126 



THE DISSIPATION OF ENERGY 



unheated state ; and (4) to extensional strain after raising to 

 a red heat and then allowing to cool. 



1. Wires were fatigued in this manner for periods vary- 

 ing from five minutes to three and a half hours, and subse- 

 quently tested. The values got were as follows : 



The value of n is seen to remain constant over this range 

 of fatigue, whilst that of a oscillates about 100, the values of 

 a when large being more uncertain than when small, since in 

 trying to find the best value of a, values of the latter differing 

 by ten or twenty units may make very little difference in the 

 slope of the line, or the possibility of the points lying along 

 it ; b seems to be the only constant affected. It has already 

 been seen that the value of b is very variable, but there 

 appears to be a gradual fall in value here, however. Rota- 

 tional fatigue, then, has little or no effect on the constants 

 of the equation. Further work will be directed to ascer- 

 taining if this fall in the value of b with increase of fatigue 

 is invariable and therefore real. 



2. It was shown above that after brass wire had been 

 raised to a temperature above 375 C., two values of n were 

 obtained, one value extending over one range of oscillation, 

 and another over the remaining part. It was shown also 

 that these values of n increased to a constant value. Fatigue, 

 induced by rotational strain, is again found to have no 

 effect on the constants a and n, as the following results 

 will show : 



