47

on a foot superficial, which is the limit of weight thebridge is capable of sustaining at the vertex.

Bamberg, Germany .

(Fir.)

c — 321.5 feet, n = 4s.^5 feet, g-= = 37.5 lbs.

/' = 7680 feet, rf = n (£'-i) = n (gg -i) = 4.75

X 22.89 = a pi’ismatick column of the same material,one square foot base, 108.73feet high, and 108.75x37«5

= 4077 lbs., and * = 1359 lbs. avoirdupois on

a foot superficial, which is the limit of weight thebridge is capable of sustaining at the vertex.

IRON BRIDGES.

Southwark, London .

(Cast English iron.)

There are eight parallel ribs and two diagonal ones2£ inches thick, the bridge is 45 feet wide, thereforethe weight sustained by each is 4.5 feet.

the weight 3317.6 must be divided by 3, then I®. = 1106 lbs.

3

on a foot superficial. It seems extraordinary that, notwithstandingthe examples of stone bridges erected by the architects of themiddle ages, notwithstanding the vaultings of ecclesiastical build-ings, and the universal practice in respect to wooden and iron bridges,that stone bridges should be erected, to the great waste of mate-rial and labour in modern times, of a uniform height of key, fromface to face, and not with ribs or arcs doubleaux.