fifty acres of land, and sixty tons of iron bolts, costing only
$140,000, and built in the short time of eighteen months. This
structure, if replaced by an earth embankment, would cost half a
million of dollars, and could not be built in less than five years
by the ordinary mode of proceeding.[2]

Further, the interest, for so long a time, on the large amount of
money required to build the embankment, at the high rate of railroad
interest, would nearly, if not quite, suffice to build the wooden
structure.

Again, our wooden bridges of the average span cost about thirty-five
dollars per lineal foot. Let us compare this with the cost of iron
bridges, on the English tubular plan, the spans being the same, and
the piers, therefore, left out of the comparison.

Suppose that a road has in all one mile in length of bridges. Making
due allowance for the difference in value of labor in England and
America, the cost per lineal foot of the iron tubular bridges could
not be less (for the average span of 150 feet) than three hundred
dollars.

5280 feet by $35 is $184,800.00
5280 feet by 300 is $1,584,000.00
The six per cent. interest on the first is $11,088.00
The six per cent. interest on the second is $95,040.00
And the difference is $83,952.00

or nearly enough to rebuild the wooden bridges once in two years;
and ten years is the shortest time that a good wooden bridge should