  We outline a conventional path integral derivation of the transverse force
and the friction for a vortex in a superconductor based on the BCS theory. The
derivation is valid in both clean and dirty limits at both zero and finite
temperatures. The transverse force is found to be precisely as what has been
obtained by Ao and Thouless using the Berry's phase method. The friction is
essentially the same as the Bardeen and Stephen's result.
  Errors in some previous representive microscopic derivations are discussed.
