Approximate Calculation of the Anisotropy of the Relaxation Time of the Conduction Electrons in the Noble Metals

The ratio of the relaxation times on the "belly" and on the "necks" of the Fermi surface is estimated numerically by very crude methods. It is shown that the relative amount of $s$-wave to $p$-wave scattering by impurities is important and that Umklapp processes play a major role in phonon scattering. The ratio depends on impurity type and on temperature in just the right way to explain qualitatively the variation of the Hall coefficient in the metals and their alloys.