  Velocity fields can be reconstructed at cosmological scales from their
influence on the correlation between the cosmic microwave background and
large-scale structure. Effects that induce such correlations include the
kinetic Sunyaev Zel'dovich (kSZ) effect and the moving-lens effect, both of
which will be measured to high precision with upcoming cosmology experiments.
Galaxy measurements also provide a window into measuring velocities from the
effect of redshift-space distortions (RSDs). The information that can be
accessed from the kSZ or RSDs, however, is limited by astrophysical
uncertainties and systematic effects, which may significantly reduce our
ability to constrain cosmological parameters such as $f\sigma_8$. In this
paper, we show how the large-scale transverse-velocity field, which can be
reconstructed from measurements of the moving-lens effect, can be used to
measure $f\sigma_8$ to high precision.
