4,5
of Saillancourt stone, of which this bridge is con-structed, weighs 152 French pounds; that a cubicfoot will just bear a column of the same material 1580feet high ; that the radius of curvature at the vertex(originally 150 feet) of the arch, after it had takenits bearing, to be 244 feet, and the height of the keystone to be five feet (French measures) c — 244,
n—5, »■= 152lbs., f = 1580, w' = n (■£- - 1 ) =
n [1^2- 1 ) —5 x 5, 475 = a prismatick column of the
' 244
same material, one square foot base, 27.4 feet high,and 27.4 x 152 = 4165 lbs. French , on a foot super-ficial, which is the limit of weight the bridge is ca-pable of sustaining at the vertex. To find the weightin English avoirdup. pounds on an English foot, as12.78 2 : 12 2 :: 4165 : 3672 French lbs. on an English foot. Then, as 7000:7561 :: 3672:3966 English lbs. avoird. on an English foot.
(Cornish Granite.)
c = 112.5 feet, n = 5 feet, g = = 166.4 lbs. j’
— 5502 feet, to' ~n - l) = n ~ 1 ) ~ 5 x
47.9 = a prismatick column of the same material 239-5feet high of one square foot base, and 239-5 x 166.4 =39846 lbs. avoirdupois on a superficial foot, which isthe limit of weight the bridge is capable of sustainingat the vertex.*
* The same may be determined directly in lbs. as follows:c=112,5 g =. 2 22?_= 2.6 Ibs./= 14302 lbs.» = 5 feet, = —