and Strength of Materials. 279 
answer.—The depth of the extended surface 
being then to that of the compressed from a 
mean of our experiments on oak, as 27 to 
31, or as7to 8 nearly, we have 7+8:7:: 12 
(the depth) : 76 = 5.6 inches=a; ., A=5°6 
56 2 
X12= 67.2; g= 5 ptp'=>x12—8, and 
L= sgt? 10 feet = 120 inches ; and the for- 
36 
8000x —x67.2x8 
sgAx (p+p’) 2 
mala, -—~;--— becomes 56120 
17920 pounds = the pressure at the end ; and 
17920 2 = 35840 pounds — the weight at its 
middle. 
Remark.—These two questions would have 
been solved with greater simplicity by Cor. 
3d, art. 15th, but it was preferred to give 
them as examples to the more general theo- 
rem above. 
Example 3d. Supposing 8000 pounds to 
the inch to be the full direct cohesion of the 
piece, and the position of the neutral line, 
as determined in the last example, to be that 
of fracture, to determine the weight to. be 
laid on the middle of that piece, when we take 
into consideration the decreasing energies of 
the forces of extension and compression ? 
Referring then to the general formula for 
the strength of a joist.— 
