Guppy's flight, who glories in being so completely unfettered by scientific prejudices as to be free to swallow anything, however preposterous and impossible in the estimation of scientific men, that his belief in "spiritual" agencies may lead him to expect as probable.
If time permitted, it would be my endeavor to show you, by an historical examination of these marvels, that there has been a long succession of epidemic delusions, the form of which has changed from time to time, while their essential nature has remained the same throughout; and that the condition which underlies them all is the subjection of the mind to a dominant idea. There is a constitutional tendency in many minds to be seized by some strange notion which takes entire possession of them; so that all the actions of the individual thus "possessed" are results of its operation. This notion may be of a nature purely intellectual, or it may be one that strongly interests the feelings. It may be confined to a small group of individuals, or it may spread through vast multitudes. Such delusions are most tyrannous and most liable to spread when connected with religious enthusiasm: as we see in the dancing and flagellant manias of the middle ages; the supposed demoniacal possession that afterward became common in the nunneries of France and Germany; the ecstatic revelations of Catholic and Protestant visionaries; the strange performances of the Convulsionnaires of St.-Médard, which have been since almost paralleled at Methodist "revivals" and camp-meetings; the preaching epidemic of Lutheran Sweden, and many other outbreaks of a nature more or less similar. But it is characteristic of some of the later forms of these epidemic delusions that they have connected themselves rather with science than with religion. In fact, just as the performances of Eastern magi took the strongest hold of the Roman mind when its faith in its old religious beliefs was shaken to its foundations, so did the grandiose pretensions of Mesmer—who claimed the discovery of a new force in Nature, as universal as gravitation, and more mysterious in its effects than electricity and magnetism—find the most ready welcome among skeptical votaries of novelty who paved the way for the French Revolution; and this pseudo-scientific idea gave the general direction to the doctrines taught by Mesmer's successors, until, in the supposed "spiritualistic" manifestations, a recurrence to the religious form took place, which, I think, may be mainly traced to the emotional longing for some assurance of the continued existence of departed friends, and hence of our own future existence, which the intellectual loosening of time-honored beliefs as to the immortality of the soul has brought into doubt with many.
I must limit myself, however, to this later phase of the history, and shall endeavor to show you how completely the extravagant pretensions of mesmerism and odylism have been disproved by scientific investigation; all that is genuine in their phenomena having been accounted for by well-ascertained physiological principles; while the