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taking the largest class of ships navigating the canal, and capable of being closed on occasions of necessity, the several channels uniting at a little distance north of the basin.
In the second place, I would secure the structure of the canal in weak ground by solid ribs of masonry, constructed at proper intervals. These ribs of masonry, corresponding in form and size to the section of the canal, and having the upper surface of the bottom placed correctly to the level assigned by the declivity of the canal, would serve as accurate gauges to the water passing, and would preserve the bottom from any under wear: thus, if we suppose these ribs of masonry, placed a mile apart, and with a regular difference of level of 4 731 inches between each adjoining pair, the bed of the intermediate portion would be preserved upon the regular incline, since, the extremities being secured from erosion, it is not to be supposed that a straight and equable stream, with so gentle a fall, would have any tendency to wear its bed lower than the gauged sections of masonry.
We have now to consider what would be the velocity of the current due to such a navigable channel of running water.
It may be observed, that large rivers flow with greater rapidity than might be expected from the slightness of their declivity; and that when great bodies of water have obtained a considerable impetus, they continue to flow for a great distance over a flat or level surface. The Great Maranon, it is said, has only a descent of 10^ feet in the last 200 leagues of its course. The Loire, between Briare and Orleans, falls only 1 foot in 13,596 feet; and the rapid Rhine falls but 2 feet in a mile between Strasburg and Schenckenschantz; and where the Po falls 6 inches per mile, its velocity amounts to 3^ miles per hour.
The velocity of a stream of water depending conjointly on the fall or declivity of the surface and on the form and