In the following Letters I have endeavoured to exhibit in their true light the singular natural phenomena of which old superstition and modern charlatanism in turn availed themselves—to indicate their laws, and to develop their theory. The subject is so important that I might well have approached it in a severer guise. But, slight as this performance may appear, I profess to have employed upon it the keenest and most patient efforts of reflection of which I am capable. And as to its tone at the commencement, and the prominence given to popular and trivial topics, I candidly avow that, without some such artifice, I doubt whether I should have found a publisher of repute to publish, or a circle of readers to read, my lucubrations.

It was in the winter of 1846 that the original seven Letters were written, of which the present fourteen are the third and expanded reprint. The hour had come for successfully assailing certain already shaking prejudices of the reading public. The Selbstschau of Zschokke, and the researches of Von Reichenbach, were in the hands of the literary and philosophic. The seer-gift of the former (see Letter IV.) had established the fact that one mind can enter into direct though one-sided communion with another. The undenied Od-force of the latter (see Letter I.) is evidently the same influence with that, the first crude announcement of which, by Mesmer, had scared the world into disbelief. It had now become possible to explain ghostly warnings, and popular prophecies, the wonders of natural trance, and of animal magnetism, without having recourse to a single unproven principle. I therefore made the attempt; other more efficient labourers have co-operated in the same object; and public opinion is no longer hostile to this class of inquiries.

Bad Weilbach, near Mayence,
1st August, 1851.