This semicircle of this graphometer is graduated to 30 minutes, and read by silvered verniers at either end of the alidade to single minutes. Benjamin Pike, Jr. (1809-1864), who was
in business in New York during the period 1843-1864, probably imported this instrument from France. New, it cost $30. The vertical sights were reconstructed at the Museum.
Ref: Benjamin Pike, Jr., Illustrated Descriptive Catalogue of Optical, Mathematical, and Philosophical Instruments (New York, 1856), pp. 64-65.