Perhaps the most elementary fact about dream vision is the perpetual and unceasing change which it is undergoing at every moment. Sight is for most of us the chief sensory activity of sleeping as it is of waking life; the commonest kind of dream is mainly a picture, but it is always a living and moving picture, however inanimate the objects which appear in vision before us would be in real life. No man ever gazed at a dream picture which was at rest to his sleeping eye as are the pictures we gaze at with our waking eyes. So far as my own experience is concerned, I have rarely in sleep seen a sentence, a word, a letter written on a sheet of dream-paper which was not changing beneath the eye of sleep. I dream, for instance, that I wish to stamp a letter, and look in my pocket-book for a penny stamp; I am able to find stamps of other values, I am able to find penny stamps that are torn or defaced or of an antiquated type disused thirty years ago; all sorts of stamps, as well as little pictures resembling stamps, develop and multiply beneath my gaze; the stamp I seek remains unfound, probably because it had appeared at the beginning of the series and suggested all the rest. That is indicated by another dream (experienced, it may be noted, during the early stage of a cold in the head): I have to catch a train; I see my hat hanging on a peg among other hats, and I move towards it; but as I do so it has vanished; and I wander among rows of hats, of all shapes and sizes, but not one of them mine. Sleeping consciousness is a stream in which we never bathe twice, for it is renewed every second. It is this as much as any characteristic of the visual dream--for the mainly auditory or motor dream often presents less difficulty in this respect--which makes it so difficult to recall and reproduce. We are, as it were, gazing at a constantly revolving kaleidoscope in which every slightest turn produces a new pattern, somewhat resembling that which immediately preceded it--so that, if the kaleidoscope were conscious we should say that each picture had been suggested by the preceding pattern--but yet definitely novel.[12]