  The Seebeck effect consists in the induction of a voltage drop due to the
temperature difference in a conductor. In the middle of XIXth century, Lord
Kelvin has proposed a relation between the Seebeck coefficient and the
derivative of the chemical potential over temperature in the broken circuit
regime. This relation appears to be nearly universal as it equally well applies
to metals, semimetals and semiconductors. We show that it may fail, however, in
graphene, due to the non-locality effects in the ballistic electronic transport
regime. The correction to the Kelvin's formula emerges due to the coexistence
of counter-propagating non-dissipative currents of cold and hot electrons. The
external magnetic field normal to the graphene sample allows separating hot and
cold currents in real space. The developed formalism may help interpreting the
recent experimental data on ballistic edge currents in graphene bi-layers in
the quantum Hall regime [1].
