Degree of strata of singular cubic surfaces

We determine the degree of some strata of singular cubic surfaces in the pr ojective space P-3. These strata are subvarieties of the P-19 parametrizing all cubic surfaces in P-3. It is known what their dimension is and that th ey are irreducible. In 1986, D. F. Coray and I. Vainsencher computed the de gree of the 4 strata consisting on cubic surfaces with a double line. To wo rk out the case of isolated singularities we relate the problem with (stati onary) multiple-point theory.