Quadrant, a Form of Sundial

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This brass horary quadrant probably dates to between 1316 and 1329. It is calibrated along the circumference by degrees with dots at the half-degrees. The circumference is marked from 280 to 360 by tens, alternating with the numbers from 270 to 190 (written backwards). A second row of numbers is marked from 100 to 180 by tens, alternating with the numbers from 90 to 10 (written backwards). The circumference is calibrated a second time with the same number markings, but the angular divisions do not line up with the first arc. The backwards numbers indicate that this instrument could function as a folded-up astrolabe. There are double scales on each leg of the quadrant. Those on the leg with the sights are for determining the sine and cosine of an angle. The scales on the leg without the sights are uneven and are for reading declination and latitude. The interior of the quadrant contains two zodiac arcs, six unnumbered hour lines which originate at the vertex, and seven other curves which originate from a point between the sights. Four stars are named and charted (Anach, Cor Leo[n]is, Os Piscis, and Cavda Scorpio[n]i[s]); their locations suggest that the maker did not understand the astronomical coordinate system of the star chart he used. There is a shadow square from the vertex, with sixteen divisions along each edge and the numbers 3, 6, 9, 12. There is a hole for a plumb line, but no plumb line.
The reverse of the quadrant contains two sights; each sight has two pinholes. There is also a central volvelle with pointer. The volvelle is unequally calibrated from 1 to 10 with varying numbers of subdivisions. The volvelle is affixed atop several circles relating to calendars. The outermost ring enables calculation of the solar cycle and is labeled: REVOLUT[I]O SOLIS: 1316: 47: 1348: 44: 1372: 49. It is calibrated in twelve sections of thirty units and marked with zodiac names. The next ring in gives data related to the last years of the lunar cycle and is labeled: REVOLUT[I]O LUNE: 1310: 69: 1329: 70: 1348.
For a modern replica, see MA.320626
National Museum of American History
Credit Line
Gift of New York University
overall: 2 cm x 16.4 cm x 19 cm; 25/32 in x 6 15/32 in x 7 15/32 in
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