Temperature Coefficient of Young 7 s Modulus. 377 



Although fig. 2 is purely diagrammatic, the curves A 

 and B (fig. 1) are actually plotted from the values o£ 

 Young's modulus derived from the hypothetical graphs of 

 fig. 2. A and B are, however, on different scales. 

 % The whole issue is thus reduced to the question : Are the 

 load elongation graphs at different temperatures straight 

 lines or not throughout the total range of stress ? If they 

 are there can be no maximum in the modulus temperature 

 curve. 



Experiment 1. 



N The iron wire, mounted in the apparatus, was annealed at 

 400° under a tension of 20 kilos /sq. cm. The relation 

 between load and elongation was then found at temperature 

 intervals of 5° or 10° between the limits 27° and 150°. 

 Special attention was paid to the interval 40° to 60° where 

 a maximum in the modulus has been observed by Walker, 

 The total load on the wire was never less than 20 kilos / sq. mm. 

 The load elongation graphs are all obviously straight lines 

 within the limits of experimental error, and in every case the 

 " best line " through the points was obtained by the Method 

 of Least Squares. 



Two of the lines are shown in fio\ 3. 



1-5 



Fig. 3. 



Tempera, ture 82 ° C 



Temperature 54-^ C 





3 

 Load 



3 4- 



Load 



After the complete series of graphs had been drawn, the 

 stretch for a particular load at each of the temperatures was 

 found from the equation to the line; the series of elongations 

 thus obtained yields the variation in Young's modulus with 

 temperature throughout the range 



The curve is given in 



