An electron correlation has been examined in detail for the 1s 2 -state of He and comparisons are made with the ground state of Li + , Be 2+ and B 3+ . An expression has been obtained for the partial Coulomb hole associated with any pair of occupied HF spin orbital for many electro n systems. The required partitioning of the correlated second order density matr ix was achieved here, up to and including the pair- correlation effects. Partial coulom b holes were determined in momentum space. The concept of partial coulomb holes and their collective presentation as surfaces has been demonstrated to be particularly informative. These surfaces enabled us to interpret correlation effects in momentum space providing a rationalization of the correlatio n mechanisms in each state.