On March 12, 1784, the French government ordered the Faculté de médecine to conduct an investigation of animal magnetism. It had been six years since the man who claimed to have discovered it, Franz Anton Mesmer, had established an independent medical practice in Paris, and three years since the last of several attempts to examine his methods had failed.9 This time, rather than attempt to investigate the uncooperative Mesmer, the government instructed the Faculty to examine his doctrine as practiced by his chief disciple, Charles Deslon, the personal physician to the king’s brother and one of the Faculty’s elite regent doctors.

The letter to the Faculty came from the baron de Breteuil, minister of the king’s household, who stated that the king’s order was a response to Deslon’s own request. The physician had evidently used his connections at court to obtain one last chance to vindicate his magnetic treatments. The Faculty had long since denounced animal magnetism as quackery and, despite Deslon’s status, had suspended him, threatening him with expulsion if he did not renounce Mesmer’s doctrine by August. Meanwhile, Mesmer, with whom Deslon had recently quarreled, had turned on him in public, accusing him of being a traitor, not yet initiated into the deepest mysteries of magnetism, and unqualified to operate the independent practice he had just opened.1 By March, 1784, whatever devotion Deslon may have felt toward his mentor’s code of secrecy had evaporated. The baron de Breteuil’s letter of March 12 instructed the dean of the Faculty himself, Jean-Charles-Henri Sallin, to form a three-man commission with Jean d’Arcet and Joseph-Ignace Guillotin to investigate how Deslon harnessed this insensible force in the cause of curing disease. Their report was to be submitted to the king.2

Between March 12 and the time Poissonnier wrote Franklin the present letter, much had changed in the royal commission. First it was expanded from three members to twelve, with commissioners added from the Académie des sciences (Franklin among them) and the Société royale de médecine. That configuration proving unworkable, the commission was then split in two, with separate Faculty and Society commissions sharing Franklin and his fellow members of the Academy. Later, when the work was under way, the membership would shift once again: the Society would lose the members of the Academy and continue its experiments independently. Those experiments being of little consequence, the Society’s work would be eclipsed by the conclusions of the Faculty/Academy commission.

The story of how the king came to appoint two separate commissions with the same task, both of which included Franklin and met at his residence at Passy, is not generally known. Nor has it been understood when and why the members of the Academy allied themselves exclusively with the commissioners of the Faculty of Medicine. The commissioners’ private records are gone. Negotiations among the various organizations and the government have left only partial traces, and of the surviving documents, some are undated drafts. The official reports submitted by the two commissions never mention that their members were at any time commingled. Moreover, previous historians appear to have been unaware of certain documents among Franklin’s papers, published for the first time in this volume, which contradict aspects of the standard narratives. We therefore attempt to relate this confusing history to the degree we can reconstruct it, so that our readers may understand why Poissonnier was convening the meeting that is the subject of the present letter.

Breteuil’s March 12 letter to the Faculty lay unanswered for three weeks. The fact that it had been sent, however, was soon known to the Society of Medicine, which strongly objected to being left out of the investigation. Poissonnier, Vicq d’Azyr, and Chief of Police Lenoir, who was an associate of the Society, lobbied Breteuil to broaden the commission. The Society’s argument was indisputable: advising the government on quackery and secret remedies was its explicit mandate, not that of the Faculty. Lenoir must also have discussed with Breteuil the broader issue of public safety. Mesmer’s influence had been steadily increasing, and he had become a substantial threat to the health and well-being of a credulous citizenry. His popularity was not only growing in Paris; he had recently begun to invade the purses of people throughout France and the islands by means of the Society of Harmony, which was eliciting huge fees from wealthy “students” who had been promised a copy of his doctrine, which was not yet, and never would be, printed. If the government were to receive a negative report from the Faculty, which had already declared its hostility to Mesmer and Deslon, it would have as little effect on public opinion as all previous censures. If there were to be a government-sanctioned investigation, it should be definitive, and the royal commission had to be perceived as being above any suspicion of bias. In the opinion of Lenoir, Poissonnier, and Vicq d’Azyr, the best chance of securing public confidence would be to expand the commission to include four members of the Faculty, four members of the Society, and four of the most distinguished members of the Academy of Sciences: Franklin, Bailly, Le Roy, and Lavoisier.

By the end of March, Breteuil and Lenoir appear to have come to an agreement and authorized Poissonnier to investigate the feasibility of this plan.3 On April 1, Poissonnier reported to Lenoir that Bailly, Lavoisier, and Le Roy, whom he had seen at a meeting of the Academy, had all agreed to serve as commissioners. He expected the same response from Franklin, whom he would visit either the next day or the day after. Whether the Faculty would be willing to work with the Society, if the goal were presented as the public good, was as yet unknown.4 Maloet, a member of both institutions, doubted it, but the duc de Praslin was optimistic. Poissonnier proposed that if the Faculty should refuse to join forces with the Society, each institution could work independently with the four commissioners of the Academy. Maloet had advised that in the letters of appointment to these academicians Breteuil should state that it was the physicians who had requested their counsel. Poissonnier hoped that his views conformed to those of Lenoir and Breteuil.5

