<P> Prior to 1577, no method of judging the ship's speed was mentioned that was more advanced than observing the size of the vessel's bow wave or the passage of sea foam or various floating objects . In 1577, a more advanced technique was mentioned: the chip log . In 1578, a patent was registered for a device that would judge the ship's speed by counting the revolutions of a wheel mounted below the ship's waterline . </P> <P> Accurate time - keeping is necessary for the determination of longitude . As early as 1530, precursors to modern techniques were being explored . However, the most accurate clocks available to these early navigators were water clocks and sand clocks, such as hourglass . Hourglasses were still in use by the Royal Navy of Britain until 1839 for the timing of watches . </P> <P> Continuous accumulation of navigational data, along with increased exploration and trade, led to increased production of volumes through the Middle Ages . "Routiers" were produced in France about 1500; the English referred to them as "rutters ." In 1584 Lucas Waghenaer published the Spieghel der Zeevaerdt (The Mariner's Mirror), which became the model for such publications for several generations of navigators . They were known as "Waggoners" by most sailors . </P> <P> In 1537, Pedro Nunes published his Tratado da Sphera . In this book he included two original treatises about questions of navigation . For the first time the subject was approached using mathematical tools . This publication gave rise to a new scientific discipline: "theoretical or scientific navigation". </P>

Who established a school in portugal to help sea captains get better at navigation