The Sphere governing magical energy and, by extension, the fundamental makeup of many things. Adepts and Masters of this Sphere are in high demand according to 1st ed core. It enables mages to sense magickal energy, move Quintessence, empower objects, make temporary phantom objects, influence Nodes, empower and drain objects and living things, etc.
The Celestial Chorus and the Syndicate (in later editions) take an interest in this Sphere.