A very large and very interesting class of occult or psychic phenomena is that known under the very general classification of "Clairvoyance," which term we have thought it advisable to employ in this sense in this book, notwithstanding the technical objections urged by some against such a general usage. The term "Clairvoyance" really means "clear seeing," or "clear sight," but its special meaning, established by long usage, is "A power of discerning objects not perceptible to the normal senses." When it comes to the technical use of the term by students and teachers of psychic research and occultism, however, there is found a confused meaning of the term, some employing it in one sense, and others in another one. Accordingly, it is perhaps as well to explain the particular usage adopted and followed in this book. Clairvoyance Defined. The English Society for Psychical Research, in its glossary, defines the term as follows: "The faculty or act of perceiving, as though visually, with some coincidental truth, some distant scene; it is used sometimes, but hardly properly, for transcendental vision, or the perception of beings regarded as on another plane of existence." A distinguished investigator along psychic lines, in one of her reports to the English Society for Psychical Research, has given the following definition of this term as employed by her in her reports, viz., "The word 'clairvoyant' is often used very loosely, and with widely different meanings. I denote by it a faculty of acquiring supernormally, BUT NOT BY READING THE MINDS OF PERSONS PRESENT, a knowledge of facts such as we normally acquire by the use of our senses. I do not limit it to knowledge that would normally be acquired by the sense of sight, nor do I limit it to a knowledge of present facts. A similar knowledge of the past, and if necessary, of future events, may be included. On the other hand, I exclude the mere faculty of seeing apparitions, which is sometimes called clairvoyance." The last stated definition agrees almost perfectly with the views of the writer of the present book, and the term "Clairvoyance" is used here in the particular sense indicated by such definition. The student of this book, therefore, is asked to distinguish Clairvoyance, on the one hand, from the phenomena of Telepathy or Thought Transference, and, on the other hand, from the phenomena of communication with entities on other planes of existence, including the perception of apparitions. The Phenomena of Clairvoyance. The phenomena of Clairvoyance may be subdivided (a) according to methods employed, and also (b) according to general distinctions. The said classifications follow: