  We develop a theory of transverse thermoelectric (Peltier) conductivity,
\alpha_{xy}, in finite magnetic field -- this particular conductivity is often
the most important contribution to the Nernst thermopower. We demonstrate that
\alpha_{xy} of a free electron gas can be expressed purely and exactly as the
entropy per carrier irrespective of temperature (which agrees with seminal Hall
bar result of Girvin and Jonson). In two dimensions we prove the universality
of this result in the presence of disorder which allows explicit demonstration
of a number features of interest to experiments on graphene and other
two-dimensional materials. We also exploit this relationship in the low field
regime and to analyze the rich singularity structure in \alpha_{xy}(B, T) in
three dimensions; we discuss its possible experimental implications.
