C 354 ] 
XVIII . Experiments on the elasticity and strength of hard and 
soft steel. In a Letter to Thomas Young, M. D. For. Sec. 
R. S. By Mr. Thomas Tredgold, Civil Engineer. 
Read March 25, 1824. 
Sir, London , Dee . i 6 , 1823 
If a piece of very hard steel be softened, it is natural to 
suppose that the operation will produce a corresponding 
change in the elastic power, and that the same load would 
produce a greater flexure in the soft state than in the hard 
one, when all other circumstances were the same. Mr. Cou- 
lomb inferred from some comparative experiments on small 
specimens, that the state of temper does not alter the elastic 
force of steel ; and your Experiments on Vibration led to 
the same conclusion (Nat. Philos. II. 403). But the subject 
appeared to require further investigation, and particularly 
because it afforded an opportunity of ascertaining some other 
facts respecting steel, which had not been before examined. 
In making the experiments which I am about to describe, 
each bar was supported at its ends by two blocks of cast 
iron. These blocks rested upon a strong wooden frame. 
The scale to contain the weights was suspended from the 
middle of the length of the bar, by a cylindrical steel pin of 
about -Jths of an inch in diameter. And as in experiments of 
this kind it is desirable to have the means of raising the 
weight from the bar, without altering its position, in order 
to know when the load is sufficient to produce a permanent 
change of structure, I have a powerful screw with a fine 
