On the Effects of Changes of Temperature on Metal Wires. IS!) 



G'000447 and 0*000428 respectively. The result given above for com- 

 mercial copper agrees also moderately well with that obtained by these 

 experimenters, viz., 0'000520. But here, as indeed in all the substances 

 examined, the differences in results are not surprising, in view of the 

 probable difference of composition of the specimens. 



The great excess of the coefficient in the case of hard-drawn pure 

 copper above the value for commercial copper is very noteworthy. It 

 will be interesting to examine, as we propose to do immediately, the 

 behaviour of copper wire soft drawn as well as hard, and to trace the 

 effect, if any, of repeated heating and cooling. 



It was noticed that the rate of dying out of the torsional oscillations 

 was very different at the different temperatures, being, except in one 

 case, that of German silver, very much more rapid at the higher tem- 

 perature than at the lower. This is undoubtedly the effect of a con- 

 siderable increase of the internal viscosity of the wire with rise of 

 temperature, for no practical difference existed in the immediate sur- 

 roundings of the vibrator, which of course was the part mainly affected 

 by the air in the vibrations. The top of the cylindrical vibrator in 

 each case was about 8 cm. below the lower end of the heater, and the 

 length of the cylinders, which were of brass, varied from 7 to 13 cm. 

 There was no appreciable change of the air-temperature at the vibrator 

 produced by the heater. 



This difference in the rates of subsidence of the torsional oscillations 

 seems to us very remarkable, and, so far as we know, has not been 

 observed before. It is shown in the diagrams numbered I VI. 



\Xote added June 20, 1900. The change in rate of subsidence pro- 

 duced by alteration of temperature had, we have since found, been 

 observed by Streintz and by Pisati (' Pogg. Ann.,' 153, 1874, and 

 ' Gazzetta Chimica Italiana,' 1876, 1877, also ' Sitzungsb. cl. Wien. 

 Akad.,' Ixxx, Abth. 2, 1879). In the first and last papers here cited, 

 Streintz gives an account of his own work and of that of Pisati, 

 principally as bearing on the effect which he called " Accommodation." 

 In certain wires, e.g., steel, copper, silver, brass, and platinum, 

 examined by Streintz and Pisati, a marked diminution of rate of 

 subsidence was produced by keeping the wire for a considerable 

 time in continual torsional oscillation. This is contrary to results 

 obtained by Lord Kelvin at an earlier date, 1864-5 (Art. " Elasticity," 

 < Collected Papers,' vol. III). 



Since learning of the investigations here referred to, we have begun 

 to extend our experiments to the question of " fatigue of elasticity," 

 and have found that the rate of subsidence appears to be, in some 

 cases at least, a function of the temperature and of the amplitude of 

 vibration. It seems possible thus to reconcile the discordance of re- 

 sults thus referred to, and we hope to make a communication on the 

 subject at an early date.] 



