  A thermal gradient generates an electric field in any solid hosting mobile
electrons. In presence of a finite magnetic field (or Berry curvature) this
electric field has a transverse component. These are known as Seebeck and
Nernst coefficients. As Callen argued, back in 1948, the Seebeck effect
quantifies the entropy carried by a flow of charged particles in absence of
thermal gradient. Similarly, the Nernst conductivity, $\alpha_{xy}$, quantifies
the entropy carried by a flow of magnetic flux in absence of thermal gradient.
The present paper summarizes a picture in which the rough amplitude of the
thermoelectric response is given by fundamental units and material-dependent
length scales. Therefore, knowledge of material-dependent length scales allows
predicting the amplitude of the signal measured by experiments. Specifically,
the Nernst conductivity scales with the square of the mean-free-path in metals.
Its anomalous component in magnets scales with the square of the fictitious
magnetic length. Ephemeral Cooper pairs in the normal state of a superconductor
generate a signal, which scales with the square of the superconducting
coherence length and smoothly evolves to the signal produced by mobile vortices
below the critical temperature.
