OF IRON BEAMS. 425 



which would have been unbent, when those 

 which are in the instrument were so, and which 

 (when bent so that the trianglcj might assume 

 the position it was in during the experiments,) 

 would exert equal forces to the weights w, i«/, 

 &c. themselves; and, therefore, LM may be con- 

 sidered as the line of the fracture of a beam, 

 whereof ELM is a vertical section, the central 

 spring on which the triangle turned being its 

 neutral line, and the springs and weights on 

 each side of it representing the forces of tension 

 and compression ; which, from the experi- 

 ments above, have no particular relation to 

 their distances from the neutral line, but must, 

 under all the circumstances, be equal. 



17. My next object was to seek, experimen- 

 tally, for the laws which connect the extensions 

 and compressions with the forces in ca^t 

 iron, through their whole range, to the fracture 

 of a bent piece. 



For this purpose, I got several castings 

 moulded of different sizes, but of one general 

 form, such that by bending them, first one 

 way and then the other, the relative resistances 

 to extension and compression in one and the 

 same part might be obtained. Each casting 

 was several feet long, and equal in section 

 3 H 



