OF IRON BEAMS. 435 



laid on at C. Hence, since the depth of the 



casting was 1.35 (expt. 4), CD = ^ depth = — 

 of it nearly. 



This experiment is interesting; it shews 

 the situation of the neutral point, and may from 

 the peculiar form of the wedge, throw some 

 additional light on the nature of the strain. 



The other casting bore 2} cwt. and broke 

 with 2i cwt. 



The strength of the castings was therefore as 

 8 J to 2 J, or as 4 to 1 nearly, according as they 

 were broke, one or the other way upwards. 



Those, who suppose the strength to be 

 bounded by the elasticity, and that the same 

 force would destroy the elastic power, whether 

 it tended to extend or compress the body, 

 must have conceived these castings, and indeed 

 those of every other form, to be equally strong, 

 which-ever way upwards they were turned. 

 A conclusion which we see would lead to very 

 erroneous results, if applied to measure the 

 ultimate strength of cast iron. 



24. When I had proceeded thus far, I shewed 

 the results to Mr. Ewart, and mentioned to 

 3i 2 



