  The real cohomology of the space of imbeddings of S^1 into R^n, n>3, is
studied by using configuration space integrals. Nontrivial classes are
explicitly constructed. As a by-product, we prove the nontriviality of certain
cycles of imbeddings obtained by blowing up transversal double points in
immersions. These cohomology classes generalize in a nontrivial way the
Vassiliev knot invariants. Other nontrivial classes are constructed by
considering the restriction of classes defined on the corresponding spaces of
immersions.
