442 THE STRENTGH 



required to tear asunder or to crush a piece 

 of metal according as it acted one way or the 

 other, the beam should have equal ribs to 

 enable it to bear the most without breaking. 

 Now, from the experiments given above, it 

 appears, that these quaUties are in a great 

 measure possessed by wrought iron ; and there- 

 fore, whether it was intended to strain a 

 beam of it to the extent of its elasticity or even 

 to the breaking point, there ought to be equal 

 ribs at top and bottom. 



31. If, however, the metal were of such a 

 nature that a force, F, was needed to destroy 

 its elasticity by stretching it, and another 

 force, G, to do the same by compressing it, 

 it is evident that the ribs ought to be to one 

 another, as F to G, in order that the beam 

 might bear the most without injury to its 

 elasticity. And if it took unequal weights, F', 

 and G', to break the piece by tension and 

 compression, the beam should have ribs, as F' 

 to G', to bear the most without fracture. 



Our experiments on cast iron were not well 

 adapted to shew what relative forces would be 

 required to destroy the elasticities; but it 

 appears, by the experiments of Mr. Rennie, that 

 it would take many times the force which w^ould 



