Photo by David Friend Productions, San Diego, California
18th C AMERICAN SURVEYOR'S MAHOGANY SEMI-CIRCUMFERENTOR
06-003. American, 4th quarter 18th century, unsigned. Made of mahogany, 11 1/2" x 6 1/8" x 1 1/2",
with a 10 1/2" diameter brass protractor mounted on top and a 4 3/8" x 1 3/8" trough compass inset
in the center of the protractor. The trough compass needle is 4" long; there is an brass plate in
the bottom of the trough with a ruled line in the center; and the original compass glass is sealed
in with a brass frame. The sighting mechanism mounts on a screw with the original nut in the center
of the base of the protractor, with 3 3/4" tall sight vanes on each end and cutouts to read angles
on the protractor. The 4 1/4" x 3" x 1 1/4" mahogany staff mounting bracket is in the center of the
base. This attractive early American surveying instrument is in very good overall condition, with
original patina on the brass and no age cracks in the wood. See page 69 and Plate XXXII in M.V.
Brewington's "The Peabody Collection of Navigating Instruments" for a picture and description of a
very similar American semi-circumferentor (dated circa 1730).
