THREE:Telford succeeded to Brindley, with all his boldness and skill, and with much extended experience. He executed the Ellesmere canal, which occupied a length of upwards of a hundred miles, connecting the rivers Severn, Dee, and Mersey. In the construction of this canal Telford introduced a bold, but successful, novelty. In aqueducts, instead of puddling their bottoms with clay, which was not proof against the effects of frost, he cased them with iron, and adopted the same means when he had to pass through quicksands or mere bog. Some of Telford's aqueducts were stupendous works. The Chirk aqueduct passed, at seventy feet above the river, on ten arches of forty feet span, and cost twenty thousand eight hundred and ninety-eight pounds. The aqueduct over the Dee passed at a height of one hundred and twenty-one feet above low water, and consisted of a great trough of cast-iron plates, supported on eighteen piers, and having a towing-path of cast-iron, supported on cast-iron pillars. This aqueduct took ten years in building, and cost, with its embankments, forty-seven thousand pounds. Tunnels much larger than that at Harecastle Hill were executed. That at Sapperton, on the Thames and Severn canal, executed by Mr. Whitworth, was nearly two miles and a half long, ran two hundred and fifty feet below the summit of the hill, and was large enough for boats of seventy tons burden. This was completed in 1788. These daring enterprises led to the design of a tunnel under the Thames, from Gravesend to Tilbury; but this was abandoned for want of capital. In 1804 a like attempt was made at Rotherhithe, but stopped from the same cause, and was not completed till 1843 by Sir Mark Isambard Brunel. Between 1758 and 1801 no fewer than sixty-five Acts of Parliament were passed for making or extending canals. At the end of that period canals extended over upwards of three thousand miles, and had cost upwards of thirteen millions sterling. In fact, the bulk of canal work was done by this time, though not some few works of great importance. The Leeds and Liverpool canal, begun in 1770, but not completed till 1816, opened up connection with a vast manufacturing district; and the Rochdale, Huddersfield, and Hull canals gave access for the Baltic traffic into the heart of Lancashire. The Paddington and Regent's Canals wonderfully promoted the intercourse between the interior and the metropolis. In the Highlands, the Caledonian Canal, connecting the[192] string of lakes between Inverness and the Atlantic, gave passage to ships of large burden. At the end of this reign the aggregate length of canals in England and Wales was two thousand one hundred and sixty miles; in Scotland, two hundred and twelve; in Ireland, two hundred and fifty; total, two thousand six hundred and twenty-two miles. The attention paid to roads and canals necessitated the same to bridges; and during this reign many new structures of this kind were erected, and much improvement attained in their formation. In 1776 a totally new kind of bridge was commenced at Coalbrook Dale, and completed in 1779; this was of cast-iron, having a single arch of one hundred feet span, and containing three hundred and seventy-eight and a half tons of metal. Telford greatly improved on this idea, by erecting an iron bridge over the Severn, at Buildwas, in 1796, having an arch of one hundred and thirty feet span.
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