construction, but the form adopted and the material, and have given
birth to bridges of wood, brick, stone, iron, wire, and chain,--to
bridges supported by piers, to floating, suspension, and tubular
structures, many of which are among the remarkable trophies of modern
science and the noblest fruits of the arts of peace. Railways have
created an entirely new species of bridge, to enable a train to
intersect a road, to cross canals in slanting directions, to turn amid
jagged precipices, and to cross arms of the sea at a sufficient
elevation not to interfere with the passage of ships,--objects not to be
accomplished by suspension-bridges because of their oscillation, nor
girder for lack of support, the desiderata being extensive span with
rigid strength, so triumphantly realized in the tubular bridge. The day
when the great Holyrood train passed over the Strait of Menai by this
grand expedient established the superiority of this principle of
construction, and became a memorable occasion in the annals of
mechanical science, and immortalized the name of Stephenson.

We find great national significance in the history of bridges in
different countries. Their costly and substantial grandeur in Britain
accords with the solid qualities of the race, and their elegance on the
Continent with the pervasive influence of Art in Europe. It is a curious
illustration of the inferior economical and high intellectual
development of Greece, that the "Athenians waded, when their temples
were the most perfect models of architecture"; and equally an evidence
of the practical energy of the old Romans, that their stone bridges
often remain to this hour intact. Our own incomplete civilization is
manifest in the marvellous number of bridges that annually break down,
from negligent or unscientific construction; while the indomitable
enterprise of the people is no less apparent in some of the longest,
loftiest, most wonderfully constructed and sustained bridges in the
world. We have only to cross the Suspension Bridge at Niagara, or gaze
up to its aerial tracery from the river, or look forth upon wooded
ravines and down precipitous and umbrageous glens from the Erie Railway,
to feel that in this, as in all other branches of mechanical enterprise,
our nation is as boldly dexterous as culpably reckless. As an instance
of ingenuity in this sphere, the bridge which crosses the Potomac
Creek, near Washington, deserves notice. The hollow iron arches whic