![]() ![]() However a scientific explanation for the tidal phenomenon had to wait for Sir Isaac Newton and his universal theory of gravitation which was published in 1687. The Navigator, particularly in estuarine and coastal waters and the approaches to harbours. This is very important, as the Navy would not be able to defend our waters without accurate charts. The Hydrographic Surveyor in order to reduce soundings to a common datum. Why do we need tidal predictions? Knowledge of the times and heights of tides and the speed and direction of tidal streams is important to a variety of people. This can add additional complications to an already complicated situation. In addition, we must also look at non-gravitational factors (eg seasonal, wind) that frequently have a large influence on the behaviour of the sea level. This is due to coastal topography and the shape of the ocean bottom which plays a major role in determining the tidal patterns around the country. It has a full spectrum of tidal regimes, and a tidal range varying from 1m to over 10m. Australia is however very complex from a tidal point of view. South Africa has a relatively simple tidal system with semi-diurnal tides and a relatively small tidal range. Details of the tides at any given place are governed by the responses of the ocean to the gravitational forces. Thus the gravitational theory became established as the basis for all tidal science. ![]() He also showed why there are two tides for each lunar transit, the reason why spring and neap tides occurred, why diurnal tides are largest when the moon was furthest from the plane of the equator and why the equinoxial tides are larger in general than those at the solstices. He described in his “ Principia Mathematica ” how the tides arose from the gravitational attraction of the moon and the sun on the earth. In the late 10 th century, the Arabs had already begun to relate the timing of the tides to the cycles of the moon. One ascribed the tides to the breathing cycle of a giant whale. In the beginning tides were explained by all sorts of legends. It was this ignorance of tides that led to the loss of Caesar’s war galleys on the English shores, he failed to pull them up high enough to avoid the returning tide. Tides are very often neglected or taken for granted, “they are just the sea advancing and retreating once or twice a day.” The Ancient Greeks and Romans weren’t particularly concerned with the tides at all, since in the Mediterranean they are almost imperceptible. Tides: The periodic vertical movement of water on the Earth’s Surface ![]()
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