Coenraad Metz (Danzig 1643-65, Amsterdam 1665-1711).
Small silver protractor and a small brass protractor, both unsigned, late 17th to early 18th century.
Fig.1. Magnificent little silver half-circle protractor, graduated into half-degrees intervals, and marked by 10s moving in both directions from 0 to 180. The inner scale, indicated in
Latin Anguli Poliigonorem Regular, is marked with positions for regular polygons from 3 to 12 sides. The unusual spelling of Poliigonorem is also engraved on a Holland
Circle by Coenraad Metz at the now defunct Time Museum in Rockford, Ill. Base 85mm, 55mm from the base to the apex.
Fig.2. Small brass half-circle protractor graduated in degrees with hand-engraved numbering. The inner scale, indicated in Latin Anguli Polygonorem Regular, is marked with positions for regular polygons of between 3 and 12 sides. Base measures 68mm, height 45mm.
Fig. 3. Holland Circle, unsigned, possibly by Metz, uncertain dating 1650-1750. Compass needle and compass glass is missing. Diameter is 154mm.
In the late 16th century, a Dutch scholar and instrument maker named Gemma Frisius suggested that a good surveying instrument could be made by attaching a magnetic compass to the back of an astrolabe. Building on this idea, Jan Dou designed an instrument with two pairs of fixed sights attached to a graduated circle, and another pair of sights attached to either end of a movable alidade. Dou published an account of this instrument in Dutch in 1612, and the form became popular with surveyors in the Netherlands. The name Holland Circle was coined in the 19th century. The Holland Circle is similar to but easily distinguishable from the common theodolite.
NOTES / REFERENCES
1. The silver protractor is similar to the protractor attributed to Coenraad Metz in Museum Boerhaave.
2. The brass protractor is similar to the one in a set of drawing instruments attributed to Conraad Metz at the Maritime Museum of Friesland.
4. DAUMAS, M. 1972. Scientific Instruments of the 17th & 18th Centuries and their Makers. p. 87, 249.
"...Coenraad Metz (the elder) was born in Danzig in 1643 and settles in Amsterdam in 1665. He worked for de Volder and made a sextant on the model of that of Tycho Brahe for the sum of 1,050 florins, as well as mathematical instruments for the observatory in Leiden. He is well known and highly esteemed by Dutch scolars. He died in about 1711, his workshop being taken over several years later by his grandson, Coenraad Fibus Metz."
5. POULS, H.C. 2004: De landmeter Jan Pietersz. Dou en de Hollandse Cirkel, Delft. p. 71.
6. VAN CITTERT, P.H.,1954; Astrolabes, a critical description of the astrolabes and quadrants in care of the Utrecht University Museum, Leiden. plates XXII and XXIII.
7. ZUIDERVAART, Huib J. 2007; Telescopes from Leiden Observatory and other Collections 1656-1859 A Descriptive Catalogue.
8. POULS, H.C.; Een nuttig en profijtelijk boekje voor alle geografen. Gemma Frisius. Nederlandse Commisiie voor Geodesie - Stichting De Hollandse Cirkel, 1999.