We recognize and accept this cyclic return of time in such familiar manifestations of it as Nature affords in _periodicity_. We recognize it also in our mental and emotional life, when the periods can be co-ordinated with known physical phenomena, as in the case of the wanderlust which comes in the mild melancholy of autumn, the moods that go with waning day, and winter night. It is only when these recurrences do not submit themselves to our puny powers of analysis and measurement that we are incredulous of a larger aspect of the law of time-return. Sleep for example, is not less mysterious than death which, too, may be but "a sleep and a forgetting." The reason that sleep fails to terrify us as death does is because experience has taught that _memory leafs the chasm_. Why should death bedreaded any more than bedtime? Because we fear that we shall forget. But do we really forget? As Pierre Janet so tersely puts it, "Whatever has gone into the mind may come out of the mind," and in a subsequent chapter this aphorism will be shown to have extension in a direction of which the author of it appears not to have been aware. Memory links night to night and winter to winter, but such things as "the night-time of the spirit" and "the winter of our discontent" are not recognized as having either cause or consequence. Now though the well-springs of these states of consciousness remain obscure, there is nothing unreasonable in believing that they are recrudescences of far-off, forgotten moods and moments; neither is it absurd to suppose that they may be related to the movements and positions of the planets, as night and winter are related to the axial and orbital movements of the earth. But there are other, and even more interesting, evidences of time curvature in consciousness. These lead away into new regions which it is our pleasure now to explore. VI SLEEP AND DREAMS SLEEP