198 Mr. C. Barus on Maxwell's Theory of the 



twisted, but the lower more than the upper. The results 

 under a indicate greater viscosity for the lower, a state of 

 things which is only partially wiped out by annealing at red 

 heat, in air, as indicated under b. I then commenced the ex- 

 periments proper, by leaving the upper wire untouched and 

 annealing the lower wire at red heat. The results, under c, 

 indicate an enormous difference, the unannealed wire being 

 of greater viscosity. I then left the lower wire untouched 

 and annealed the upper at red heat. The results under d 

 again show an enormous difference, the unannealed wire (now 

 the lower) being of greater viscosity. I then again annealed 

 the lower wire only, obtaining the results under e y correspond- 

 ing to c; and, finally, again annealed the upper wire only, 

 obtaining the results under/, corresponding to d. The opera- 

 tion of alternate annealing might have been continued very 

 much longer with practically the same results. In each case 

 the freshly annealed wire shows pronounced loss of viscosity, 

 as compared with an otherwise identical wire, slightly twisted 

 beyond the elastic limits. 



As compared with the effects of alloying, I found this 

 mechanical result so large as to compel me to abandon my 

 experiments on the viscosity of series of platinum alloys — at 

 least until the mechanical error in question has been inter- 

 preted and brought under control. To return to the mechani- 

 cal phenomenon in question, I may remark that the result of 

 heating a thin wire red hot in air, without precautions for 

 slow cooling, is a strain of dilatation imparted to the wire. 

 Hence molecular stability of a lower order than would obtain 

 if cooling had taken place with extreme slowness. Again, if 

 the dilated wire be twisted even over small arcs of permanent 

 set, the greater number of the more unstable configurations 

 will be mechanically broken up ; for the prevailing tendency 

 must be such as to cause these continually to fall into positions 

 of minimum potential energy. Twisting indefinitely repeated 

 therefore produces marked hardness and elasticity. 



When two wires, chemically and physically as nearly iden- 

 tical as possible, are compared, it is conceivable that viscosity 

 will vary with the time elapsed after annealing. Many ex- 

 periments were made, and showed slight increase of vis- 

 cosity with the time given to the molecules to subside after 

 annealing in air; but the results* were insignificant in 

 magnitude, often obscure, and not at all comparable with the 



* This proves that in Schroder's paper (Wied. Ann. xxviii. p. 369, 

 1886) the observed thermal " accommodation " was the result of anneal- 

 ing hard-drawn wire. 



