The Tonkin tides revisited

Abstract

A description of the once-daily tides of the Gulf of Tonkin in 1678 came at an awkward time for natural philosophers, before Newton's Principia had been published. Halley (in 1684) noticed the strong dependence on lunar declination (not phase), but was over-hasty in trying to reduce the varying amplitudes to a simple rule. Newton proposed a mechanism for the absence of the half-daily tide, but admitted that further observations were required to confirm it. Another explanation was made by Euler in 1740. The exact site of the original observations is obscure but is here identified through Dampier's Voyages . The subsequent history of prediction practice is briefly summarized, and attention is drawn to a recent computer model of the South China Sea that belatedly solves all the outstanding problems.