Of the three main styles, French sectors were the most consistent in terms of the scales with which they were marked. They were designed specifically for gunnery rather than for general applications. There were eight common scales:
- Poid des boulets, or weight of artillery shot – Although early modern cannon were not standard in size, there were different types of shot for different general types of artillery. Each type of shot had a particular volume, weight, and amount of powder. This scale helped gunners determine the required weight for a given size of shot.
- Metallic line – The alchemical symbols for certain metals (such as gold, lead, silver, copper, iron, and tin) were placed at distances from the hinge of the sector so that balls of those metals with those radii would weigh the same. The distance between any two metals gave the ratio between their weights.
- Line of solids – Used to determine the ratio between two volumes and to calculate cube roots.
- Line of chords – Used to construct angles.
- Calibre des pieces, or size of artillery shot – This scale was used to determine the size of shot, given the diameter of the cannon opening and the weight of the shot.
- Line of lines – A scale divided into equal parts used as the base scale for taking measurements that are transferred to other scales with a pair of dividers. For example, open the dividers to a length on the line of lines and then pivot the dividers and open the sector so that the lifted point of the dividers falls on the other leg of the sector.
- Line of planes – Used to determine the ratio between two areas and to calculate square roots.
- Tetragonic line – Points placed from the hinge to represent the sides of regular polygons with the same area, from the triangle to a 13-sided polygon. Used to set up proportions to determine the areas of regular polygons with other side lengths.
"Sectors - French Style" showing 1 items.
- The arms of this brass instrument have straight edges, but the hinge is decorated with a flower. One side has double scales of chords, running from 10 to 180; of solids, running from 1 to 64; and for the specific weights of five metals, marked with their symbols. On one arm, the outer edge has a scale that runs from 4 to 24 and is labeled "Poids des Boulets." The sector is marked: Lennel à La (/) Sphére à Paris.
- The other side has double scales for equal parts, running from 10 to 200; for architectural drawings, running from 1 to 64; and for the lengths of the sides of inscribed regular polygons, from 12 sides to three sides. On one arm, the outer edge has a scale running from 4 to 24 and labeled "Calibre des Pieces."
- In 1774, Louis-Pierre-Florimond Lennel took over the Paris workshop operated by his teacher, Jacques Canivet, who previously had succeeded his uncle, the famous instrument maker Claude Langlois. All three men supplied telescopes to French astronomers. By 1781, Lennel called himself the official maker for France's king and the navy. He died by 1784 and was succeeded by his widow.
- References: Maya Hambly, Drawing Instruments, 1580–1980 (London: Sotheby's Publications, 1988), 28; Harriet Wynter and Anthony Turner, Scientific Instruments (New York: Charles Scribner's Sons, 1975), 158; Adler Planetarium, Webster Signature Database, http://historydb.adlerplanetarium.org/signatures/.
- Currently not on view
- date made
- Lennel, Louis-Pierre Florimond
- ID Number
- catalog number
- accession number
- Data Source
- National Museum of American History, Kenneth E. Behring Center