George Ford II (fl. 1842); surveying and nautical instruments. Frederick A. Heisely (1759-1839); clocks and mathematical instruments. George Hoff (1740-1816); clocks, surveying instruments. Thomas Mendenhall (fl. 1775); mathematical instruments and clocks. Norristown: David Rittenhouse (1732-1796), practitioner; astronomical and surveying instruments. Philadelphia: Owen Biddle (1737-1799), practitioner. Thomas Biggs (fl. 1792-1795); surveying instruments. Isaac Brokaw (fl. 1771). Benjamin Condy (fl. 1756, d. 1798); mathematical instruments and sand glasses. William Davenport (1778-1829); surveying and mathematical instruments. William Dean (?-1797); surveying and nautical instruments. George Evans (fl. 1796, d. 1798); mathematical instruments. Martin Fisher (fl. 1790); glass instruments. Joseph Gatty (fl. 1794); barometers, thermometers, and philosophical instruments. Bryan Gilmur (end of 18th century); mathematical instruments and clocks. Thomas Godfrey (1704-1749); improved reflecting backstaff. John Gould (fl. 1794); nautical, surveying, and optical instruments. Theophilus Grew (fl. 1753), practitioner. James Ham (fl. 1754-1764); mathematical instruments. James Ham, Jr. (fl. 1780); mathematical instruments. Alloysius Ketterer (fl. 1789); glass instruments. Anthony Lamb (1703-1784); mathematical instruments. Thomas Pryor (fl. 1778); mathematical instruments. Benjamin Rittenhouse (1740-c.1820); surveying and astronomical instruments. David Rittenhouse (1732-1796), practitioner; astronomical and surveying instruments. Christopher Sower [Sauer] (c. 1724-1740); mathematical instruments and clocks. Charles Taws (fl. 1795); mathematical instruments. Henry Voight (1738-1814); clocks, watches, and astronomical instruments. John Whitney (fl. 1801); mathematical and optical instruments. Thomas Whitney (fl. 1798-1823); mathematical and optical instruments. John Wood (fl. 1790); compasses. Pittsburgh: Frederick A. Heisely (1759-1839); clocks and mathematical instruments.