Historical development and use of thousand-year-old tide-prediction tables
Abstract
Tide-prediction tables require an understanding of the relation of tide to moon and sun, as expressed by correspondence of tide heights to phases of the moon and by the lag of high tide after local meridional transit of the moon. Such tables were compiled earlier in China than elsewhere-more to satisfy the interests of sightseers of spectacular river bores than for convenience of shipping. We used the earliest extant Chinese tables of a.d. 1056 to compare ancient predictions with those from modern tide tables for the Qiantang river bore near Hangzhou. The fit of hour and height is excellent for the 10 d or so of highest (perigean) tides, but the ancient tables do not select the higher of the two daily apogean high tides during much of the rest of a month.