Circular protractor manual#
The protractor is very similar to one depicted in the famous manual on mathematical instruments by Jean-Baptiste Delure's son-in-law, Nicolas Bion.
The base carries a maker's mark: Delure À Paris. The inner edge of the base of the protractor is slanted, and there is a notch at the origin point. Higher levels of accuracy were not reached until machine division was achieved by instrument makers such as Jesse Ramsden, who worked approximately fifty years after this protractor was manufactured. The degree lines are probably stamped rather than engraved by hand and thus represent a notable increase in workmanship over MA.326978 and MA.316861.
Protractor Signed by Delure Description This brass semicircular protractor is graduated by single degrees and marked by tens, from left to right and from right to left, from 10° to 180°. Location Currently not on view date made 18th century ID Number MA.326978 catalog number 326978 accession number 1990.0646 Data Source National Museum of American History Bennett, The Divided Circle (Oxford, 1987), 42–43. New York University donated the object in 1963. This instrument is Italian in origin and was likely made before 1800. 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. There are two holes in the limb the numbers 2 and 1 are scratched next to the holes. The protractor rests in a brass base that unfolds to form a limb, which is chipped. The instrument is decorated with floral and solar motifs. 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 scale on the "ombra retta" (or "recta") side measured tangents from 45° to 90°. The scale on the "ombra versa" side measured tangents from 0 to 45°. The horizontal side is marked (upside down): OMBRA RETTA. The vertical side is marked: OMBRA VERSA. 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 upper right side of the protractor contains a shadow square. Protractor and Shadow Square Description This brass semicircular protractor is divided by single degrees and marked by fives from 5° to 180°.
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