View of Thomas Pope's Proposed Cantilever (1810)
The most notable invention of latter days in bridge construction is that of the cantilever bridge, which is a system devised to dispense with staging, or false works, where from the great depth, or the swift current, of the river, this would be difficult, or, as in the case of the Niagara River, impossible to make. The first design of which we have any record was that of a bridge planned by Thomas Pope, a ship carpenter of New York, who, in 1810, published a book giving his designs for an arched bridge of timber across the North River at Castle Point, of 2,400 feet span. Mr. Pope called this an arch, but his description clearly shows it to have been what we now call a cantilever. As was the fashion of the day, he indulged in a poetical description: "Like half a Rainbow rising on yon shore, While its twin partner spans the semi o'er, And makes a perfect whole that need not part Till time has furnish'd us a nobler art."
Kinzua Viaduct; Erie Railway.
Valleys and ravines are now crossed by viaducts of iron and steel, of which the Kinzua viaduct, illustrated here, is an example. A branch line from the Erie, connecting that system with valuable coal-fields, strikes the valley of the Kinzua, a small creek, about 15 miles southwest of Bradford, Pa. At the point suitable for crossing, this ravine is about half a mile wide and over 300 feet deep. At first it was proposed to run down and cross the creek at a low level by some of the devices heretofore illustrated in this article. But finally the engineering firm of Clarke, Reeves & Co. agreed to build the viaduct, shown above, for a much less sum than any other method of crossing would have cost. This viaduct was built in four months. It is 305 feet high and about 2,400 feet long. The skeleton piers were first erected by means of their own posts, and afterward the girders were placed by means of a travelling scaffold on the top, projecting over about 80 feet. No staging of any kind was used, nor even ladders, as the men climbed up the diagonal rods of the piers, as a cat will run up a tree.
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