630 THE STRENGTH 



Distance between supports 26 ft., or 312 ins. 



Depth of beam, in middle, 21 i inches. 



Area of section of bottom rib, in middle, 

 16 X 3 zi 48 inches. 



Form of section, of beam, nearly the same 

 as in experiment 30. 



Referring to the formula we have, /=:312, 

 d=z 27.5, a = 48. 

 .-. W, the breaking weight, =^^><Ip<A^^l><±^^ ^uq tons. 



These beams are intended to bear the same 

 weight in every part; they will not however, 

 be quite of uniform depth throughout. The 

 load will have to lie upon their bottom rib, 

 through its whole length ; it becomes necessary 

 therefore to make that_ rib somewhat broader, 

 toward the ends, than according to the parabolic 

 form described after experiment 13; and this 

 enables the depth of the beams, near their 

 ends, to be a little reduced. 



72. The views developed in this essay, if 

 correct, must, as appears to the writer, have an 

 influence on the forms of cast iron wherever 

 it is intended for bearing purposes. In all the 

 preceding experiments, the beams were designed 

 to bear the same weight uniformly distributed 

 over them; but were always, except otherwise 



