This well-known fact, that we cannot measure dreams by our time scale, proves that subjective time does not correspond with objective, and that the "dream organ" of consciousness has a time scale of its own. If in our waking state we experience one kind of time, and in dreams quite another, the solution of the mystery should be sought in the _vehicle_ of consciousness, for clearly the limit of impressionability or power of response of the vehicle establishes the time scale, just as the size of the body with relation to objects establishes the space scale. Time must be different for the ant and the elephant, for example, as space is different. Our sense of time is wholly dependent upon the rapidity with which impressions succeed one another. Were we capable of receiving only one impression an hour, like a bell struck every hour with a hammer, the ordinary term of life would seem very short. On the other hand, if our time sense were always as acute as it is in dreams, uncounted aeons would seem to be lived through in the interval between childhood and old age. Imagine a music machine so cunningly constructed and adjusted as not only to sound each note and chord in its proper sequence and relation, but to regulate also the duration of the sound vibration. If this machine were operated in such a manner as to play, in a single second of time, the entire overture of an opera which would normally occupy half an hour, we should hear only an unintelligible noise a second long. This would be due to no defect in the _sound-producing_ mechanism, but to the limitations of the _sound-receiving_ mechanism, our auditory apparatus. Could this be altered to conform to the unusual conditions--could it capture and convey to consciousness every note of the overture in a second of time--that second would seem to last half an hour, provided that every other criterion for the measurement of duration were denied for the time being. Now dreams _seem_ long: we only discover afterwards and by accident their almost incredible brevity. May we not--must we not--infer from this that the body is an organ of many stops and more than one keyboard, and that in sleep it gives forth this richer music. The theory of a higher-dimensional existence during sleep accounts in part for the great longing for sleep. "What is it that is much desired by man, but which they know not while possessing?" again asks Leonardo. "It is sleep," is his answer. This longing for sleep is more than a physical longing, and the refreshment it brings is less of the flesh than of the spirit. It is possible to withstand the deprivation of food and water longer and better than the deprivation of sleep. Its recuperative power is correspondingly greater.