Latitude ~ Cross-staff, Quadrant

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     To identify location of a town or hill or ship on a map it is necessary to know the coordinates of latitude and longitude. Latitude is determined by measuring  the angle between the horizon and the North star. The earliest instruments for measuring this angle were the "latitude hook" of the Polynesians and the Arab "kamal."  The kamal is pictured on Portugal  1943. To my knowledge the latitude hook is not pictured on a stamp.
     The instruments for measuring latitude that are pictured on stamps are the cross-staff, the quadrant, and the astrolabe, the back staff, the sextant and the octant. The cross-staff, also known as the balestila, jackstaff or Jacob's staff was introduced in 1342 by Levi ben Gerson. It has a long graduated staff with a movable cross-member. The eye is placed at one end of the staff, and the cross-member is moved until the lower end touches the horizon and the upper end touches the star or sun.

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     The quadrant comes from about the same time. The quadrant is a quarter circle with a scale engraved on the outer edge. The star or sun is lined up on one leg of the quadrant and a weighted pointer marks the angle on the curved scale.

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