Description

ENORMOUS METER-LONG MATHEMATICAL SECTOR, French, c. 1820, signed “Compas (Viret)”, and “No. 9.” This major instrument measures 4-1/8″ x 20-3/4″ x 5/32″ (10 x 53 x 0.4 cm) closed, and opens to a full 39-7/16″ (100 cm). It has a three-leaf sector hinge, and closes on the central steel alignment leaf and the three alignment pins. One side is divided with a linear scale from 0 to 12 by twelfths, labeled “Pied Ancien” representing the 18th century standardized “Pied de Roy” (27.1 mm / inch), plus a double sector scale of equal parts divided from 0 to 57 by ones. The reverse has (1) a similar but unlabeled “Foot” scale of 12 inches by twelfths of an inch (at about 26.8 mm / inch), (2) a linear “Pied Métrique” scale also running from 0 to 12 by twelfths (and curiously at 27.9 mm / inch), and (3) a double sector scale of equal parts divided from 0 to 220 by ones. Condition is fine, noting numerous small nicks and scratches. This remarkable rule is housed in its softwood case with slide off lid. 

The “Pied Métrique” scale on this sector represents a fascinating period in the transition to the metric system in France. An inch of 27.9 mm gives a foot of approximately 335 mm (actually intended to be 333-1/3 mm), and thus a meter of exactly 3 feet. This was part of the “mesures usuelles” introduced by Napoleon in 1812, and finally abolished in 1839. The formal metric system had been gradually introduced into France, département by département (Paris being first), between 1795 and 1800. It was poorly understood by the populace, unpopular, and little used in local trade. As a compromise, Napoleon introduced this sort of “metric” system based on the old measures. A meter thus equaled one yard of three traditional feet, the liter was subdivided as a quart, the kilogram was specified as exactly two pounds, etc. It was a confusing journey into the eventual acceptance of the greatly simplified true metric system. The engraved word “Viret” in parentheses is something of a puzzle, but probably indicates the maker of this grand sector. A clockmaker by this name is indeed listed in Paris directories during the 1820’s, and a splendid gilt clock by him is known.