Every natural body is moved according to one of these motions.
Every natural body is either simple or compounded.
Every simple motion is the motion of a simple[59] body.
Every simple body is moved with one motion according to nature.
DEFINITIONS.
That is heavy which is moved towards the middle.
That is light which is moved from the middle.
That is said to be moved in a circle which is continually borne from the same to the same.
Contrary motions are from contraries to contraries.