  The dynamic electric dipole polarizability function for the magnesium atom is
formed by assembling the atomic electric dipole oscillator strength
distribution from combinations of theoretical and experimental data for
resonance oscillator strengths and for photoionization cross sections of
valence and inner shell electrons. Consistency with the oscillator strength
(Thomas-Reiche-Kuhn) sum rule requires the adopted principal resonance line
oscillator strength to be several percent lower than the values given in two
critical tabulations, though the value adopted is consistent with a number of
theoretical determinations. The static polarizability is evaluated. Comparing
the resulting dynamic polarizability as a function of photon energy with more
elaborate calculations reveals the contributions of inner shell electron
excitations. The present results are applied to calculate the long-range
interactions between two and three magnesium atoms and the interaction between
a magnesium atom and a perfectly conducting metallic plate. Extensive
comparisons of prior results for the principal resonance line oscillator
strength, for the static polarizability, and for the van der Waals coefficient
are given in an Appendix.
