Benjamin Franklin

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.

The commission concluded that no evidence supported the existence of a magnetic fluid and that the effects observed were produced by imagination, by imitation among patients treated in groups, and by touch. Read now, the report is remarkable less for its verdict than for its method, and it is routinely cited in the history of clinical trials as an early and unusually clean use of two techniques that would not be named for another century and a half. The first is blinding: the subject was prevented from knowing whether the treatment was being administered, which is the only way to separate a treatment from the belief that it is being given. The second is a genuine control condition, since sham magnetisation was applied and compared against the real thing rather than merely reasoned about.

Franklin himself drew a conclusion the report only implies, remarking that some of the cures were real even if the theory was nonsense, and wondering in correspondence whether the imagination might be turned to account deliberately. That is close to the modern research question about placebo response, arrived at two centuries early and then dropped. The report also had a political edge, since Mesmer's clientele overlapped with fashionable Paris, and its authors were aware they were puncturing a craze as well as a theory.