The tendency in fluids to mix, or become equably diffused,
   when in contact. It was first observed between fluids of differing
   densities, and as taking place through a membrane or an intervening
   porous structure. The more rapid flow from the thinner to the thicker
   fluid was then called endosmose, and the opposite, slower current,
   exosmose. Both are, however, results of the same force. Osmose may be
   regarded as a form of molecular attraction, allied to that of adhesion.