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. In Caesar's "Commentaries," the bridge transit and vigilance form no small part of military tactics,--boats and baskets serving the same purpose in ancient and modern warfare. The Church of old originated and consecrated bridges; religion, royalty, and art celebrate their advent; the opening of Waterloo Bridge is the subject of one of the best pictures of a modern English painter; and Cockney visitors to the peerless Bridge of Telford still ask the guide where the Queen stood at its inauguration. But it is when we turn from the historical and scientific to the familiar and personal that we realize the spontaneous interest attached to a bridge. It is as a feature of our native landscape, the goal of habitual excursions, the rendezvous, the observatory, the favorite haunt or transit, that it wins the gaze and the heart. There the musing angler sits content; there the echoes of the horse's hoofs rouse to expectancy the dozing traveller; there the glad lover dreams, and the despairing wretch seeks a watery grave, and the song of the poet finds a response in the universal heart,-- "How often, oh, how often, In the days that have gone by, Have I stood on that bridge at midnight, And gazed on the wave and sky!"