Before revision:  The strength of DNA-DNA short range attraction  , mediated by Mg^{+2}, is found to be -0.004 k_BT per nucleotide base  .
After revision:  The strength of DNA-DNA short range attraction , mediated by Mg^{+2}, is found to be -0.004 k_BT per nucleotide base . This and other fitted parameters agree well with known values from other experiments and computer simulations. The parameters are also in aggreement qualitatively with values for tri- and tetra-valent counterions .