OF IRON BEAMS. 525 



line was so low, as appeared by the wedge in 

 experiment 19, that, J of the depth of the 

 beam was probably compressed. 



The neutral line being, therefore, within little 

 more than half an inch of the bottom flange 

 in that experiment, there could have been but 

 little there, besides that flange, submitted to 

 tension; and that little, on account of its 

 proximity to the neutral line, exerting scarcely 

 any tensile influence. 



Hence if the formula above be correct in the 

 form of section in experiment 19, it must be 

 very nearly so in forms approaching to it ; and 

 c in them nearly a constant quantity. 



» 67. We will seek, by means of the formula, 

 from each of the experiments, for the value of 

 c, when constant; and, for that purpose, con- 

 fining ourselves to those forms in which the 

 section of the bottom rib in its middle is more 

 than half the whole section of the beam, take 

 the mean from among them all for c. Since 

 then, from the formula, W z= i^, .\ c = -. 



f ad 



= -J X - . If we take the dimensions in inches, 

 we shall have, in many of the experiments, 

 5= ^ = 10.53C6; in those c = 10.5366 x •^- 



