The Calculation of the Convergent of a Moving Cluster of Small Apparent Diameter

The methods of Charlier and Bohlin, for calculating the convergent point of a moving cluster, are discussed and it is shown that a number of different results may be expected from the various possible arrangements of the equations. Examples are given showing that the differences are considerable for groups occupying a limited area on the sky. A method of differential corrections is proposed, more directly related to the observed proper motions, and giving a less ambiguous result for condensed clusters of the Pleiades type.