IN TORSIONAL OSCILLATION 



127 



The behaviour of b after the wire has been heated, and 

 fatigued will be the object of further work. 



3. A length of brass wire, clamped vertically between C 

 and D, and fatigued for two and a half hours, gave the values 



a=90, w=-76, 6=841. 



These are the values got for the original wire, and thus exten- 

 sional fatigue has no effect on the constants when the wire 

 is unheated. This was confirmed by further experiments. 



4. After heating to a red heat and then cooling, exten- 

 sional fatigue was found to have the same tendency as stretch- 

 ing had i.e. to tend to straighten the curve so as to allow 

 of one straight line representing the results. A typical experi- 

 ment gave the values 



a=30, 7i=l-24, 6=524. 



This wire was fatigued for one hour after having been 

 raised to 485 C. It was found that the pendulum made 

 twenty-five complete oscillations per minute ; therefore, since 

 the wire between C and D receives two pulls during one oscil- 

 lation, the total number of pulls given was 3000. The weight 



1 This value, 3 '36, got for the line lying along the points of the first oscillations, is 

 quite abnormal, and the wire used in this experiment was examined to discover, if 

 possible, the cause of the unusual value of n. A repeated experiment gave the same 

 result. The wire was then halved, each half being tested separately, and finally the 

 abnormality was traced to one of the quarters. 



