OF IRON BEAMS. 433 



often been assumed by writers, but I have not 

 before seen any proof of it, except in an 

 experiment of M. Duleau, which renders it 

 very probable that it is the case in malleable 

 iron. Mr. Tredgold in his "Essay on the 

 Strength of Cast Iron" has assumed it, and 

 made it the basis of his reasonings. He thence 

 concludes (Section 4th,) that in a beam of the 

 strongest form, its section ought to have equal 

 ribs at top and bottom of it : so that the 

 neutral axis being at half the height of the 

 beam, there might be equal resisting powers 

 on both sides of that axis. Another conclusion 

 which might be drawn in the same way, and 

 which he mentions (page 132) is, that a 

 triangular prism [he might from his view have 

 said any other form] is equally strong, whether it 

 be loaded one way up or the opposite, supposing 

 it not strained, so as to injure its elasticity. ^ 



22. This is perhaps not a full view of the 

 matter : Mr. Tredgold reasoned on a supposition 

 that the same force, which would destroy the 

 elasticity of a body by tension, would destroy 

 it by compression ; but it is highly probable, 

 as will be shewn further on, that in cast iron 

 a much larger force is required in the latter case 

 than in the former. An experiment, which I 

 am going to describe, suggested this to me ; it 



3 I 



