hard 

 steel, a sufficient number of carbon configurations are broken, 



*Cf. Bull. U. S. G-. S., No. 14, p. 88 ; 1885. 



f Batchelder: Journ. Franklin Inst. (3). viii. p. 133. 1844. 



j Marangoni : N. Cim., (3). v. p 116,1879 (Rupert's drops of resin) ; De 

 Luynes: Phil. Mag., (4), xlv, p. 464, 1873 (Rupert's drops of glass); B. andS: 

 1. c. 



§This Journal, xxxi. pp. 441, 443: xxxii, p. 191, 1886; xxxiii, p. 33, 1887: 

 Bull. U. S. G. S., Xo. 27. pp. 30 to 50, 1886. 



||B. and S. : this Journal. III. xxxiii, p. 30. 1887. 



^Bull. U S. G. S,No. 35. p. 42. 1886. Structure studied by the density 

 method. Shells consecutively removed by galvanic solution. 



