Electronic Music No.21 by William Lennox is an orchestral sized composition and is Metaphysica Empirica II.

This can be seen as a direct development of Metaphysica Empirica I, but this composition has a more specific direction of consolidation particularly in the control of the Harmony and in the terms of the function of Empirical MetaPhysics has the role of providing the new home for the Symphonic form with a more direct application in providing an explicit pathway to the inspirational role and permanence of this music.

In its full form the composition has a duration of 3 hours and 4 minutes.

Though there are a wide variety of performance forms of this composition.

Ranging from the performance of individual or groups of areas of the composition with a minimum duration of 32 minutes, to 16 subcompositions of Electronic Music No.21 ranging in duration of 3 to 12 minutes.

7 Developed sub-compositions of Electronic Music No.21 have been produced these are in the duration of 10 to 25 minutes and are named in the KnoxOdeon Sphere connecting up their performance with Crestime and the New Economics.

These have been designed for particular application in a non-formal atmosphere for repeated use in political or dance environments.

Metaphysica Empirica II is the calm and chance for redemption, before the storm and implication of Metaphysica Empirica III.