Many navigable streams rise in the Spanish mountains; of these the Tagus has depth enough for the largest ships as high as Lisbon. Its actual course is 480 miles, but its direct line much less. In point of magnitude, however, the Spanish rivers are of inferior order, but canals have rendered them beneficial to the country. Italy is less favoured in her rivers, which only admit vessels of small burthen; those on the north are by much the most important, especially the Po and its tributaries, which by canals connect Venice and Milan with various fertile provinces of Northern Italy but whatever advantages nature has afforded to the Italian states have been improved by able engineers, both in ancient and modern times. The application of the science of hydraulics to rivers took its rise in Northern Italy, which has been carried to such perfection in some points, that China is the only country which can vie with it in the practice of irrigation. The lock on canals was in use in Lombardy as early as the 13th century, and in the end of the 15th it was applied to two canals which unite the Ticino to the Adda, by that great artist and philosopher Leonardo da Vinci: about the same time he introduced the use of the lock into France.[118] Various circumstances combine to make the British rivers more useful than many others of greater magnitude. The larger streams are not encumbered with rocks or rapids; they all run into branches of the Atlantic; the tides flow up their channels to a considerable distance; and above all, though short in their course, they end in wide estuaries and sounds, capable of containing whole navies—a circumstance that gives an importance to streams otherwise insignificant, when compared with the great rivers of either the old or new continent. The Thames, whose basin is only 5027 square miles, and whose length is but 240 miles, of which, however, 204 are navigable, spreads its influence over the remotest parts of the earth; its depth is sufficient to admit large vessels even up to London, and throughout its navigable course a continued forest of masts display the flags of every nation: its banks, which are in a state of perfect cultivation, are the seat of the highest civilization, moral and political. Local circumstances have undoubtedly been favourable to this superior development, but the earnest and energetic temperament of the Saxon races has rendered the advantages of their position available. The same may be said of other rivers in the British islands, where commercial enterprise and activity vie with that on the Thames. There are 2790 miles of canal in Britain, and, including rivers, 5430 miles of inland navigation, which, in comparison with the size of the country, is very great; it is even said that no part of England is more than 15 miles distant from water communication.