  We study the rational approximation properties of special manifolds defined
by a set of polynomials with rational coefficients. Mostly we will assume the
case of all polynomials to depend on only one variable. In this case the
manifold can be viewed as a Cartesian product of polynomial curves and it is
possible to generalize recent results concerning such curves with similar
concepts. There is hope that the method leads to insights on how to treat more
general manifolds defined by arbitrary polynomials with rational coefficients.
