timate atoms of matter are thought to float, like
motes in a sunbeam, and light, heat and electricity are supposed to be its
vibrations.

Theosophical investigators, using methods not at the disposal of physical
science, have found that this hypothesis includes under one head two
entirely different and widely separated sets of phenomena. They have been
able to deal with states of matter higher than the gaseous and have
observed that it is by means of vibrations of this finer matter that light,
heat and electricity manifest themselves to us. Seeing that matter in these
higher states thus performs the functions attributed to the ether of
science, they have (perhaps unadvisedly) called these states etheric, and
have thus left themselves without a convenient name for that substance
which fulfils the other part of the scientific requirements.

Let us for the moment name this substance _koilon_, since it fills what we
are in the habit of calling empty space. What mulaprakrti, or
"mother-matter," is to the inconceivable totality of universes, koilon is
to our particular universe--not to our solar system merely but to the vast
unit which includes all visible suns. Between koilon and mulaprakrti there
must be various stages, but we have at present no direct means of
estimating their number or of knowing anything whatever about them.

In an ancient occult treatise, however, we read of a "colorless spiritual
fluid" "which exists everywhere and forms the first foundation on which our
solar system is built. Outside the latter, it is found in its pristine
purity only between the stars [suns] of the universe.... As its substance
is of a different kind from that known on earth, the inhabitants of the
latter, seeing _through it_, believe, in their illusion and ignorance, that
it is empty space. There is not one finger's breadth of void space in the
whole boundless universe."[21] "The mother-substance" is said, in this
treatise, to produce this aether of space as its seventh grade of density,
and all objective suns are said to have this for their "substance."

To any power of sight which we can bring to bear upon it, this koilon
appears to be homogeneous, though it is probably nothing of the kind, since
homogeneity can belong to the mother-substance alone. It is out of all
proportion denser than any other substance known to us, infinitely
denser--if we may be pardoned the expression; so much denser that it seems
to belong to another ty