The primary object of this book is to assist in bringing Psychology within the domain of the exact sciences. It has 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, somnambulism, trance, spiritism, demonology, miracle, mental therapeutics, genius, or insanity, are in some way related ; and consequently, that they are to be referred to some general principle or law, which, once understood, will simplify and correlate the whole subject-matter, and possibly remove it from the domain of the supernatural.