  Following Nye and Berry's analogy with crystal dislocations, an approach to
the Burgers vector of a wave dislocation (phase singularity, optical vortex) is
proposed. It is defined to be a regularized phase gradient evaluated at the
phase singularity, and is computed explicitly. The screw component of this
vector is naturally related to the helicoidal twisting of wavefronts along a
vortex line, and is related to the helicity of the phase gradient. The edge
component is related to the nearby current flow (defined by the phase gradient)
perpendicular to the vortex, and the distribution of this component is found
numerically for random two-dimensional monochromatic waves.
