Similarly, replacing the real charge Q with a medium of density ρ ρ 1 and polarizability α α 1 gives an expression for α α 1 ρ ρ 1 . Using these two relations, we may restate our theory in terms of an effective Hamaker constant. Specifically, using McLachlan's generalized theory of VDW forces the Hamaker constant for an interaction potential of the form U ( r ) = − − C / r n between two bodies at temperature T is