It was in a mood of irritable skepticism that the Scottish surgeon James Braid attended a public demonstration of Animal Magnetism—in which people were said to fall into trances—on the night of November 13, 1841. From everything he had read and heard about the trances that occurred at the bidding of the operator—the person who induced the trances—he reports that he was “fully inclined to join with those who considered the whole thing to be a system of collusion and delusion, or an excited imagination, sympathy, or imitation.” After observing the demonstration, he considered that the trances were quite genuine, but at the same time he felt satisfied “that they were not dependent on any special agency or emanation passing from the body of the operator to that of the patient as animal magnetizers allege.” He returned to the demonstration when it was repeated by popular demand a week later, and on this occasion he felt that he had identified the cause of these mysteriously punctual onsets of “nervous sleep.” He was to devote the last eighteen years of his life to the topic, and under the proprietary title of Hypnotism he explained and redescribed the process in terms which would have been unrecognizable to its eighteenth-century discoverer, Franz Anton Mesmer.
Mesmer was born in the lakeside town of Constanz in 1734, and after receiving a philosophical education from the local Jesuits he studied medicine at the University of Vienna and qualified as a physician in 1767 with the publication of an MD thesis on the influence of celestial gravity on human physiology. He argued that the rotation of the heavenly bodies exerted gravitational influence on human physiology analogous to the tidal effect of the moon upon the ocean and that this accounted for the periodic incidence of various diseases.
To explain the transmission of this influence he invoked the existence of an immaterial substance, a weightless or so-called imponderable fluid, whose universal distribution guaranteed action at a distance. The notion of such an ethereal medium can be traced back to Greek antiquity and under various titles—ether, spiritus, pneuma, etc.—it figures as a recurrent theme in European scientific thought. It played a prominent part in the long tradition of Neoplatonism, and in all probability it was under the influence of this somewhat occult tradition that Isaac Newton cautiously invoked the existence of “a subtle spirit which pervades and lies hid in all gross bodies; by the force and action of which spirit, particles of bodies attract one another.” The medium is frequently mentioned in Newtonian unpublished correspondence, and there are several references to it both in the Principia and in the more widely read Optics.
Although Newton stressed it was no more than a hypothesis, some of the commentators who sought to explain and publicize his work appear to have taken the existence of the Newtonian ether quite literally,…
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