ble matter is _within_ the earth as
well as beyond it, interpenetrating every atom of physical matter to the
earth's center. Its grossest grade of matter is so rare, and its
vibrations so intense, that they cannot affect the physical senses and
therefore we remain unconscious of it while that matter moves freely
through all physical objects. We are unconscious of its life and
activities for precisely the same reason that we know nothing of the
messages of intelligence carried on the vibrations of the wireless
telegraph, although they pass through the room where we sit. We have no
sense organs with which it is possible to register such vibrations.
Messages conveying intelligence of tremendous import, involving the
movements of vast armies, the fall of empires and the destinies of great
nations, flow through the very space we occupy but we are wholly
unconscious of them. Even so we remain blind and deaf to the stupendous
activities of life and consciousness in the astral world,
notwithstanding the fact that it surrounds and permeates us while its
forms, unseen and unfelt, move through the physical world as freely as
water flows through a sieve.

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