The mechanism by which an external electric field induces in an atom a
n electric dipole moment is discussed from classical and quantal point
s of view. It is shown that the expressions for the atomic polarizabil
ity ct derived from each of these viewpoints are, to the same level of
approximation, identical. The classical perspective is, however, more
intuitive and provides a more insightful picture. The presentation is
at the undergraduate level. (C) 1997 American Association of Physics
Teachers.