It is, however, of the real dream--which is at times so intelligent that it has been called lucid, and at all events is reasonable, logical, and co-ordinate--that we wish to speak. In most cases this dream consists of a series of thoughts due to the soul in action in the astral body; it is sometimes the result of seeing mental pictures of the future[6] or else it represents quite another form of animistic activity, as circumstances and the degree of the dreamer's development permit.
It is in the lucid dream--whether belonging to normal or to abnormal sleep--that occur those numerous and well-known cases of visions past or future to be found in so many of the books dealing with this special subject.
To these same states of higher consciousness are due such productions as Walter Scott's _Ivanhoe_. The author, suffering from fever, wrote this work whilst in a kind of delirious condition; _Ivanhoe_ was printed before the recovery of the author, who, on reading it at a later date, had not the slightest recollection that it was his own production. (Ribot's _Maladies de la Mémoire_, p. 41.)
Walter Scott remembered nothing, because _Ivanhoe_ was the fruit of the astral consciousness impressed upon a brain which fever had rendered temporarily receptive to the higher vibrations.
There are certain peculiarities of the real dream which prove almost mathematically the superior nature of the vehicle which gives expression to it. This dream, for instance, is never of a fatiguing nature, however long it may appear to last, because it is only an instantaneous impression made upon the brain by the astral body, when the latter returns to the physical body, on awaking. On the other hand, the cerebral ideation of the waking state is fatiguing if intense or prolonged, or if the nervous system of the thinker is deprived of its normal power of resistance (_in neurasthenia_); the commonplace (_brain_) dream is also fatiguing if prolonged or at all vivid.
Another peculiarity is that a dream--the real dream--which would require several years of life on earth for its realisation, can take place in a second. The dream of Maury (_Le Sommeil et le Rève_, p. 161), who in half a second lived through three years of the French Revolution, and many other dreams of the same nature, are instances of this. Now, Fechner has proved, in his _Elemente der Psychophysik_, first, that a fraction of a second is needed for the sensorial contact to cause the brain to vibrate--this prevents our perceiving the growth of a plant and enables us to see a circle of fire when a piece of glowing coal is rapidly whirled round; secondly, that another fraction of a second is needed for the cerebral vibration to be transformed into sensation. We might add that a third fraction of a second is needed for sensation to be transformed into ideation, proving that in these special dreams there can have been no more than an instantaneous, mass impression of all the elements of the dream upon the brain,[7] and that the dream itself has been produced by the imaginative action of the soul in the astral body, an extremely subtle one, whose vibratory power is such as to transform altogether our ordinary notions of time and space.