But by the side of the physiological theory legitimately exist as possibilities a psychological one and a psycho-physical one. It is the doctrine of the latter theories that not only are physical vestiges left behind in the cortex of the brain after every perception, but also psychical dispositions to the formation of ideas and images; and that it is possible for images of all kinds to continue to exist without distinctly attaining to consciousness. These theories distinguish between degrees of luminosity in our percepts and images, the three most important degrees of which I have designated as consciousness, subconsciousness, and unconsciousness. There exists a gradation of degrees of consciousness, and the fully-conscious course of mental representation is everywhere conditioned by its connection with the obscured spheres beyond. Our attention surveys but a small area, on the boundary lines of which the altitudes of consciousness decrease, and finally approach the zero point. I say _approach_, for they never reach it. Our experiments with the magic mirror in fact show us how the oldest impressions, and impressions of ridiculous insignificance, after long long years awake as it were from the slumber of the fabled Sleeping Beauty. If our millions of perceptions were to live on in _consciousness_ we should no longer have a past, but live in a continuous celestial present; but were the operation of consciousness so limited that it destroyed great numbers of images, the very facts upon which the belief in supernatural powers rests, would lose their only rational explanation. One result of our study of crystal-visions is assuredly this, that we shall have to erase the word "forgotten" with all its derivatives from the dictionary, and at the most employ the phrase "not remembered." With more ardent yearning than ever before will we long for a river of Lethe, and join with our whole hearts in the cry of Themistocles, "O that some one might teach me the art of forgetting!"