420 THE STRENGTH 



12. This last observation of M. Duleau is right, 

 as regards wood or malleable iron; but the case 

 is very different in cast iron. It will be indis- 

 pensibly necessary for us to use some general 

 principle, as that above, if correct; since nearly 

 all the forms in the following pages are different 

 on the two sides of the neutral line. 



13. M. Duleau, having (at pages 26 and 27) 

 found that a triangular piece of malleable iron 

 was equally bent by the same weight, whether 

 the edge or the base was uppermost, comes to 

 the following conclusion : — *' This piece whether 

 placed upon a, face, or an arris, presents the 

 same resistance: it follows from thence, sup- 

 posing the line of passage from tension to 

 compression to be a right one, that in a trans- 

 verse section of the piece, the sum of the 

 moments of the compressed fibres, and that of 

 the moments of the extended ones are equal.*' — 

 This conclusion, if correct, would be a proof 

 of the preceding principle, and is offered as 

 such by M. Duleau. — ^With great respect for 

 that writer's judgment, I must however draw 

 a different conclusion. It appears to me that 

 the experiment shews the extensions and com- 

 pressions to have been equal from the same 

 forces, and as the forces; the situation of the 



