Atlantic Monthly | Page 6

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 last.
The reader may wonder why such structures as the bridge over the
Susquehanna at Columbia, which consists of twenty-nine arches, each

two hundred feet span, the whole water-way being a mile long, and
many other bridges spanning large rivers, and having an imposing
appearance, are not referred to in this place. The reason is this: large
bridges are by no means always great bridges; nor do they require, as
some seem to think, skill proportioned to their length. There are many
structures of this kind in America, of twenty, twenty-five, or thirty
spans, where the same mechanical blunders are repeated over and over
again in each span; so that the longer they are and the more they cost,
the worse they are. It does not follow, because newspapers say,
"magnificent bridge," "two million feet of timber," "eighty or one
hundred tons of iron," "cost half a million," that there is any merit
about either the bridge or its builder; as one span is, so is the whole;
and a bridge fifty feet long, and costing only a few hundreds, may show
more engineering skill than the largest and most costly viaducts in
America. Few bridges require more knowledge of mechanics and of
materials than Mr. Haupt's little "trussed girders" on the Pennsylvania
Central Road,--consisting of a single piece of timber, trussed with a
single rod, under each rail of the track.
Again, as regards American iron bridges, the same result is found to a
great extent. Thus, Mr. Roebling's Niagara Railroad Suspension-Bridge
cost four hundred thousand dollars, while a boiler-plate iron bridge
upon the tubular system would cost for the same span about four
million dollars, even if it were practicable to raise a tubular bridge in
one piece over Niagara River at the site of the Suspension Bridge.
Strength and durability, with the utmost economy, seem to have been
attained by Mr. Wendel Bollman, superintendent of the
road-department of the Baltimore and Ohio Railroad,--the minute
details of construction being so skilfully arranged, that changes of
temperature, oftentimes so fatal to bridges of metal, have no hurtful
effect whatever. And here, again, is seen the distinctive American
feature of adaptation or accommodation, even in the smallest detail. Mr.
Bollman does not get savage and say, "Messieurs Heat and Cold, I can
get iron enough out of the Alleghanies to resist all the power you can
bring against me!" --but only observes, "Go on, Heat and Cold! I am
not going to deal directly with you, but indirectly, by means of an agent
which will render harmless your most violent efforts!"--or, in other

words, he interposes a short link of iron between the principal members
of his bridge, which absorbs entirely all undue strains.
It is not to be supposed from what has preceded, that the American
engineer does not know how to spend money, because he gets along
with so little, and accomplishes so much; when occasion requires, he is
lavish of his dollars, and sees no longer expense, but only the object to
be accomplished. Witness, for example, the Kingwood Tunnel, on the
Baltimore and Ohio Railroad, where for a great distance the lining or
protecting arching inside is of heavy ribs of cast iron, --making the cost
of that mile of road embracing the tunnel about a million of dollars.
Nor will the traveller who observes the construction of the New York
and Erie Railroad up the Delaware Valley, of the Pennsylvania Central
down the west slopes of the Alleghanies, or of the Baltimore and Ohio
down the slopes of Cheat River, think for a moment that the American
engineer grudges money where it is really needed.