Larger context for LACK in Corpus USbrown_UKbncw/US_brown.txt
Now what is perfect motion?
It must, apparently, be motion without termini.
Because motion which begins and ends at discrete places would (e.g. for Aristotle) be incomplete.
Circular motion, however, since it is eternal and perfectly continuous, lacks termini.
It is never motion towards something.
Only imcomplete, imperfect things move towards what they lack. Perfect, complete entities, if they move at all, do not move towards what they lack. They move only in accordance with what is in their natures.
Thus, circular motion is itself one of the essential characteristics of completely perfect celestial existence.
To return now to the four-element physics, a mixture of muddy, frothy water will, when standing in a jar, separate out with earth at the bottom, water on top, and the air on top of that.
A candle alight in the air directs its flame and smoke upwards.
This gives a clue to the cosmical order of elements.
Thus earth has fallen to the center of the universe.
It is covered (partly) with water, air is atop of that.
Pure fire (the stars) is in the heavens.