Viscosity of Solids and its Physical Verification. 185 



view to be advocated ; and it was the direct bearing of some 

 of the results on Clausius's theory of electrolysis, that led me 

 to suspect a chemical explanation *, before I became aware of 

 the existence of Maxwell's article. To show how clearly 

 Maxwell's theory interprets the complex and almost anomalous 

 phenomena of viscosity exhibited by tempered steel, is the 

 chief endeavour of the present paper ; but 1 shall also add 

 other matter. 



2. It is desirable to pass in brief review the divers hypotheses 

 on the nature of viscosity in solids, to which I have referred. 



0. E. Meyer's theory f is the earliest and the most direct. 

 It discusses the action of elastic forces in a medium of im- 

 perfect elasticity, and develops formulae to express the 

 diminution of stress in virtue of the occurrence of internal 

 friction J. The results to which Meyer's theory eventually 

 leads are incomplete, and were not fully verified by subsequent 

 experiment. The theory is therefore sharply antagonized by 

 Boltzmann §, by Streintz ||, and by Kohlrausch H. In a 

 later paper Meyer ** partially assents to these adverse views, 

 acknowledging that the theory does not reproduce the 

 phenomenon actually observed. It also fails, as Kohlrausch 

 (I. c.) pointed out, in predicting an insufficiently slow time of 

 occmreuce. After giving reasons for dissenting from Boltz- 

 manirs and from Neesen's hypotheses, Meyer proceeds to a 

 partial development of an old hypothesis of Weber ft- This 

 physicist referred viscosity in solids to partial molecular 

 rotation, a view adopted by Kohlrausch +|, by whom it has 

 been more clearly interpreted. The rotations underlying 

 Weber's phenomenon are considered identical with the 

 rotation of molecules postulated by Clausius §§ in discussing 



* Am. Journ. [3] xxxiii. p. 28, 1887. It is much to be regretted that 

 Maxwell's theory was published out of the line of a physicist's usual 

 routine reading. 



t Meyer, Pogg. Ann. cli. p. 108, 1874. 



| Following the usage of the word by Navier, Cauchy, Poisson, St. 

 Tenant, Stokes, Stefan. Cf. Meyer, I. c. 



§ Pogg. Ann. Eiganzb. vii. p. 624, 1876. 



j| Pogg. Ann. civ. p. 588, lte75 ; ibid, cliii. p. 405, 1874. 



51 Pogsr. Ann. clx. p. 225, 1877. 



** Wied. Ami. iv. p. 249, 1878. 



tt Weber, Pogg. Ann. xxxiv. p. 247, 1835 ; ibid. liv. p. 1, 184]. 



XX Pogg. Ann. exxviii. p. 413, 1866 ; cf. also ibid. cxix. p. 337, 1863 ; 

 ibid, clvifi. p. 337, 1876. 



§§ Clausius, Pogg. Ann.lxxvi. p. 46, 1849. Shearing stress is referred to : 

 11 Wenn ein solcher Kbrper fremden Kraften unterworfen wird, die von 

 veschiedenen Seiten un^leich auf ihn wirken, er also z. B. nach eincr 

 Dimension gedehnt wird, wahrend er nach anderen Dimensionen frei 

 bleibt oder gar zu.-ammengedruckt wird, dann die Molekiile neben ihrer 

 hiebnng ^ch audi etwas drehen kcinnen, indem sie in Bezug auf 

 ihre Kraftrichtungen den ungleichen Spannungen etwas folgen . . ." (p. 66). 



