Set Square Signed Pierre Le Maire

This 6-7/8" brass rule unfolds to form a set square. The outer edge of one leg has a scale for French inches (roughly 1-1/16 English inches), numbered by ones from 1 to 6. The first unit is divided into twelfths and numbered by threes from 3 to 12. The scale is marked: demy pied de Roy [half a foot of the French king]. The inner edge of this leg has a scale for English inches numbered by ones from 1 to 6. The first unit is divided into twelfths and numbered by threes from 3 to 12. The scale is marked: demy pied des Londres [half a London foot].

This leg is also marked: P^re le Maire (/) AParis. It has a pinhole for hanging a plumb bob and a rectangular hole with a rounded end (approximately 1" long) for viewing the plumb bob. The other leg has a diagonal scale, numbered vertically by ones from 1 to 10 and horizontally by twenties from 100 to 20, and a plotting scale that is numbered by hundreds from 100 to 900. Each unit is about 9/16" long. The plotting scale has eleven horizontal lines; the sixth line is marked "5" at each unit of the scale.

Pierre Le Maire (1717–1785) took over his father Jacques's workshop in the late 1730s. Large numbers of his sundials, mathematical instruments, and lodestones survive. Albert Haertlein (1895–1960), who collected this square, graduated with a bachelor's degree in civil engineering from the Massachusetts Institute of Technology in 1918. He served in the engineering corps of the U.S. Army during World War I and taught engineering at Harvard from 1919 until 1959. Haertlein was prominent in the American Society of Civil Engineers.

References: Nicholas Bion, The Construction and Principal Uses of Mathematical Instruments, trans. Edmund Stone (London: for John Senex, 1723), 12, Plate 2; Adler Planetarium, Webster Signature Database, http://historydb.adlerplanetarium.org/signatures; "News From the Classes," Technology Review 21 (1919): 645; Albert Haertlein, Papers, HUG4444, Harvard University Archives, Cambridge, Mass.

Currently not on view