For my object in these Letters, generally, has been to establish principles. And the phenomena of lucidity developed in artificial trance have been only the same as, and have not been as yet made more of than, the lucidity of catalepsy. No further principle has yet emerged from their study; and my special object in this Letter has been to persuade the opponents of mesmerism to do it justice; and I think I am most likely to attain my end by not attempting to prove too much. So that nothing remains for me to do, but to observe the form in which these Letters were originally shaped, in recollection of the pleasant hours which the residence of your family at Boppard, during the winter of 1844-5, caused me, and to say finally, DEAR ARCHY, Farewell. LETTER XI. SUPPLEMENTAL.—Abnormal neuro-psychical relation—-Cautions necessary in receiving trance communications—Trance-visiting—Mesmerising at a distance, and by the will—Mesmeric diagnosis and treatment of disease—Prevision—Ultra-vital vision. The principal alterations made in “the Letters” for the present edition comprise an expansion of my account of “trances of spontaneous occurrence,” and the introduction of greater precision into our elementary conceptions of the relations of the mind and nervous system. Letters V., VI., VII., and VIII., establish that the most startling phenomena in popular superstitions, and the most wonderful performances by mesmerised persons, are but repetitions of events, the occurrence of which, as symptoms of, or as constituting, certain rare forms of nervous attacks, have been independently authenticated and put on record by physicians of credit. Letters II. and IX. exemplify the mode in which superstition has dressed up trance-phenomena; as letters III. and IV. display the contributions she has levied on sensorial illusions, the Od force, and normal exoneural psychical phenomena. Letter X. describes the method of inducing trances artificially, whereby they may be reproduced at pleasure, either in the interests of philosophical inquiry, or for important practical purposes. I dedicate the present Letter to the reconsideration of the most knotty points already handled, and to the investigation of a few other questions, the solution of which is not less difficult.