This goes on through the whole of the five stages, so that when we get down to the physical plane, we find an atom showing a wall of denser matter, within it the involved life and without it the magnetic field, made up of the higher tanmâtras and their atomic sheaths. The Prithivî atom hence consists of its own tanmâtra plus the matter and the life of Apas; the matter and life of Agni; the matter and life of Vâyu; the matter and life of A'kâsha: so that on the physical plane, the physical atom is a mass of five interpenetrating spheres in which is present as life the whole of the matter and the life of the worlds above it, the envelope, or wall, of the physical atom alone showing forth any characteristics of the physical world--a fact inexpressibly important for evolution. For, each of those sheaths or koshas--as the student of Vedânta calls them, and there is no better word--every one of them is latent in and around the physical atom; and in the upward evolution, every one of them becomes active and strong as evolution proceeds, sheath after sheath being vitalised. How could these koshas, or sheaths, of ours learn to respond to the vibrations of the evolving life, unless every one of them was latently present in us, waiting to be brought into activity? The root of that possibility lies in the atom itself, with all its interpenetrating spheres of life and matter, the sheaths that are within it and around it. That is not the only thing which we understand; as this conception grows clear, we understand a phrase that had often puzzled us in the old days, that "the spirit is senseless on the plane of matter." What does that mean? The spirit, the very essence of consciousness, senseless and helpless on the plane of matter! Why? Because if you take spirit as pure spirit, the intermediate sheaths are not there by which the matter-vibrations are able to reach it, and without these sheaths it is unable to receive and respond to the vibrations of physical matter. It remains unconscious of their very existence, there being no bridge by which they can pass over and affect that life. This is really a perfectly simple statement of Madame Blavatsky's, but it is one that I have heard challenged over and over again as entirely meaningless, as conveying no idea, for how could consciousness be unconscious in any region? A little more knowledge would make us less rapid in our condemnation of our betters. That idea, then, we will take to help us in the first conception of how evolution can take place.