I shall endeavour to convey, in a few words, a general idea of the principles on which this grand undertaking has been carried on. All the rivers of note in China fall from the high lands of Tartary, which lie to the northward of Thibet, crossing the plains of this empire in their descent to the sea from west to east. The inland navigation being carried from north to south cuts these rivers at right angles, the smaller streams of which terminating in it afford a constant supply of water; and the three great rivers, the _Eu-ho_ to the north, the _Yellow River_ towards the middle, and the _Yang-tse-kiang_ to the south, intersecting the canal, carry off the superfluous water to the sea. The former, therefore, are the _feeders_, and the latter the _dischargers_, of the great trunk of the canal. A number of difficulties must have arisen in accommodating the general level of the canal to the several levels of the feeding streams; for notwithstanding all the favourable circumstances of the face of the country, it has been found necessary in many places to cut down to the depth of sixty or seventy feet below the surface; and, in others, to raise mounds of earth upon lakes and swamps and marshy grounds, of such a length and magnitude that nothing short of the absolute command over multitudes could have accomplished an undertaking, whose immensity is only exceeded by the great wall. These gigantic embankments are sometimes carried through lakes of several miles in diameter, between which the water is forced up to a height considerably above that of the lake; and in such situations we sometimes observed this enormous aqueduct gliding along at the rate of three miles an hour. Few parts of it are level: in some places it has little or no current; one day we had it setting to the southward at the rate of one, two, or three miles an hour, the next to the northward, and frequently on the same day we found it stationary, and running in opposite directions. This balancing of the level was effected by flood-gates thrown across at certain distances to elevate or depress the height of the water a few inches, as might appear to be necessary; and these stoppages are simply planks sliding in grooves, that are cut into the sides of two stone abutments, which in these places contract the canal to the width of about thirty feet. There is not a lock nor, except these, a single interruption to a continued navigation of six hundred miles. The most remarkable parts of this extraordinary work will be noticed in a following chapter, descriptive of our journey through the empire.