The theory on which he based his jetties was really extremely simple. He said that, other things being equal, the amount of sediment which a river can carry is in direct proportion to its velocity. When, for any reason, the current becomes slower at any special place, it drops part of its burden of sediment at that place, and when it becomes faster again it picks up more. Now, one thing that makes a river slower is an increase of its width, because then there is more frictional surface; and contrariwise, one of the things that make it faster is a narrowing of its width. Narrow the Mississippi then, at its mouth, said Eads, and it will become swifter there, and consequently it will remove its soft bottom by picking up the sediment (of which it will then hold much more), and by carrying it out to the gulf, to be lost in deep water and swept away by currents; and thus, he said, you will have your deep channel. In other words, if you give the river some assistance by keeping its current together, it will do all the necessary labor and scour out its own bottom. Today, since this theory has been proved, it seems as simple as A B C. And it is almost impossible to believe what opposition it then aroused. People were not only set on blocking the undertaking, but they were actually ignorant enough to deny that the velocity of water had any connection with its sediment-carrying power. Even if the narrowing process should happen to give a channel through the present bar, they said, a new one would presently form beyond, and so the jetties would have to be extended every year.