The Collaborative International Dictionary of English v.0.48:

Equability \E`qua*bil"i*ty\, n. [L. aequabilitas, fr.
   aequabilis. See Equable.]
   The quality or condition of being equable; evenness or
   uniformity; as, equability of temperature; the equability of
   the mind.
   [1913 Webster]

         For the celestial bodies, the equability and constancy
         of their motions argue them ordained by wisdom. --Ray.
   [1913 Webster]