The thermoelectric power of the alkali metals at low temperatures

The effect of phonon drag is calculated, taking account of electron-phonon Umklapp processes, and anisotropy of the Fermi surface. For Na, the observations are perfectly fitted with a spherical surface. For K, Rb and Cs, the surfaces must bulge more than half way towards the faces of the Brillouin zone, whilst in Li it probably touches the zone boundary.