612 THE STRENGTH 



the middle by tension with this weight, after 

 having borne it about a minute. 



28168 



Hence strength per inch of section = -y^ = 

 3565 lbs. To compare this w^ith the results 

 from the beam of common form ; the mean 

 from experiments 4 and 34, gives 2796 lbs. 

 per inch, (see end of experiment 28). 

 .'. 3565 - 2796 = 769. 



Hence saving in metal from section = ^^ = 

 .215 lbs. 



^' If we compare the weights of the same beams, 

 as in experiment 28, the saving will be .307, 

 or upwards of Vo of the metal ; which is the 

 whole saving both from the section and the 

 form of the beam near its ends. 



XXXII. EXPERIMENT. 



Distance between supports, 9 feet. 

 Depth of beam, 5f inches. 

 Weight of beam, 192 lbs. 



DimeosioDs of section, (fig. experiment 38.) 



Area of top rib 2.25 x .3 =: .67 inches. 

 Area of bottom rib 7.7 x .76= 5.85 „ 

 Thickness at A = .36 

 at B = .42 

 at C = .50. 



