throw a flood of light upon the general subject of Psychology. This vast array of facts, thus accumulated and verified, and awaiting scientific classification and analysis, would seem to justify at least a tentative effort to apply to them the processes of induction, to the end that the fundamental law of psychic phenomena may be discovered. In the following pages I have attempted such a classification of verified phenomena, accounts of which I find in the literature current on the subject; and I have tentatively formulated a working hypothesis for the systematic study of all classes of psychic phenomena. It will be observed that I have availed myself largely of the labors of others, instead of confining myself to experimental researches of my own. I have done this for two reasons: _first_, that I might avoid the accusation of having conducted a series of experiments for the purpose of sustaining a pet theory of my own; and _second_, because I hold that substantial progress cannot be made in science until one is ready to accord due credit to human integrity, and to give due weight to human testimony. In conclusion, I desire to say that I claim no credit for this work, save that which is due to an honest desire to promote the truth for its own sake. Sincerely believing in the correctness of my hypothesis, I have not hesitated to follow it to its legitimate conclusion in every field which I have entered. If at the close of the book I have seemed to trespass upon the forbidden field of theological discussion, it was not for the purpose of sustaining any preconceived opinions of my own; far from it. It was because I was irresistibly led to my conclusions by the terms of my hypothesis and the inflexible logic of its application. I cannot but be aware that my conclusions sometimes oppose the preconceived opinions of others. But no one who accepts my hypothesis as the true one will be compelled more frequently than I have been to renounce his former convictions. T.J.H. WASHINGTON, D.C. October 21, 1892. CONTENTS. CHAPTER I. INTRODUCTORY. PAGE Necessity of a Working Hypothesis.--The Newtonian Hypothesis.--The Atomic Theory.--A Psychological Hypothesis necessary.--Theories of Hypnotism and Mesmerism.--Spiritism.--Mental Therapeutics.--Liébault's Law of Suggestion.--Duality of Mind.--A Working Hypothesis for Psychology formulated.--Its Three Terms 19 CHAPTER II. DUALITY AND SUGGESTION.