Originally published in 1892. PREFACE: My primary object in offering it to the public is to assist in bringing Psychology within the domain of the exact sciences. That this has never been accomplished is owing to the fact that no successful attempt has been made to formulate a working hypothesis sufficiently comprehensive to embrace all psychic phenomena. It has, however, long been felt by the ablest thinkers of our time that all psychic manifestations of the human intellect, normal or abnormal, whether designated by the name of mesmerism, hypnotism, somnabulism, trance, spiritism,...