  The dynamics of the deformations of a moving contact line is studied assuming
two different dissipation mechanisms. It is shown that the characteristic
relaxation time for a deformation of wavelength $2\pi/|k|$ of a contact line
moving with velocity $v$ is given as $\tau^{-1}(k)=c(v) |k|$. The velocity
dependence of $c(v)$ is shown to drastically depend on the dissipation
mechanism: we find $c(v)=c(v=0)-2 v$ for the case when the dynamics is governed
by microscopic jumps of single molecules at the tip (Blake mechanism), and
$c(v)\simeq c(v=0)-4 v$ when viscous hydrodynamic losses inside the moving
liquid wedge dominate (de Gennes mechanism). We thus suggest that the debated
dominant dissipation mechanism can be experimentally determined using
relaxation measurements similar to the Ondarcuhu-Veyssie experiment [T.
Ondarcuhu and M. Veyssie, Nature {\bf 352}, 418 (1991)].
