Henry's son Thomas Voight worked as a clockmaker on North Seventh Street in Philadelphia around 1811. He was the maker of a tall case clock, ordered by Thomas Jefferson, that Jefferson's daughter presented in 1826 to her father's physician, Dr. Dunglison, for settlement of medical services.[66] There were several instrument makers in provincial Pennsylvania, but the majority of such craftsmen worked in Philadelphia. Dr. Christopher Witt (1675-1765), an emigrant from England, worked in Germantown from about 1710 to 1765. He was well known locally as a medical doctor, scientist, "hexmeister", clockmaker, and teacher. It is traditionally claimed that he produced mathematical instruments in addition to timepieces. He described the great comet of 1743 and built his own 8-foot telescope. One of his apprentices may have been Christopher Sower (1693-1740), of Germantown and Philadelphia, who achieved renown as a doctor, farmer, author, printer, papermaker, and clockmaker. He also produced mathematical instruments.[67] George Wall, Jr., of Bucks County, was the author of a pamphlet on the subject of "a newly invented Surveying Instrument, called the Trigonometer." The instrument was described and illustrated in the pamphlet, which was published in Philadelphia in 1788. Washington's own copy, bearing the inscription "To the President of the United States from the Author" is in the collection of the Boston Athenaeum. George Ford of Lancaster maintained a shop on West King Street, probably from the end of the 18th century until 1840. There he made tall case and other clocks, surveying compasses, and other instruments for the retail trade. However, he "did not push the business of Watchmaking and Clockmaking so hard, for the manufacture of nautical instruments and surveyors instruments was a more important part of his business."[68] Upon his death in 1842 he was succeeded by his son George Ford II. Thomas Mendenhall repaired clocks and mathematical instruments in a shop on King and Queen Streets in the borough of Lancaster in 1775.[69] John Wood of Philadelphia was a wholesale supplier of parts for clockmakers and watchmakers. According to a notice in the May 7, 1790, issue of _Pennsylvania Packet_, he had "pocket compasses, steel magnets, Surveying compass needles, surveyors chains, etc." Since no mention was made of making or mending instruments, it is probable that Wood was merely importer and wholesaler. Another instrument maker of Philadelphia about whom little is known is Bryan Gilmur, who worked at the close of the 18th century making instruments and, possibly, clocks.[70]