  We investigate the structure of Polchinski's formulation of the flow
equations for the continuum Wilson effective action.
  Reinterpretations in terms of I.R. cutoff greens functions are given. A
promising non-perturbative approximation scheme is derived by carefully taking
the sharp cutoff limit and expanding in `irrelevancy' of operators.
  We illustrate with two simple models of four dimensional $\lambda \varphi^4$
theory: the cactus approximation, and a model incorporating the first
irrelevant correction to the renormalized coupling. The qualitative and
quantitative behaviour give confidence in a fuller use of this method for
obtaining accurate results.
