  Cryogenic cluster beam experiments have provided crucial insights into the
evolution of the metallic state from the atom to the bulk. Surprisingly, one of
the most fundamental metallic properties, the ability of a metal to efficiently
screen electric fields, is still poorly understood in small clusters. Theory
has predicted that many small Na clusters are unable to screen charge
inhomogeneities and thus have permanent dipole moments. High precision electric
deflection experiments on cryogenically cooled Na$_N$ ($N<200$) clusters show
that the electric dipole moments are at least an order of magnitude smaller
than predicted, and are consistent with zero, as expected for a metal. The
polarizabilities of Na clusters also show metal spheroid behavior, with fine
size oscillations caused by the shell structure.
