462 THE STRENGTH 



IX. EXPERIMENT. 



In this the model of the above had one inch 

 in breadth added to its bottom rib. 



Ratio of the ribs 1 to 4f neariy. 

 Distance between supports as before. 



Dimensions of section in inches. 



Area of top rib — 1.05 x .34 = 0.357 



Do. bottom rib = 3.08 x .51 = 1.570 



Thickness of vertical part =z .305 



Area of section = 3.37 inches. 



Weight of beam = 44| lbs. 



Breaking weight=10727lbs.=95cwt. 



87 lbs. 



It broke by tension, 4 inches from the 

 middle, but slanting toward it ; and there seemed 

 to be a small flaw in the bottom rib, at the 

 place of fracture. Here tr = .6 inch. 



10727 

 3.37 



Hence strength per inch of section = 

 = 3183 lbs. Comparing this with the result 

 ofexpt. 10, gives 3 183 -2792 = 391= excess. 

 /. Gain in strength = -^ = ~ nearly. 



Remark. — Though this beam had a larger 

 bottom rib, it still broke by tension, or by 

 tearing asunder the bottom part first, as was 

 evident since it had neither been crushed nor 

 broke by a wedge, (Art. 34); this I had noticed 

 to be the case in every experiment, (see Expt. 6). 



