236 PROFESSOR E. G. COKER ON 
be seen that the extension for all the different loads below the yield point of the 
material are practically constant. This is shown graphically by fig. 3, in which the 
readings are plotted as ordinates, with the temperatures as abscissee. The curves for 
stresses below the yield point are very nearly straight lines, with the exception of 
No. IV., when a load of 3000 pounds was applied, corresponding to a stress of 28,790 
pounds per square inch. We may neglect the small deviation there shown, since at an 
increased stress of 33,570 pounds per square inch it disappears, and we may assume 
that the expansion is practically linear. The mean value of the coefficient of expansion — 
for these five different experiments corresponds to a linear expansion of ‘00001953 for 
1° centigrade, the maximum deviution therefrom being slightly less than 1 per cent. 
For the overstrained tube the coefficient of expansion was greater, the values 
obtained being as follows :— 
TaBie II. 
Total Permanent Extension. Coefficients of Expansion per 
Inches. 1° Centigrade. 
ae 00001963 
4 00002004 
4 00002121 
A similar experiment upon a steel tube having very thin walls was made, and the 
results are given in Table III. 
