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Ahmad B. Ali Marsil, circa 1776.
18TH CENTURY ARABIC QUADRANT FROM THE MAGHREB REGION OF NORTHWEST AFRICA
Signed along one of the sight vanes (in Arabic), "Made by the little slave of his Lord, Ahmad b'Ali Marsil, year one thousand one hundred and ninety" (1190 A.H., equivalent to 1776-77 A.D.). On one side of the brass plate there is an engraved astrolabe quadrant with data for 35 degrees North latitude. This line of latitude runs through the Maghreb Region in Northwest Africa which comprises Morocco, Algeria and Tunisia. One of the radial edges has been cut with a long indentation to provide two `sight' vanes, and a plumb-bob is attached by a string to the apex. There is also a horary quadrant for unequal hours marked at the apex. Extensive astronomical and mathematical plots are engraved on the surface including a stereographic projection of the sky with astrological symbols, various star positions and the elliptic and azimuth lines. These plots enable the quadrant's use as a computer to find rising and setting times and positions for the sun, the constellations and bright stars as well as the time of day or night, and other solutions for problems in practical astronomy. On the reverse is a sine quadrant. This has been covered by a reinforcing board and back plate with a roundel inscribed 'From the work of as-sayyid Ahmad b, Ali Marsil, may God have mercy.' This suggests that the modification was made by the original maker. At the bottom, the quadrant has an index of 0-90 for taking sights. The quadrant sight used gravity to align the plumb bob with the index reading when the celestial body was observed by eye over the top of the instrument along the sighting vanes. The string was then clamped by the observer's finger against the index, and the angle read.
Height 7.5". Width of arc 10.25".
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