They evidently did because on April 2, Breteuil sent a letter of appointment to Lavoisier, stating that the king had chosen him to examine Mesmer’s methods as practiced by Deslon. He was notably vague on who Lavoisier’s colleagues would be. Mentioning neither the Faculty nor the Society by name, he wrote that the commission would include “plusieurs autres personnes distinguées par leurs lumières et leur experience.” Following Maloet’s advice, Breteuil added that it was “les médecins eux-mêmes” who desired the collaboration.6

We assume that Bailly, Le Roy, and Franklin received similar letters of appointment around the same time. We know, at least, that Franklin’s came from Breteuil. When Temple Franklin published an edition of his grandfather’s papers, he wrote that when the king appointed a commission to investigate animal magnetism, “Dr. Franklin, at the particular request of his majesty, signified to him by a letter from the minister, consented to be one of the number.”7

On April 3, the day after Breteuil sent Lavoisier a letter of appointment, the Faculty commissioners—now four in number, Borie aving been added—collectively replied to the letter of appointment that Breteuil had sent them on March 12. Their response, as polite as the occasion required, effectively rejected both government plans: the one of March 12 (the only one they explicitly acknowledged) and the expanded one that was being implemented without their consent (to which they gave a subtle nod in their final sentence). They were honored to accept the king’s commission to examine animal magnetism, they wrote, but begged to point out that the assignment was not a straightforward one. Mesmer claimed that magnetic fluid permeated the entire universe, extending as far as the celestial bodies. There was nothing in nature, either animate or inanimate, that did not possess its energy and was not subject to its force. It therefore could be said to encompass two kinds of properties: one physical, in the general sense; the other medicinal, in that it was said to produce changes in animal constitution. As practical doctors, they were incapable of investigating the former. They requested that a preliminary study be conducted by some of those illustrious physicists whose work was so celebrated. Those scientists could determine whether this universal agent, said to be newly discovered, existed, and could identify its general properties. If it were proven to exist, then they, the doctors, would investigate its medicinal effects. This would yield a judgment “d’autant plus capable de répondre aux vues du Gouvernement et de fixer l’opinion publique.” They mentioned nothing about the Society of Medicine.8

In a letter dated only “Dimanche,” which we believe to have been written on April 4, Lassone, the president of the Society, sent an urgent message to Breteuil. He insisted on the Society’s being consulted in cases such as this, warned of the dangers of factionalism and misplaced animosity (no doubt alluding to the Faculty’s hostility toward the Society), and emphasized the advantages of a collaboration among the three bodies (i.e., the Faculty, the Society, and the Academy). Lassone also proposed the names of four commissioners from the Society.9

Breteuil was away from Versailles for almost two weeks. After his return, he settled on the compromise plan suggested by Poissonnier. On April 18 he wrote nearly identical letters to the commissioners of the Faculty and the commissioners of the Society, informing each group (without mentioning the other) that ”sur le désir que vous m’en avés témoigné par votre lettre du …,” the king had appointed four members of the Academy of Sciences—Franklin, Bailly, Le Roy, and Lavoisier (in that order)—to assist them with the examination of animal magnetism.1

The present letter from Poissonnier is the earliest piece of correspondence in Franklin’s archive that mentions any aspect of his appointment as a royal commissioner. Its chief significance lies in its indication, hitherto unrecorded, that he was, for a brief period, a member of a joint commission with the Society of Medicine. The initial meeting was held at Passy to accommodate Franklin’s limited mobility. What was discussed that day is not known, and the academicians’ role would prove to be extremely limited. Only two members of the Academy—Le Roy and Lavoisier—are known to have attended sessions at which the Society’s physicians examined patients. On May 22, the day after they signed their third procès-verbal, Lavoisier penned a declaration on behalf of both of them: since they were not doctors, their signatures could signify nothing other than that they had been present.2 That may have been the day they decided, in concert with their fellow academicians Franklin and Bailly, that their collaboration with the Society of Medicine was pointless. On that spring afternoon, all the members of the other commission, comprising academicians and members of the Faculty, gathered in Franklin’s garden and conducted the seventh of a series of systematic, rigorous experiments. With Deslon secretly pointing his rod at a tree he had just magnetized, so as to amplify the effect, his blindfolded, twelve-year-old patient, handpicked by Deslon because of the boy’s extraordinary sensitivity to animal magnetism, was led to a group of non-magnetized trees some thirty feet away, and, after hugging them, convulsed so violently that he fainted. That experiment, according to the commissioners’ report, was the one that definitively proved that animal magnetism did not exist.3

Mr. Poissonnier a Eté Chargé par mrs. Leroy, Bailly et Lavoisier de demander a Monsieur Francklin sil peut luy Convenir de les recevoir a diner vendredy prochain et s’il trouveroit bon qu’il invita aussy de Sa part les 4. Commissaires de la société Royale4 pour s’Entretenir Ensemble apres midy ou plustot a une heure avant midy du Plan qu’ils auront a Suivre pour l’Examen du Procédé de Mr Deslon.

Mr Poissonnier Saisit cette occasion de renouveller a Monsieur Francklin les assurances de son respect et de Son inviolable attachement/