OF IRON BEAMS. 465 



DlmentioM of tection. 



Area of top rib = 1.6 X .315 = 0.6 inches. 



„ bottom rib =4.16 X .53 = 2.2 „ 



Thickness of vertical part = .38 „ 



Area of section = 4.50 inches. 



Weight of beam = 57 lbs. 

 Deflection with 11186 lbs. .4 inches. 

 12698 „ .46 „ 

 13706 „ .52 „ 

 Breaking weight = 14462 lbs.= 129 cwt. 14 lbs. 

 It broke by tension 1 inch from the middle j 

 bn = 2-5 inches. 



Hence strength per inch of section = ^ ^ 

 = 3214 lbs. Comparing this with the result of 

 experiment 13, which bore 2693 lbs. per inch, 

 3214 - 2693 = 521 = excess. 

 /. Gain in strength ^ = — nearly. 



We may seek for the gain by comparing the 

 weights of the two beams, and the quantities 

 they bore: thus, since in experiment 13, the 

 weight of the beam was 41 lbs., and it broke 

 with 8942 lbs, and the weight of this beam 

 57 lbs,, and its breaking weight 14462 lbs. 

 Hence 41 : 57 :: 8942 : 12431 = weight 

 this beam should have borne, according to the 

 strength of the common beam; but it did 

 bear 14462. .'. Gain = 14462 - 12431 = -f 

 nearly. 



3 N 



