The causes for many of the inequalities in the tidal elements observed
at different places have not yet been satisfactorily explained. The
phenomena are dependent on many purely terrestrial conditions. While we
are able to ascertain with tolerable accuracy from certain constants,
derived from observation, the times and heights of the tides, the
problem to compute theoretically the tides of an ideal ocean of known
depth and configuration remains still unsolved. According to Ferrel our
present knowledge of tidal phenomena is comparable to that possessed
2,000 years ago of the science of astronomy.