A little further on he learns that matter as he knows it is only
a minute portion of the great universe of matter--the few chords
that can be struck on the five strings of his senses, and limited
to one octave or key.

Whether the particular matter he investigates has a solid, a
liquid, or a gaseous form depends upon its rate of vibration. If
it is a liquid, by raising its rate of vibration one third it
becomes a gas; by reducing it one third it becomes a solid.

Each kind of matter has vibration only through one octave. It is
known to us only by its vibration in that octave. Each kind of
matter has a different octave--is set on a higher or lower key,
so to speak, but all octaves of vibration are between the highest
of hydrogen gas and the lowest of carbon.

In mechanical compounds, such as air or brass, the rate of
vibration of the compound is the least common multiple of the two
or more rates. In chemical compounds, such as water or alcohol,
the rate is that of the highest, the others uniting in harmonic
fractions.

All matter as we know it through our senses--prakriti, as it is
called in the Secret Doctrine to distinguish it from non-sensual
matter--is the vibration of an universal Something, we do not
know what, through these different octaves. The elementary
substances (so-called) are one and the same thing--this
Something--in different keys and chords of vibration; keys that
run into one another, producing all sorts of beautiful harmonies.