The experiments with the Roentgen rays give us an example of the startling results which are produced when even a very few of these additional vibrations are brought within human ken, and the transparency to these rays of many substances hitherto considered opaque at once shows us one way at least in which we may explain such elementary clairvoyance as is involved in reading a letter inside a closed box, or describing those present in an adjoining apartment. To learn to see by means of the Roentgen rays in addition to those ordinarily employed would be quite sufficient to enable anyone to perform a feat of magic of this order. So far we have thought only of an extension of the purely physical senses of man; and when we remember that a man's etheric body is in reality merely the finer part of his physical frame, and that therefore all his sense organs contain a large amount of etheric matter of various degrees of density, the capacities of which are still practically latent in most of us, we shall see that even if we confine ourselves to this line of development alone there are enormous possibilities of all kinds already opening out before us. But besides and beyond all this we know that man possesses an astral and a mental body, each of which can in process of time be aroused into activity, and will respond in turn to the vibrations of the matter of its own plane, thus opening up before the Ego, as he learns to function through these vehicles, two entirely new and far wider worlds of knowledge and power. Now these new worlds, though they are all around us and freely inter-penetrate one another, are not to be thought of as distinct and entirely unconnected in substance, but rather as melting the one into the other, the lowest astral forming a direct series with the highest physical, just as the lowest mental in its turn forms a direct series with the highest astral. We are not called upon in thinking of them to imagine some new and strange kind of matter, but simply to think of the ordinary physical kind as subdivided so very much more finely and vibrating so very much more rapidly as to introduce us to what are practically entirely new conditions and qualities. It is not then difficult for us to grasp the possibility of a steady and progressive extension of our senses, so that both by sight and by hearing we may be able to appreciate vibrations far higher and far lower than those which are ordinarily recognised. A large section of these additional vibrations will still belong to the physical plane, and will merely enable us to obtain impressions from the etheric part of that plane, which is at present as a closed book to us. Such impressions will still be received through the retina of the eye; of course they will affect its etheric rather than its solid matter, but we may nevertheless regard them as still appealing only to an organ specialized to receive them, and not to the whole surface of the etheric body.