but neither of these can be touched by the highest clairvoyant
investigations at present possible for us. The third sphere, whose atoms
contain 2,401 bubbles, is called the spiritual world, because in it
functions the highest Spirit in man as now constituted. The fourth is the
intuitional world, [Previously called in Theosophical literature the
buddhic plane.] because from it come the highest intuitions. The fifth is
the mental world, because from its matter is built the mind of man. The
sixth is called the emotional or astral world, because the emotions of man
cause undulations in its matter. (The name astral was given to it by
mediæval alchemists, because its matter is starry or shining as compared to
that of the denser world.) The seventh world, composed of the type of
matter which we see all around us, is called the physical.

The matter of which all these interpenetrating worlds are built is
essentially the same matter, but differently arranged and of different
degrees of density. Therefore the rates at which these various types of
matter normally vibrate differ also. They may be considered as a vast gamut
of undulations consisting of many octaves. The physical matter uses a
certain number of the lowest of these octaves, the astral matter another
group of octaves just above that, the mental matter a still further group,
and so on.

Not only has each of these worlds its own type of matter; it has also its
own set of aggregations of that matter--its own substances. In each world
we arrange these substances in seven classes according to the rate at which
their molecules vibrate. Usually, but not invariably, the slower
oscillation involves also a larger molecule--a molecule, that is, built up
by a special arrangement of the smaller molecules of the next higher
subdivision. The application of heat increases the size of the molecules
and also quickens and amplifies their undulation, so that they cover more