357 
and strength of hard and soft steel, 
lbs. inches. 
with a load of 18.6 the depression in the middle was 0.05 
37.0 ------- 0.10 
47.0 ------- 0.127 
The bar was then hardened, so that a file made no impression 
on any part of it, and the same loads did not produce flexures 
that were sensibly different from those in the soft state. 
I then lowered the temper till it assumed an uniform straw 
colour ; 
lbs. inches. 
when with a load of 47 the depression in the middle was 0.127 
85------ - 0.230 
130 ------- 0.350 
150- - - - - - 0.400 
The load of i5olbs. produced a permanent set of 0.012, but 
i30lbs. produced no sensible effect. The loading was con- 
lbs. Inches. 
tinued, and with 185 the depression in the middle was 0.50 
38 5 ------- 1.04 
When 385lbs. had been upon the bar about a minute, it 
emitted a faint creaking sound, and consequently I ceased to 
add fresh weights ; in about fourteen minutes the bar broke, 
exactly in the middle of the length. 
On comparing the fractures of the specimens, there was no 
apparent difference except in colour. The grain was fine, 
and equal ; the small sparkles of metallic lustre abundant, 
and equally diffused ; but in the harder specimen they had a 
whiter ground. 
From these experiments it appears that the elastic force of 
steel is sensibly the same in all states of temper. 
The height of the modulus of elasticity, calculated by the 
