242 FIRE-BOX GIRDER STAYS. 



And this is the Board of Trade equation 



833-3 X ^^ X ^ 

 {W-P)xDxWPxL 



in which the constant factor c = 833-3 for girders with four 

 supporting bolts. The constant c in the Board's Rule is 

 given as — 850. This is not strictly accurate, the exact figure 

 is 833 3 ; but the Board have adopted the constant 850 

 because it is a round number easily remembered and suffi- 

 ciently accurate for all practical purposes. 



^.■- 



