In May 1782, Barton, who had a reputation for his knowledge of heraldry, was consulted by the Third Great Seal Committee to contribute to the design of a national coat-of-arms for the United States. He drafted what he called Device for an Armorial Atchievement for the United States of North America, blazoned agreeably to the Laws of Heraldry. He introduced an eagle with wings "displayed", an element that Secretary of the Continental CongressCharles Thomson greatly emphasized in the final proposal. The new design for the reverse of the seal incorporated the Eye of Providence atop a pyramid of thirteen steps. This combined the influence of Pierre Eugene du Simitiere, who had included the Eye of Providence in his designs for the First Great Seal Committee, with that of Francis Hopkinson, who had consulted for the Second Great Seal Committee, and who had included a similar pyramid in his 1778 design for the Continental Currency. On June 20, the design, as amended and expanded by Thomson, was adopted by the Continental Congress. On the subject of heraldry, Barton wrote a 1788 letter to General George Washington: In 1789, Washington nominated Barton as a Judge of the Western Territory. Barton declined the appointment.
Later publications
In 1787, Barton was elected to Benjamin Franklin's American Philosophical Society. In 1791, his uncle, David Rittenhouse, became the Society's second president, after Franklin's death in 1790. By 1800, William moved back to Lancaster. In 1802, he published a lengthy treatise entitled A Dissertation on the Freedom of Navigation and Maritime Commerce, and such Rights of States Relative Thereto, as are founded on the Law of Nations. He dedicated this work to Thomas Jefferson, who was the President of the United States at the time, as well as the president of the American Philosophical Society. In 1813, he published Memoirs of the life of David Rittenhouse. Jefferson had already subscribed for six copies. Former President John Adams, who received a copy of the book from Barton, wrote in an 1814 letter to Jefferson: Barton was elected a member of the American Antiquarian Society in 1814. Barton proposed an ambitious series of biographies, to be published in three volumes a year under the title, Select American Biography, Or, An Account of the Lives of Persons, Connected by Nativity, or Otherwise With the History of North America, Since the First Discovery of that Country. He described his intention for this project: He died in Lancaster on October 21, 1817 before the project could be realized.