  The frequency spectrum of the finite temperature correction to the Casimir
force can be determined by use of the Lifshitz formalism for metallic plates of
finite conductivity. We show that the correction for the $TE$ electromagnetic
modes is dominated by frequencies so low that the plates cannot be modelled as
ideal dielectrics. We also address issues relating to the behavior of
electromagnetic fields at the surfaces and within metallic conductors, and
calculate the surface modes using appropriate low-frequency metallic boundary
conditions. Our result brings the thermal correction into agreement with
experimental results that were previously obtained. We suggest a series of
measurements that will test the veracity of our analysis.
