4S2 THE STRENGTH 



40. Tlie first six beams in the first series were 

 cast horizontal, that is, eacli beam lay fiat on 

 its side in the sand ; all the rest were cast 

 erecty that is, each beam lay in the sand in 

 the same posture as when it was afterwards 

 loaded, except that the casting was turned 

 upside down, when in the sand. 



In all the experiments the area of the section 

 was obtained with the greatest care ; it includes, 

 besides the parts of which the dimensions are 

 given, the area of the small angular portions 

 at the junction of the top and bottom ribs with 

 the vertical part between them. 



41. The principal objects proposed in the 

 experiments were: first to seek, directed by 

 theory, for the form of section, in which a 

 cast iron beam would be the strongest, up to the 

 time of fracture, its length and depth being 

 given : next to obtain, if possible, a general 

 rule for the strength of such a beam then, since 

 the rules given in the commencement of this 

 paper only apply, in cast iron, so long as the 

 elasticity is perfect: see Article 10. 



