The mental world constitutes a region of our earth still more vast than the astral portion of it. As the astral sphere encloses the physical globe, the mental encompasses both, enclosing them and also interpenetrating them to the earth's center. The term "mental world" may seem confusing to some because we are accustomed to think of the mental and the material as being opposites. The mental world, or sphere, or plane, of theosophy, is a world of _matter_, not merely thought. It is matter, however, of such remarkable tenuosity that it may properly be called mind-stuff, and in its rarest levels it is said to be "formless" so far as the existence of what the physical senses know as form is concerned. All three of these worlds, or planes--the physical, astral and mental--are, then, worlds of matter, of form, of activity, of thought and of enterprise. They are concentric globes, the physical enclosed by the astral, and both physical and astral enclosed by the mental. Within and without all physical matter are both astral and mental matter. Every physical atom is surrounded and permeated by astral and mental matter. The relationship is precisely that which exists between the ether and the lower grades of physical matter. If the relationship of the three worlds--physical, astral and mental--is fully understood later confusion of thought will be avoided. Physical language is not capable of fully expressing much with which students of the occult must deal. Because there is nothing better for the purpose, words must be used that express but a part of the truth and may sometimes prove misleading unless the constitution and relationship of the three spheres is kept in mind. Thus, it is necessary to speak of higher and lower worlds, or planes, inner or outer, and of the soul coming "down" into the material world when, as a matter of fact, _no movement in space_ is under consideration. The astral is commonly spoken of as an inner plane and while it truly is so because it can be known only to astral senses by a withdrawal of the consciousness from its exterior, material body, it is also true that the astral world is outside the physical because it envelops it as the sea does a sponge. We usually speak of coming down from higher planes to lower and that may be true not only in the sense of changing the state of consciousness from higher vibrations to lower ones but it _could_ mean a journey in space from a point in the astral plane above the physical globe to a point at its surface. "Up" and "down" are relative, not absolute. "Down" for us is toward the earth's center and "up" is the opposite direction. A spire in the Occident and a spire in the Orient are both said to be pointing upward but they are pointing in opposite directions. On most parts of the earth's surface we have four directions, while at the poles there is, of course, but one direction--south or north, as the case may be. East, west and north disappear at the north pole. Reflection upon