  The dark matter distribution of the Milky Way remains among the major
unsolved problems about our home galaxy. The masses of other spiral galaxies
can be determined from their rotation curves through long-slit spectroscopy.
But for the Milky Way obtaining the complete rotation curve is a more complex
problem. By measuring the 3-dimensional motions of tracer objects the rotation
curve and Galactic mass distribution can be derived, even outside the solar
circle where HI tangent point analysis is not possible. We present the first
findings from a project to measure the motions of open clusters, both inside
and outside the solar circle. From a nearly uniform sample of spectroscopic
data for large numbers of stars in over 50 open clusters in the third and
fourth Galactic quadrants, we derive the speed of Galactic rotation at the
solar circle as $\Theta_0 = 214^{+6}_{-9}$ km s$^{-1}$. Future work will
include clusters in the other Galactic quadrants and analysis of the local
rotation curve.
