Arithmetic,  Geometry,  Music, and  Astronomy
 ARITHMETIC —
Number in itself, which is a pure abstraction; that is, outside of space and time.
The Quadrivium with Gene Odening, Gnostic Media Podcast episode #050 (start here)
Quadrivium – Number, Geometry, Music, & Cosmology with John Martineau, Gnostic Media Podcast episode #103 (intermediate)
The Golden Ratio with Dr. Scott Oslen, Gnostic Meida podcast episode #108 (advanced)