356 Mr. Tredgold's experiments on the elasticity 
The temper of the bar was then lowered to a rather deep 
straw yellow, and it was tried again ; when the same loads 
produced exactly the same flexures as before. 
The temper was then lowered till the colour was an uni- 
form blue, or spring temper ; and the trials were repeated 
with the same loads ; but the flexures were still the same. 
It was now heated to redness and very slowly cooled. In 
this state the same loads still produced the same flexures ; 
and the load of no lbs. caused no permanent change of form. 
The bar was hardened again, and made very hard ; in this 
state the same loads produced the same flexures ; and 
lbs. inches. 
with a load of 300 the depression in the middle was 0.115 
350 - 0.130 
5 80 - - broke. 
When the bar was relieved from the load of 350 lbs. it re- 
tained a permanent flexure of 0.005 inches, which increased 
to 0.01 with the addition of 10 lbs. to the load. 
I found that a bar of much greater length might be tem- 
pered without difficulty, and therefore had another bar made 
of the same kind of steel ; the length of which being 25 inches, 
about double the flexure could be given with the same strain 
upon the material, and therefore any small degree of differ- 
ence in the elastic force might be more easily detected, for 
the preceding experiments are sufficient to show that if there 
be any difference, it must be extremely small. 
The breadth of this bar was 0.92 inches ; the depth 0.36 
inches ; and the distance between the supports 24 inches. It 
was soft, so as to yield easily to the file. 
