441 



•. In order to increase the arm CD of the 

 lever, and consequently the strength of the 

 beam, the parts should be disposed as far 

 asunder as possible. Tiiis would j^erhaps be 

 best effected by putting two strong ribs, one at 

 top the other at bottom, the intermediate part 

 between the ribs being a thin sheet of metal to 

 keep the ribs always at the same distance, 

 and thereby prevent derangement from irregular 

 strains, as well as to serve another purpose 

 which will be mentioned further on. 



30. As to the comparative strength of these 

 ribs, that appears to me to depend upon the 

 nature of the material, and can only be derived 

 from experiment. Thus, suppose it was found 

 that it required the same force to destroy the 

 elasticity of a piece of metal, whether the force 

 acted by tension or compression. In this case, 

 the top rib ought to be equal to the bottom 

 one, supposing it was never intended to strain 

 the beam so as to injure its elasticity. And if 

 it were found that the same weight would be 



3 K 



