202 



Mr. C. Bar us on Maxwell's Theory of the 



of (<£— $')/t, at two minutes and four minutes after twist is 

 imparted. These are then to be compared in their dependence 

 on current time. Phenomena of this kind were called viscous 

 " accommodation " by Streintz *, Kohlrausch f, Wiedemann J, 

 and others. 



Table V. — Viscous "Accommodation" of Glass-hard Steel. 



Twist 



Current 



No. 



time. 





minutes. 



1 







2 



24 



3 



49 



4 



75 



5 



97 



6 



118 



Xl0 : 



-1-90 

 +2-30 

 -1-20 

 4-140 

 -100 

 +1-10 



Twist 



Current 



No. 



time. 





minutes. 



7 



142 



8 



167 



9 



191 



10 



209 



11 



232 



12 



250 



xio s 



-0-75 



4-0-85 

 -0-60 

 -hO-80 

 -0-65 

 +0-70 



If, as in fig. 2 (p. 204), the numerics of A(0 — 0')/t be 

 regarded in their dependence on time, the results are seen to 

 oscillate round a mean line of equilibrium. The ordinates of 

 this mean line decrease with time at a gradually retarded 

 rate until a definite inferior limit is eventually reached. It is 

 curious to note that the largest observed ordinate (time = 

 nearly) is at least three times the limiting ordinate (time = co ). 

 After twelve twists oscillation has considerably subsided, but 

 it has not ceased ; in the same degree the viscosity of the 

 glass-hard steel rod has reached a fixed maximum. 



This complicated phenomenon (" accommodation ") is at 

 once elucidated by Maxwell's theory. The ordinates of the 

 line around which oscillation takes place are an index of the 

 degree of instability of molecular configuration at the time 

 given by the abscissae. The oscillations are the result of strain 

 (latent torsion I called it above) imparted to the configurations 

 by the successive twists to which the wire is subjected. Thus, 

 if t be the impressed twist and At the mean strain left in the 

 configurations at the instant when t is removed, and if n be 

 the original relative number of unstable configurations, and 

 An be the number broken up during the period of the strain 

 t ; then (apart from subsidiary considerations) Maxwell's 

 theory analyzes the effects of alternate twisting in accordance 

 with the following scheme : — 



* Pogg. Ann. cliii. p. 406, 1874. 



t Pogg. Ann. clviii. p. 371, 1876 ; cf. Schmidt, Wied. Ann. ii. p. 48, 

 1877. 



X Wied. Ann. vi. p. 512, 1879, 



