August 29, 1902.] 



SCIENCE. 



337 



rigidity modulus, and (t Poisson's ratio, 

 the theory of elasticity gives, for au iso- 

 tropic solid, 



_ JE— 2)8 

 2ft ■ 



Now for most metals E is about two and 

 one half times n. Hence it is evident that 

 a small error in the determination of E or 

 11 may be quite a large error, in the in- 

 ferred value of T. 



The results of the experiments in general 

 were that for steel either hardrolled or an- 

 nealed the results given by the above for- 

 mulae and those got by direct measurement 

 are almost identical. In the cases of cast 

 iron and alloys of the metals, however, the 

 results obtained from the formulas are not 

 reliable. The following short table illus- 

 trates the results obtained by direct meas- 

 urement : 



fore the American Society of Mechan- 

 ical Engineers by Professor C. H. 

 Benjamin. The principal subject in 

 that paper was the resistance to compres- 

 sion of helical springs. Incidentally it was 

 stated that the modulus of rigidity derived 

 by calculation from these experiments was 

 much higher than that usually given in the 

 published data for steel. This seemed con- 

 trary to my experience, but on looking for 

 direct evidence on the subject no record 

 could be found. In consequence a few 

 specimens of steel, containing different 

 amounts of carbon, were prepared and 

 tested directly for rigidity in their original 

 state, and also after hardening by heating 

 to redness and quenching in water. The re- 

 sults are given in the tabular form below. 

 The percentages of carbon in these speci- 

 mens were not determined as the exact 



Effect of Hardening on the Rigidity of 

 Steel: Professor Thomas Gray. 

 Attention was called to this subject 



some months ago in a paper read be- 



amount did not seem of any importance. 

 fSpecimen No. 3 had just carbon enough to 

 admit of hardening. 



The results show the effect of hardening 



Kinds of Steel. 



High carbon tool (soft) 



High carbon tool (hardened) 



Medium carbon tool (soft) 



Medium carbon tool ( hardened ) 



Low carbon tool (s<^t) 



Low carbon tool (hardened) 



Low carbon tool (blue tempered) 



Special tool 1.5 per cent, carbon (soft) 

 Special tool 1.5 per cent, (hardened) . 



