Jesse Ramsden designed the circular dividing engine that revolutionized the production of mathematical instruments with graduated arcs, and used it to produce some 1450 sextants. This example, which belongs to Brown University in Providence, Rhode Island, was made around 1790. It has a bridge-type frame, a form that Ramsden designed to minimize bending. The silvered scale is graduated every 20 minutes from -2o to +142o and read by vernier with tangent screw and magnifier to 20 second of arc.
Inside the keystone-shaped wooden box is a trade label for William Hamlin,
the instrument dealer in Providence who may have repaired the sextant at some time.
Ref: A. Stimson, "The Influence of the Royal Observatory at Greenwich upon the Design of 17th and 18th Century Angle-Measuring Instruments at Sea," Vistas in Astronomy 20 (1976): 123-130.
