Before the dawn of history mankind was engaged in the study of dreaming. The wise man among the ancients was preeminently the interpreter of dreams. The ability to interpret successfully or plausibly was the quickest road to royal favor, as Joseph and Daniel found it to be; failure to give satisfaction in this respect led to banishment from court or death. When a scholar laboriously translates a cuneiform tablet dug up from a Babylonian mound where it has lain buried for five thousand years or more, the chances are that it will turn out either an astrological treatise or a dream book. If the former, we look upon it with some indulgence; if the latter with pure contempt. For we know that the study of the stars, though undertaken for selfish reasons and pursued in the spirit of charlatanry, led at length to physical science, while the study of dreams has proved as unprofitable as the dreaming of them. Out of astrology grew astronomy. Out of oneiromancy has grown - nothing.That at least was substantially true up to the beginning of the present century. Dream books in all languages continued to sell in cheap editions and the interpreters of dreams made a decent or, at any rate, a comfortable living out of the poorer classes. But the psychologist rarely paid attention to dreams except incidentally in his study of imagery, association and the speed of thought. But now a change has come over the spirit of the times. The subject of the significance of dreams, so long ignored, has suddenly become a matter of energetic study and of fiery controversy the world over.The cause of this revival of interest is the new point of view brought forward by Professor Bergson in the paper which is here made accessible to the English-reading public. This is the idea that we can explore the unconscious substratum of our mentality, the storehouse of our memories, by means of dreams, for these memories are by no means inert, but have, as it were, a life and purpose of their own, and strive to rise into consciousness whenever they get a chance, even into the semi-consciousness of a dream. To use Professor Bergson's striking metaphor, our memories are packed away under pressure like steam in a boiler and the dream is their escape valve.That this is more than a mere metaphor has been proved by Professor Freud and others of the Vienna school, who cure cases of hysteria by inducing the patient to give expression to the secret anxieties and emotions which, unknown to him, have been preying upon his mind. The clue to these disturbing thoughts is generally obtained in dreams or similar states of relaxed consciousness. According to the Freudians a dream always means something, but never what it appears to mean. It is symbolic and expresses desires or fears which we refuse ordinarily to admit to consciousness, either because they are painful or because they are repugnant to our moral nature. A watchman is stationed at the gate of consciousness to keep them back, but sometimes these unwelcome intruders slip past him in disguise.