N. B.—It is a pity that of the inquirers who now amuse themselves with investigating these subjects, very few realize in their minds the idea of Von Reichenbach, that Od, though often exhibiting the same relations with electricity and magnetism, is yet an utterly different principle. LETTER XIV. HYPNOTISM. TRANCE-UMBRA.—Mr. Braid’s discovery—Trance-faculties manifested in the waking state—Self-induced waking clairvoyance—Conclusion. It is an advantage attending a long and patient analysis of, and cautious theorizing upon, a new subject of inquiry, that when fresh facts and principles emerge in it, instead of disturbing such solid work as I have supposed, they but enrich and strengthen it, and find, as it were, prepared for them appropriate niches. Something of this satisfaction I experience, when I have to render tardy justice to Mr. Braid’s discovery, and to give an account of the wonders realized by Dr. Darling, Mr. Lewis, and others. Or, I have observed, that trance, considered in reference to its production, has a twofold character. It presents itself either as a spontaneous seizure brought on unexpectedly by a continuance of mental or physical excitement or exhaustion; or as intentionally induced through the systematic direction by some second person, more or less cognisant what definite effects he can produce, of certain moral and physical influences upon the party intended to be wrought on. Mr. Braid has added a third causal difference to the theory of trance. He has shown that trance can be induced by the subject of it himself voluntarily, by the use of certain means, which call into operation a special principle. The effects which he obtained by these means, but which he perhaps studied too much to separate from the effects of mesmerism—these and their principle he denominated _Hypnotism_.