By 1784 Franklin was seventy-eight, in poor health with a stone that made travel painful, and living at Passy outside Paris as the American minister to France. Louis XVI appointed him to head the commission on animal magnetism, and although the younger commissioners did most of the moving about, several of the decisive trials were conducted at Franklin's own house so that he could attend. The design was his kind of design: cheap, direct and aimed at a single hinge point.
A tree in the garden was magnetised by Mesmer's associate Charles Deslon, and a young man reported susceptible was led blindfolded to embrace several trees in turn; he convulsed at the wrong one. A woman was told she was being magnetised through a closed door when nobody was on the other side, and she responded; when she was magnetised without her knowledge, she did not. The commission was not testing whether patients improved, which some plainly did, but whether the claimed physical fluid existed, and it separated the two questions cleanly, which is the part that has lasted. The other commissioners were the astronomer and future mayor of Paris Jean-Sylvain Bailly, who drafted the report, the chemist Antoine Lavoisier, and the physician Joseph-Ignace Guillotin, whose name would later attach to a machine he did not invent and did not want named after him. A second commission drawn from the Royal Society of Medicine reported separately and reached a similar conclusion, with one dissenting member.