It is admitted that some of these pass through solid matter with perfect ease, so that this enables us to account scientifically for some of the peculiarities of astral vision, though those minds to which the theory of the fourth dimension commends itself find in it a neater and more complete explanation. It is clear that the mere possession of this astral vision by a being would at once account for his capability to produce many results that seem very wonderful to us--such, for example, as the reading of a passage from a closed book; and when we remember, furthermore, that this faculty includes the power of thought-reading to the fullest extent, and also, when combined with the knowledge of the projection of currents in the astral light, that of observing a desired object in almost any part of the world, we see that a good many of the phenomena of clairvoyance are explicable even without rising above this level. Of course true, trained, and absolutely reliable clairvoyance calls into operation an entirely different set of faculties, but as these belong to a higher plane than the astral, they form no part of our present subject. The faculty of accurate prevision, again, appertains altogether to that higher plane, yet flashes or reflections of it frequently show themselves to purely astral sight, more especially among simple-minded people who live under suitable conditions--what is called "second-sight" among the Highlanders of Scotland being a well-known example. Another fact which must not be forgotten is that any intelligent inhabitant of the astral plane is not only able to perceive these etheric vibrations, but can also--if he has learnt how it is done--adapt them to his own ends or himself set them in motion. [Sidenote: Astral Forces.] [Sidenote: Etheric Currents.] [Sidenote: Etheric Pressure.] [Sidenote: Latent Energy.] [Sidenote: Sympathetic Vibration.]