  There is intense interest in determining the precise contribution of
Alfv\'enic waves propagating along solar structures to the problems of coronal
heating and solar wind acceleration. Since the launch of SDO/AIA, it has been
possible to resolve transverse oscillations in off-limb solar polar plumes and
recently McIntosh et al. (2011, Nature, 475, 477) concluded that such waves are
energetic enough to play a role in heating the corona and accelerating the fast
solar wind. However, this result is based on comparisons to Monte Carlo
simulations and confirmation via direct measurements is still outstanding.
Thus, this letter reports on the first direct measurements of transverse wave
motions in solar polar plumes. Over a 4 hour period, we measure the transverse
displacements, periods and velocity amplitudes of 596 distinct oscillations
observed in the 171 \AA channel of SDO/AIA. We find a broad range of
non-uniformly distributed parameter values which are well described by
log-normal distributions with peaks at $234$ km, $121$ s and $8$ km s$^{-1}$,
and mean and standard deviations of $407\pm297$ km, $173\pm118$ s and $14\pm10$
km s$^{-1}$. Within standard deviations, our direct measurements are broadly
consistent with previous results. However, accounting for the whole of our
observed non-uniform parameter distribution we calculate an energy flux of
$9-24$ W m$^{-2}$, which is $4-10$ times below the energy requirement for solar
wind acceleration. Hence, our results indicate that transverse MHD waves as
resolved by SDO/AIA cannot be the dominant energy source for fast solar wind
acceleration in the open-field corona.
