482 THE STRENGTH 



the tensile power of this form of section almost 

 wholly lies, was not much different. The iron 

 must therefore have been weaker. 



Strength per square inch of section = -^-r- 

 = 3576 lbs. 



Comparing this with the result of the common 

 beam in experiment 22, which bore 2885 lbs. 

 per inch, 3576 - 2885 = 691 zz excess. 



691 



.*. Gain in strength, from section, = ^^ =. .236, 

 in terms of what the common beam bore; whence 

 saving in metal = ^^ = J nearly. 



If we compare this beam with the common 

 one, by their weights, the saving in metal will 

 be .26, or upwards of Jth. 



The thickness of the vertical part of the beam, 

 in experiment 19, was .266, and in this expt, 

 .335; we might therefore have increased the 

 bottom rib of this beam, in the ratio of 335 to 

 266, or jrd nearly, when it is probable the 

 beam would have broke equally soon by tension, or 

 by the rupture of the vertical part as in experiment 

 19. — And a much greater excess of strength 

 than that above would have been obtained. 



XXJ. EXPERIMENT. 



lOfThis was on an elliptical beam from the same 

 model as that in experiment 12, and those 



