It is shown that the roton-limited mobility varies with temperature as
<(sigma)over bar>(r)e(-Delta/kBT) where <(sigma)over bar>(r) is the r
oton scattering cross-section and a is the roton minimum. The theoreti
cal phonon-and roton-limited mobilities are in good agreement with the
experimental data for the temperature ranges from similar to 0.02 K t
o similar to 0.12 K and from similar to 1.0 K-1 to similar to 1.85 K-1
, respectively.