C. Bar us — Viscosity of Solids. 207 



in all degrees of magnetic intensity. Stability and intensity 

 are the qualities which in the present case correspond to 

 stability and strain, respectively, in the above configurations. 



Magnetic stability decreases from hard to soft and from soft 

 steel to soft iron, following therefore the inverse order of 

 viscosity ; and its character too is different from viscosity, the 

 tendency being toward sudden magnetic changes, even when 

 the cause of such change is superinduced by heat. Cf. § 19. 



The mean magnetic intensity of the configuration must de- 

 pend on the dimensions of the saturated rod. In the normal 

 case of linear rods this magnetic intensity increases from hard 

 to soft steel* and from steel to iron. Hence from one point 

 of view carbon configurations interfere with the occurrence of 

 intense magnetic configurations ; from the other point of view 

 magnetic intensity increases in the direct order of viscosity, or 

 stability of molecular configuration. 



Among methods for elucidating the nature of the magnetic 

 configuration, a comparison, of the effect of a magnetic field on 

 torsional rigidity is probably best. Extending the classic re- 

 searches of G-. Wiedemann, f I commenced a series of such 

 measurements. In the case of a given field of great intensity, 

 if two identical iron wires, respectively magnetic and unmag- 

 netic, be counter-twisted to the same maximum shear (obliquity 

 of external fibre, <w='003, say), then the product of the detor- 

 sion due to longitudinal magnetization and the diameter of the 

 wires is constant and equal to the product of the shear and the 

 magnetic coefficient of rigidity. This remarkable relation im- 

 plies that the increment of the twisting couple evolved by 

 magnetization increases as the third power of the radians, ccet. 

 par. 



21. Summarizing the results of the above paragraphs, I 

 believe the statement of § 2 to be fully verified. I have shown 

 that the effect of distributing unstable molecular configurations 

 uniformly throughout the substance of a rigid metal, like steel, 

 is analogous to that of dissolving molecules of acid or of salt in 

 a non-conductor like water. These added molecules are the 

 unstable groups with which Clausius's theory deals. In both 

 cases the effect produced is proportional to the number of 

 unstable groups distributed. If the number be sufficiently in- 

 creased, the medium will ultimately be a viscous fluid in the 

 one case, and an electrolytic conductor in the other. At the 

 outset, pure water typifies the rigid solid. 



* S. and B. : Wied. Ann., xx, p. 621, 1883. 



f Wiedemann: Electricitat, III, p. 6S3 to 698, 3d ed., 1883; Barns: this Jour- 

 nal (III), xxxiv, p. 180, 1887. I believe my researches are the first attempt to 

 interpret these relations quantitatively, and they lead to the law expressed in the 

 text. Other results I will communicate later. 



