"Before entering upon either of the theories explaining the Tides, we must allude to their inadequacy, perhaps not to the explanation of the facts already observed, but certainly to the prediction of new ones. This inadequacy does not appear to arise from any defect in the principles upon which the theory is based,... but from the extreme difficulty of investigating mathematically the motions of fluids under all the various circumstances in which the waters of the sea and of rivers are found. For the problem of the Tides, it is evident, is essentially one of the motion of fluids. Yet so difficult are the investigations of motion that, till the time of Laplace, no good attempt was made to determine, by theory, the laws of the Tides, except on the supposition that the water was at -rest. Since that time theories of motion have been applied..."