The relationship between Gurdjieff's enneagram as related in my article, Tone-constellations of the enneagram, and Rudolf Steiner's understanding both of the nature of the interval, and of the processeses of 'cosmic nutrition,' have been an area of deep interest for me. The relationship between insights developed out of Steiner's work and the symbolism of the enneagram, is particularly pregnant in that Gurdjieff's primary use of the enneagram symbolism was to describe his 'food-factory' or 'octaves of nutrition' in which sense impressions provided the impulse to advance the 'evolution' of the energy of food and air into higher 'elements'.

Steiner's own teachings - scattered here and there - concerning the 'cosmic nutrition stream' that enters via the senses, as well as the transformation from a 'yoga of breath' (pranayama) of ancient times to a 'yoga of cognition', and of an inbreathing of 'vivifying' 'soul-light substance' into the senses since the time of the Mystery of Golgatha - can greatly illuminate the questions stimulated by Gurdjieff's exposition of the enneagram.

The application of musical symbolism to the enneagram is intended as an exploration and contemplation of the of the world-creative power of tone.

• Useful works in approaching this sphere include Hans Lauer's article regarding the changing experience of the various musical interval's during mankind's development. In his Evolution of Music Through Changes in Tone-Systems, (translated by Joscelyn Godwin in his Cosmic Music, Inner Traditions) (Godwin has edited a number of interesting works in speculative music, including translation's of Fabre D'Olivet).
  
  
• Armin Husemann's The Harmony of the Human Body (Floris Books) provides an excellent series of insights into the nature of the different intervals as creative, formative forces, and how they express various creative relationships between the etheric and astral. It provides and application of the intervals to the development of living forms.
  
  
• Steiner's own The Inner Nature of Music and The Experience of Tone. (Rudolf Steiner Press) contains some of Steiner's seminal insights in this area.
  
  
• Heiner Ruland's Expanding Tonal Awareness (Rudolf Steiner Press) takes up where Lauer's article leaves off, and provides an in-depth historical perspective on the development of various musical systems.
  
  
• Sound and Symbol, by Victor Zuckerkandl, (Princeton/Bollingen) provides an insightful journey into the qualities of musical sound, with insights fruitful for their application in speculative music.
  
  
• The Doctrine of Vibration, Mark Dyczkowski, (SUNY Press), is a survey of the Kashmir Shaivism and the Spanda Doctrine that understands the self as the pulsing, active force in all reality.