In its most remote suggestion it typifies man's primal
relation to Nature, his first instinctive effort to circumvent or avail
himself of her resources; indeed, he might take his hint of a bridge
from Nature herself,--her fallen monarchs of the forest athwart a
stream, "the testimony of the rocks," the curving shores, cavern roofs,
and pendent branches, and the prismatic bow in the heavens, which a poet
well calls "a bridge to tempt the angels down."
A bridge of the simplest kind is often charmingly effective as a
landscape-accessory: there is a short plank one in a glen of the White
Mountains, which, seen through a vista of woodland, makes out the
picture so aptly that it is sketched by every artist who haunts the
region. What lines of grace are added to the night view of a great city
by the lights on the bridges! what subtile principles enter into the
building of such a bridge as the Britannia, where even the metallic
contraction of the enormous tubes is provided for by supporting them on
cannon-balls! how venerable seems the most graceful of Tuscan bridges,
when we remember it was erected in the fifteenth century,--and the
Rialto, when we think that it was designed by Michel Angelo! and how
signal an instance is it of the progressive application of a true
principle in science, that the contrivance whereby the South-Americans
bridge the gorges of their mountains, by a pendulous causeway of twisted
osiers and bamboo,--one of which, crossed by Humboldt, was a hundred and
twenty feet long,--is identical with that which sustains the magnificent
structure over the Niagara River! In a bridge the arch is triumphal,
both for practical and commemorative ends: unknown to the Greeks and
Egyptians, even the ancient Romans, it is said by modern architects, did
not appreciate its true mechanical principle, but ascribed the
marvellous strength thereof to the cement which kept intact their
semicircle.
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