Signed by Adrianus Descrolieres
Dated 1579; Antwerp
Brass; 190 mm in length (folded)
Three arms, each shaped and decorated and carrying a pair of slit sights, move on a single pivot in a decorated flat hinge. As they do so a cursor, connected to both outer arms, moves along the central arm, which is marked with two scales. One indicates the angle in degrees between the central arm and either of the outer ones, 0 to 90, 15 to 90 being divided to 10, subdivided to 5 and to 1, 20 to 90 numbered by 10. The other scale indicates the number of sides in the regular polygon generated by repeating the angle formed by the outer arms, numbered between 3 and 20.
One of the outer arms is signed 'ADescrolieres facie 1579'; the other is engraved 'Pro declinatione muri'.
On the underside of both outer arms is a table 'Pro Initijs signor[ubar]' [of the Zodiac] for 12 towns in Germany, France, the Netherlands and Italy. Pin for mounting on a staff or tripod.
See J. Bennett and S. Johnston, The Geometry of War 1500-1750 (Oxford, 1996), p. 70; and K. van Cleempoel et al, Instrumentos Cientificos del Siglo XVI: la Corte Espa?ola y la Escuela de Lovaina (Madrid, 1997), pp. 99-100, and 225-6.
Museum of the History of Science, Oxford
Inventory number 36
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