<P> Seleucus of Seleucia theorized around 150 B.C. that tides were caused by the Moon . The influence of the Moon on bodies of water was also mentioned in Ptolemy's Tetrabiblos . </P> <P> In De temporum ratione (The Reckoning of Time) of 725 Bede linked semidurnal tides and the phenomenon of varying tidal heights to the Moon and its phases . Bede starts by noting that the tides rise and fall 4 / 5 of an hour later each day, just as the Moon rises and sets 4 / 5 of an hour later . He goes on to emphasise that in two lunar months (59 days) the Moon circles the Earth 57 times and there are 114 tides . Bede then observes that the height of a tides varies over the month . Increasing tides are called malinae and decreasing tides ledones and that the month is divided into four parts of seven or eight days with alternating malinae and ledones . In the same passage he also notes the effect of winds to hold back tides . </P> <P> Medieval understanding of the tides was primarily based on works of Muslim astronomers, which became available through Latin translation starting from the 12th century . Abu Ma'shar (d. circa 886), in his Introductorium in astronomiam, taught that ebb and flood tides were caused by the Moon . Abu Ma'shar discussed the effects of wind and Moon's phases relative to the Sun on the tides . In the 12th century, al - Bitruji (d. circa 1204) contributed the notion that the tides were caused by the general circulation of the heavens . </P> <P> Simon Stevin in his 1608 De spiegheling der Ebbenvloet, The theory of ebb and flood, dismissed a large number of misconceptions that still existed about ebb and flood . Stevin pleaded for the idea that the attraction of the Moon was responsible for the tides and spoke in clear terms about ebb, flood, spring tide and neap tide, stressing that further research needed to be made . </P>

How many times does the tide change each day