ON IRON BEAMS. 417 



For examples see my paper on the strength of 

 materials referred to above. 



10. These theorems can with propriety only 

 apply so long as the elasticity is but little im- 

 paired, and in cast iron must be used only during 

 that time ; as afterwards, the shifting of the 

 neutral line would alter the value of s and lead 

 to error; as will be seen from an example to 

 the 2nd Corollary, taken from an experiment 

 of Mr. Tredgold. (Essay on strength of cast 

 iron, section 5, page 83). 



A rectangular bar of old park iron, depth 

 0.65 inches, breadth 1.3 inches, fixed in a 

 horizontal position at one end, broke by a 

 weight of 184lbs. at the other, leverage 2 feet. 

 Now as about j of the breaking weight would 

 destroy the elasticity in a rectangular piece, 

 (Tredgold, page 79), quere, what was the strain 

 per inch on the top of this bar, or the value of 

 if when the weight of 60lbs, was laid on it? 



o* iM^ 4 GUo 6x24x60 



Smce w = ^, .-. ^ = ^= ,.3x.65x.65 = 157301bs. 



per inch. — Mr. Tredgold, from the mean of his 

 experiments, makes the quantity that would be 

 required to destroy by direct tension the 

 elasticity of a piece of cast iron, whose section 

 was an inch, 15300lb$.; which is somewhat 



3 o 



