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Two new formulae for the $(-2)$ moment of the photo-absorption cross section,$\sigma_{_{-2}}$, have been determined, respectively, from the 1988 compilationof Dietrich and Berman and a mass-dependent symmetry energy coefficient,$a_{sym}(A)$. The data for $A\gtrsim50$ follow, with a {\small $RMS$} deviationof 6\%, the power-law $\sigma_{_{-2}}=2.4 A^{5/3}$$\mu$b/MeV, which is inagreement with Migdal's calculation of $\sigma_{_{-2}}=2.25A^{5/3}$$\mu$b/MeVbased on the hydrodynamic model and the $\sigma_{_{-2}}$ sum rule. Theadditional inclusion of $a_{sym}(A)$ provides a deeper insight to the nuclearpolarization of $A\geqq10$ nuclei.

New formulae for the $(-2)$ moment of the photo-absorption cross section, $\sigma_{_{-2}}$