  Series for the Wilson functions of an ``environmentally friendly''
renormalization group are computed to two loops, for an $O(N)$ vector model, in
terms of the ``floating coupling'', and resummed by the Pad\'e method to yield
crossover exponents for finite size and quantum systems. The resulting
effective exponents obey all scaling laws, including hyperscaling in terms of
an effective dimensionality, ${d\ef}=4-\gl$, which represents the crossover in
the leading irrelevant operator, and are in excellent agreement with known
results.
