from Norfolk in Virginia, the floating
bridge at Ticonderoga, that which spanned Stony Brook in New Jersey, and
many others, are identified with strife or stratagem: King's Bridge was
a formidable barrier to the invasion of New York by land. Indeed, from
Trenton to Lodi, military annals have few more fierce conflicts than
those wherein the bridge of the battle-ground is disputed; to cross one
is often a declaration of war, and Rubicons abound in history.

There is probably no single problem, wherein the laws of science and
mechanical skill combine, which has so won the attention and challenged
the powers of inventive minds as the construction of bridges. The
various exigencies to be met, the possible triumphs to be achieved, the
experiments as to form, material, security, and grace, have been
prolific causes of inspiration and disappointment. In this branch of
economy, the mechanic and the mathematician fairly meet; and it requires
a rare union of ability in both vocations to arrive at original results
in this sphere. To invent a bridge, through the application of a
scientific principle by a novel method, is one of those projects which
seem to fascinate philosophical minds; in few have theory and practice
been more completely tested; and the history of bridges, scientifically
written, would exhibit as remarkable conflicts of opinion, trials of
inventive skill, decision of character, genius, folly, and fame, as any
other chapter in the annals of progress. How to unite security with the
least inconvenience, permanence with availability, strength with
beauty,--how to adapt the structure to the location, climate, use, and
risks,--are questions which often invoke all the science and skill of
the architect, and which have increased in difficulty with the advance
of other resources and requisitions of civilization. Whether a bridge is
to cross a brook, a river, a strait, an inlet, an arm of the sea, a
canal, or a valley, are so many diverse contingencies which modify the
calculations and plans of the engineer. Here liability to sudden
freshets, there to overwhelming tides, now to the enormous weight of
railway-trains, and again to the corrosive influence of the elements,
must be taken into consideration; the navigation of waters, the
exigencies of war, the needs of a population, the respective uses of
viaduct, aqueduct, and roadway, have often to be included in the
problem. These considerations influence not only the method of