What endless marvels the world offered and how much there was to know about them! One lifetime was not nearly long enough. “The rapid progress true science now makes occasions my regretting sometimes that I was born so soon,” he wrote Joseph Priestley after their countries were at peace once more. “It is impossible to imagine the height to which may be carried, in a thousand years, the power of man over matter.... O that moral science were in as fair a way of improvement that men would cease to be wolves to one another, and that human beings would at length learn what they now improperly call humanity.” He could not guess that his fervent cry would still be echoed, in one form or another, more than a hundred and seventy-five years after his death. In 1784, the King of France chose him to serve on a commission of five to investigate the work of Dr. Franz Anton Mesmer, who claimed to effect cures through “animal magnetism,”—a universal fluid which flowed to his patients from the healer, or from some object “magnetized” by the healer, such as a tree. All fashionable Paris was flocking to Mesmer’s seances; his following was enormous throughout France. With Franklin on this commission served Joseph-Ignace Guillotin (whose name would survive in the French Revolution’s chief instrument of execution) and the scientist Lavoisier (whom the guillotine would claim as a victim). After many months of study, the commission concluded that “animal magnetism” did not exist, and that Mesmer’s cures were the result of “imagination.” The importance of imagination in physical illness was as yet unrecognized. Privately Franklin commented that Mesmer’s treatments certainly did some good—at least they kept some from taking injurious drugs. On the whole the findings of the commission brought both Mesmer and mesmerism into disrepute. Indirectly the shadow of its disapproval fell on a phenomenon first discovered by a Mesmer disciple, the Marquis de Puysegur—that some persons, in a state of trance and apparently asleep, are able to obey simple commands. Hypnotism, for many years after de Puysegur’s observations, was relegated to quacks rather than physicians and scientists. In August of 1784 Thomas Jefferson arrived from America to help negotiate treaties with European and North African powers. Franklin introduced him to his French scientific friends and found in his company the same harmony as when they were both members of the Second Continental Congress. His last winter in France, Polly Hewson and her children also joined him at Passy. Mrs. Stevenson, Polly’s mother, had died in England during the war. Franklin welcomed these members of his “English family” with joy and affection.