This brass semicircular protractor is divided by single degrees and marked by fives from 5° to 180°. The letter X is at the 90-degree mark. The upper right side of the protractor contains a shadow square. This is divided on both sides into sets of four units, each approximately 3/8" long and numbered from 1 to 12, for a total of 48 units on each side. The vertical side is marked: OMBRA VERSA. The horizontal side is marked (upside down): OMBRA RETTA.
The scale on the "ombra versa" side measured tangents from 0 to 45°. The scale on the "ombra retta" (or "recta") side measured tangents from 45° to 90°. The lines for degrees and on the shadow square appear to be made by hand, perhaps by placing the instrument next to a pattern. The instrument is decorated with floral and solar motifs. The protractor rests in a brass base that unfolds to form a limb, which is chipped. There are two holes in the limb; the numbers 2 and 1 are scratched next to the holes. There are four holes in the base; the numbers 3 and 1 are scratched next to the outermost holes, which align with the holes on the limb. This instrument is Italian in origin and was likely made before 1800. New York University donated the object in 1963.
Reference: J. A. Bennett, The Divided Circle (Oxford, 1987), 42–43.
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