[coKER à M'KBRGOw] THERMAL CHANGE TO TENSION 



19 



radiation and conduction will vary, for if an instantaneous load be 

 apjjlied to a bar producing a thermal change of ^o, then if A be the 

 heat loss in unit time due to unit temperature difference, then we have, 

 using our previous notation — 



dO = — kOdt 

 dd 



or 



6 



= — k-dt 



and hence the temperature at any subsequent time is 



— kt 



or if we neglect quantities involving k-, we arrive at a correction for- 

 mula of the form 



^a = ^o (1 + ^0 



or the correction is twice that found for a gradually applied load. 



In order to test the approximate correctness of the above formula 

 for such cases, some preliminary experiments were made, in, which a 

 definite heating effect was applied to a test piece for different intervals 

 of time. Figure 6 shows the arrangement used, where the ends of a 



O O 



L L 



thin strip of steel B are joined up in a circuit containing an adjustable 

 resistance E, and an ammeter A. A thermo-pile T pressed against the 



