Number 133 (Story #3), June 17, 1993 by Phillip F. Schewe and Ben Stein THE LARGE MAGELLANIC CLOUD orbits the Milky Way with a transverse speed of 220 km/sec. With photos of the LMC (and its attendant stream of hydrogen gas streaming behind) taken 15 years apart, Douglas Lin of UC Santa Cruz not only calculates the satellite galaxy's speed (the first time another galaxy's motion across the sky has been measured) but also arrives at a rough estimate of the distribution and density of matter (including dark matter) in the Milky Way needed to produce such a motion. (Science News, 12 June, reporting on last week's Berkeley meeting of the American Astronomical Society.)