488 THE STRENGTH 



in strength of about yth : this beam also broke 

 by tension. Now before increasing the bottom rib 

 any further, I thought it adviseable to add a little 

 to the top one, as the vertical part of the beam, 

 or that part between the ribs would be, perhaps, 

 strong enough for much larger ribs. In expts. 

 11, 12 and 21, the top rib and vertical part 

 of the model were the same, the only difference 

 being in the breadth of the bottom rib : from 

 the first erf these the increase of strength in 

 terms of what was borne by the common beam 

 was J, from the second J, and from the third 

 J ; and had we added still more to the bottom 

 rib in the same model, it is probable that the 

 gain might have been much greater. 



-'Mi!.)! 



48. In experiments 14, 15, 16, 18, 19, and 20, the 

 top rib of the model was the same, but some- 

 what larger, than in experiments 11, J 2, and 21, 

 and the bottom rib was the only one varying. In 

 the 19th experiment the section of the bottom 

 rib at the place of fracture was more than 

 double the rest of the section, and the ratio of top 

 and bottom ribs was 1 to 6. In this instance 

 the fracture took place by the rupture of the 

 vertical part of the beam, which happened to 

 be thinner than usual; the gain in strength 

 here, from the section, was upwards of ~- of 

 what the common beam bore ; and the saving 



