In connection with sounds, you will not only "in your mind's eye" _see_ the places where they originate, and _feel_ the course they are taking, but you will actually, functionally (in the mode of spiritually seeing and feeling), "see" and "feel" them. This vision and this feeling is far from being perfect, however,--not being accustomed to thus seeing and feeling,--but it may, when continuously exercised, become so in the course of time. While in this state, besides seeing the places interiorly, you may also see them exteriorly, by reflection as it were, and in a reverse order, "as in a looking-glass," in which case it is still an interior vision reflected exteriorly. As a matter of fact, I not only believe, but positively _know_, that _every exterior functional surface has a corresponding posterior one_. Whenever a thing is brought _home_ to us, either through our organs of seeing, hearing, feeling, smelling, or tasting, the outer surface of such respective organ constitutes the positive factor for such action, while its inner surface constitutes the negative factor thereof. Whenever the outer world is excluded, however, as during thought, introspection, and in our sleep, the inner surface of any of these organs becomes the positive, and the outer surface the negative, factor. In thus saying, "I see with the inner surface of my eyes," I do not mean this figuratively only, but literally, functionally, as well; as I could not see these places and locate them internally nor could I see any subject or object with "my mind's eye," if the faculty of seeing were not actually given to the posterior surface of the eye. This will become clear when you consider that you will altogether fail to see internally when you attempt to use the _anterior_ surface of your eye for the purpose of _internal_ vision. Thus, the phenomena of vision which accompany thought or dreams, during sleep as well as in our waking moments, are not merely spiritual, but, in the sense of internal functional vision, are also material, so to say. _All_ thought, in fact, is more or less of this same nature. We use the posterior surfaces of our organs of sense more frequently, in consequence, than we do their corresponding anterior surfaces. Physiologists will say there is no such a thing as an inner surface of the eye capable of seeing. This does not alter the fact that I actually, functionally, see with the posterior surface of my eyes, and that everybody else does the same thing.