45* Letters and Papers

That tlils is not mere theory, bat conformable to fact, weknow by our long rivers in America, The Delaware, onwhich Philadelphia stands, is in this particular similar tothe canal I have supposed of one wave: For when it ishigh water at the Capes or mouth of the river, it is alsohigh water at Philadelphia, which stands about 140 milesfrom the sea; and there is at the fame time a low water inthe middle between the two high waters; where, when itcomes to be high water, it is at the fame time low water atthe Capes and at Philadelphia, And the longer rivers have,some a wave and half, some two, three, or four waves, ac-cording to their length.—In the shorter rivers of this island,one may fee the fame thing in part: for instance, it is highwater at Gravefend an hour before it is high water at LyndonBridge i and 20 miles below Grave fend an hour before it ishigh water at Gravesend Therefore at the time of high 1 'water at Gravejend the top of the ware is there, and thewater is then not fo high by some feet where the top of thewave was an hour before, or where it will be an hour after,as it is just then at Gravesend,

Now we are not to suppose, that because the swell or topof the wave runs at the rate of 20 miles an hour, that there-fore the current or water itself of which the wave is com-posed, runs at that rate. Far from it. To conceive thismotion of a wave, make a small experiment or two. Fasten■one end of a cord in a window near the top of a house, andlet the other end come down to theground; take this end in

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