muscles adjust themselves so as to see clearly. But here again all sorts of factors enter in. Innumerable objects are in our field of vision, but only some (at most) are interesting to us. If some one says “look, there’s a snake”, we adjust our eyes afresh and obtain a new “sensation”. Then, when the purely visual part is finished, there are stimulations, by association, of other centres in the brain. There are pictures, in Köhler’s book, of apes watching other apes on the top of insecure piles of boxes, and the spectators have their arms raised in sympathetic balancing movements. Any one who watches gymnastics or skilful dancing is liable to experience sympathetic muscular contractions. Any visual object that we might be touching will stimulate incipient touch reactions, but the sun, moon, and stars do not. Conversely, visual reactions may be stimulated through association with other stimuli. When motor-cars were still uncommon, I was walking one day with a friend when a tire punctured in our neighbourhood with a loud report. He thought it was a revolver, and averred that he had seen the flash. In dreams, this sort of mechanism operates uncontrolled. Some stimulus--say the noise of the maid knocking at the door--becomes interpreted in fantastic ways which are governed by association. I remember once dreaming that I was in an inn in the country in Germany and was wakened by a choir singing outside my window. Finally I really woke, and found that a spring shower was making a very musical noise on the roof. At least, I heard a very musical noise, and now re-interpreted it as a shower on the roof. This hypothesis I confirmed by looking out of the window. In waking life we are critical of the interpretative hypotheses that occur to us, and therefore do not make such wild mistakes as in dreams. But the creative, as opposed to the critical, mechanism is the same in waking life as it is in dreams: there is always far more richness in the experience than the sensory stimulus alone would warrant. All adaptation to environment acquired during the life of the individual might be regarded as learning to dream dreams that succeed rather than dreams that fail. The dreams we have when we are asleep usually end in a surprise: the dreams we have in waking life are less apt to do so. Sometimes they do, as when pride goes before a fall; but in that case they are regarded as showing maladjustment, unless there is some large external cause, such as an earthquake. One might say that a person properly adapted to his environment is one whose dreams never end in the sort of surprise that would wake him up. In that case, he will think that his dreams are objective reality. But if modern physics is to be believed, the dreams we call waking perceptions have only a very little more resemblance to objective reality than the fantastic dreams of sleep. They have some truth, but only just so much as is required to make them useful.