  The shear viscosity of a two-dimensional liquid-state dusty plasma was
measured experimentally. A monolayer of highly charged polymer microspheres,
with a Yukawa interaction, was suspended in a plasma sheath. Two
counter-propagating Ar laser beams pushed the particles, causing shear-induced
melting of the monolayer and a shear flow in a planar Couette configuration. By
fitting the particle velocity profiles in the shear flow to a Navier-Stokes
model, the kinematic viscosity was calculated; it was of order 1 mm^2/s,
depending on the monolayer's parameters and shear stress applied.
