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John Churchman (1753-1805) was an American scientist and devout Quaker whose pioneering efforts sought to solve the longstanding problem of determining longitude at sea. A self-taught surveyor and mathematician, Churchman developed a theory that used magnetic variation and the dip of the magnetic needle to calculate longitude, a proposal that drew attention both in America and Europe. He published his ideas in The Magnetic Atlas (1794), which included one of the earliest thematic maps by an American. Though ultimately unsuccessful, his work stimulated scientific discourse and earned him correspondence with prominent figures such as Thomas Jefferson, George Washington, Joseph Banks, and Condorcet. Churchman's bold ideas, despite skepticism from some quarters, represent one of the earliest American contributions to global scientific inquiry.