The definitions which one applies to hypnotism depend on those theoretical views held on this subject. If we throw overboard as far as possible the ballast of undigested or superstitious nonsense which is claimed for the phenomena belonging to this question, and which is scattered broadcast in the widespread trashy literature on the so-called occultism, only three theories or explanations, differing in principle, of the facts briefly recited above remain.

1. An external invisible agent penetrates into the body, and especially into the nervous system, influences the organism, and introduces into the latter something which is foreign to it; it may even be the knowledge of lifeless nature or of other living beings.1 One formerly regarded this agent as a fluid, and the laity still speak of it as such; spiritualists call it an immaterial spirit, and in the language of modern times it would be termed a still unknown physical force. Or the thoughts and mental processes of one person reach by means of such an agent the knowledge of the mind of another person, without the intermediation of the speech of sound, of writing, or of signs of the first person, or by means of the organs of sense of the second. This is Mesmer's theory. Mesmer called the supposed agent magnetism, and especially "animal magnetism," when it appeared to be derived from the human or animal organism (the more so when it seemed to be derived from the magnetizer). This theory is supported still in certain circles by enthusiastic and even fanatic adherents, and is based on those phenomena referred to under (2), and those quoted as doubtful, alleged immaterial facts. If it were true, it would without doubt seriously influence our scientific knowledge, for the consistent ignoring on the part of science up to the present time of this unknown something, of this unknown force, would necessarily have caused an error in our results hitherto, in the same way as an important factor, if forgotten, would have done. The law of energy could not hold good, for such influences would of necessity always lead to error. But as Science, as a result of her extensive practical results, offers daily increasing proof of her intrinsic truth, one has reason to distrust Mesmer's theory, and to require of it unambiguous, unimpeachable proofs. Let us consider briefly how matters lie.

1 It is not absolutely uninteresting to compare these views with those of the physiologist Albrecht Bethe, who assumes the intervention of "unknown powers" in the method in which insects find their way about, instead of employing the conclusion of analogy, which requires less seeking, and accepting that insects use their organs of sense, as well as their memory and the association of their engrains, simply as we do. (Forel, "The Psychical Capabilities of Ants," loc. at.)

Mesmer and his school have been so completely contradicted by Braid and Liebeault as far as the facts referred to above as indisputable are concerned (see later) that it were vain to waste more time on this subject. The fluid theory takes umbrage behind the supposed facts even at the present time, which are guarded by the spiritualists, and which, according to the circles in which they are produced, are so intimately intermingled with blind fanaticism, with mental disturbances (hallucinations), with misconceived suggestions, with trickery and with superstition, that it is extremely difficult to subject them to a scientific investigation at present. The spirits and the fourth dimension of the spiritualists are the conceptions which would correspond to the unknown agent. The so-called "materialization of spirits," which probably depends partly on hallucinations of feeling and partly on deceit, indicates the consummation of the nonsense of dualistic conceptions. In order to demonstrate the reality of an immaterial, energyless spirit, one wishes to render it material, and containing energy.

As far as the "photographs"of "spirits" are concerned, there is a very simple photographic method of producing such pictures. I have Been an excellent spirit photograph which was taken by an honest photographer without a "spirit"! The sort of trick which is similar to those employed by conjurers plays a part here which must not be undervalued.

A series of apparently supernatural phenomena which are supposed to speak in favor of Mesmer's or allied theories are, as has already been stated, constantly being brought forward by upright, trustworthy people. I can mention the so-called thought-reading, improperly called "mental suggestion "; clairvoyance; seeing or guessing of what is taking place at a distance; the so-called presentiments and "fortune-telling," inter alia. These supposed phenomena are collectively styled "telepathy".

"Phantasms of the Living"1 is an extraordinary book from the above-mentioned point of view. In it no less than six hundred observations on visions, dreams, presentiments, and the like, which were fulfilled, are recorded. Exact inquiries are said to have been made into the reliability of the sources of the accounts, and only clear accounts of trustworthy persons were supposed to have been accepted. A review of this book was published in the Revue des Deux Mondes of May 1, 1888. Everyone can meet with several similar observations among his own friends, and, without doubt, among trustworthy persons.1 One must further not fail to mention in this place that in the history of the world a considerable amount of telepathy is recorded. One meets with the belief in the so-called sympathetic influences and in the fulfillment of presentiments up to the present time and in spite of all enlightenment, even in professed atheists.

1 "Phantasms of the Living," by Gurney (Myers and Podmore, two vols. in 8vo.; Trubner, London, 1877).

The experiments of Ch. Richet are also interesting. He attempts to prove the influence of the thinking of one individual on the thinking of another in a certain direction without external appearances which could he sensorily perceived. It appears to me, however, that the proofs are extremely imperfect, and the probability calculation employed very unconvincing. The later investigations of von Schrenk-Notzing, Flournoy, and others, have also failed to arrive at definite conclusions.