OF IRON BBAMS. 469 



with the bottom rib, the beam might be made 

 of equal lieight throughout, and consequently 

 its depth, and power of bearing near the ends^ 

 increased with little additional metal. 



From the form of fracture in the preceding 

 experiments, and the great size which the 

 bottom rib would be of, I was convinced that 

 the neutral line in our future experiments would 

 lie very low,* and, therefore, nearly all thd 

 tensile force would be exerted by the bottom 

 rib, whilst the rest of the beam would serve 

 for little more than a fulcrum 5 the center t»f 

 resistance to compression, or of that fulcrum, 

 laying very near to the top, it being perhaps 

 at the point r in our former experiments. 



'"Suppose D to be the Vertical distance from 

 the center of compression, at any part of the 

 beam, to the center of tension in the bottom 

 rib ; and if T be the direct tensile strength of 

 the bottom rib at that part, T multiplied by 

 some function of D, (perhaps T x D) will 

 represent the strength of the beam there* But 



but that was neglected as there inight have been too great a 

 tendency in the weight to cut the beam across near to its enda, 

 if it were more reduced there ; see Article 33. 



• This was verified by the 19th experiment, where the 

 wedge shewed the neutral line to be at | of the depth. 



