A detailed comparison is presented of the temperature dependence of the
conductivity of dilute, strongly interacting electrons in two-dimensional
silicon inversion layers in the metallic regime in the presence and in the
absence of a magnetic field. We show explicitly and quantitatively that a
magnetic field applied parallel to the plane of the electrons reduces the slope
of the conductivity versus temperature curves to near zero over a broad range
of electron densities extending from nc to deep in the metallic regime where
the high field conductivity is on the order of 10e2/h. The strong
suppression (or "quenching") of the metallic behavior by a magnetic field sets
an important constraint on theory.Comment: 4 pages, 4 figure