The Art of Navigating–Navigation Instruments
Scientific progress during the Expansion Period (Early Middle Ages)
Until the beginning of the 15th century, navigation took place with land in sight. When a ship moved away, it made an estimated navigation, using the direction of the tide needle and estimating the distances navigated.
It was not easy. There were no instruments to measure speed. A study of the existing wind and current regime was needed, and adapted shipbuilding techniques to face the new distances, weather and sea conditions.
Theatro naval hidrographico: de los fluxos y refluxos y de las corrientes de los mares, estrechos, archipelagos y passages aquales del mundo: y de las diferencias de la variaciones de la aguja de marear y efectos de la luna, con los vientos generales y particulares que reynam en las quatros regiones maritimas del orbe (1688) by Francisco de Seixas y LoveraBiblioteca Central de Marinha
Analyzing tides and winds
The journeys to the south along the African coast, and especially the return to the European continent, carried out in unfavorable wind and current conditions, required greater erudition and scientific knowledge.
Vellum charts illustrating the harbors and trade routes
The old portolans, traced with estimated distances and magnetic courses, no longer serve the great oceanic navigations. The astronomical methods used to determine the position of ships at sea required the development of sciences based on mathematics and geometry.
The astronomical methods used to determine the position of ships at sea required maps in geographic coordinates, where the bathymetry and the position of coasts and islands were referenced by rigorous methods in the same coordinate system. This gave rise to modern cartography based on the mathematics and geometry. And instruments used on board ships to measure astronomical coordinates were developed.
The mariner's astrolabe (Horologium Nocturnum)
Intended to measure the height of the stars, that is, the angle with which the observer sees the star above the horizon. It was adapted in Portugal in the 15th century from ancient astronomical astrolabes to serve practical navigational interests.
Cosimo Bartoli gentil ́hvomo et academico Fiorentino, Del modo di misurare le distantie, le superficie, i corpi, le piante, le provincie, le prospettive & tutte le altre cose terrene che possono occorrere a gli huomini, Secondo le vere regole d'Euclides & de gli altri piu lodati scrittori, pág. 37 (1564) by Cosimo BartoliBiblioteca Central de Marinha
It is made up of a graduated circle suspended by a ring in the observer's hand, in the center of which an alidade, called mediclina, rotates.
The mediclina has two pinnules with holes that can be crossed by a solar ray defining the direction in which the star is, or through which it can be aimed at a star, also defining its direction.
As the circle is vertical, as it is suspended from a point and in the vertical plane that contains the star and the observer, the angle between the direction of the horizontal marked on the circle and the direction of the alidade pointed to the star can be measured on it, which is the height.
The graduation of the slice was initially marked in degrees from the horizontal to the side of the suspension, measuring the height, and later from the vertical, then measuring the complement of the heigh, and later from the vertical, then measuring the complement of the height, a coordinate called the zenith distance. Adding the meridian zenith distance of the Sun to its declination, determined the latitude of the place where the ship was.
Practical navigation or an introduction to the whole art, pág. 160 (1676) by John SellerBiblioteca Central de Marinha
The quadrant was another instrument widely used to measure the heights of the stars, namely the Polar.
It consisted of a wooden circle frame graduated along the circumference. On one of the edges it had two pinnules with which to point to the star. With the thread of a small plumb bob stuck in the center of the circumference, the height of the star in the graduated sector was read.
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