Investigations on Proper Motion. Twenty-Second Paper: the Proper Motion of the Open Cluster Messier 67.
On two pairs of plates of Messier 67 taken at the Cassegrain focus of the 60-inch reflector with an interval of 21 years, 343 stars were measured for proper motion. The probable error of a final motion in each co-ordinate is, in the mean, O'~OOO8. The 284 stars probably belonging to the cluster give, as a final relative motion with respect to the stars of mean magnitude 14.5: = -O~OO46; p~ = +O~OOO3