Some Early Tidal Diagrams
The earliest surviving tidal diagram is in the Catalan World Atlas, dating from 1375 and was circular in form. The Hague Atlas of c1541-1547 contained a tidal calculator which enabled tides to be calculated for as many as 81 different locations. The pocket-sized Brouscon Almanac of 1546 used chartlets rather than lists or circular diagrams. Philip Moore’s Fly from 1569 was circular in form and could calculate the tides for 32 coastal places in England and France. The tidal data in Waghenaer’s Atlas of 1583 covered both offshore and inshore tides. Thomas Hood’s 1598 chart keyed each compass point with a letter of the alphabet. These diagrams served their purpose admirably as long as the basis was the compass point rather than the hour and minute. The article compares the information provided in that Atlas with five other diagrams produced in these sources, explains its use and concludes that they were widely used by mariners until the increasing literacy of seamen made it more convenient to provide tidal information in tabular form rather than graphically.