The Ursa Major Group.

The Ursa Major group is investigated in detail. It is shown that a small, compact cluster can be dis- tinguished from the large, ill-defined stream. An introduction to the problem is given in Section I. Sec- tion II contains a summary of the previous work on the group, together with a bibliography. In Section III the position of the convergent point is determined from the proper motions of the nucleus stars. It is shown that these proper motions determine the position of this point quite accurately. New mea surements of the radial velocities of the brighter nucleus stars are discussed in Section IV and are used to determine the space velocity of the cluster. The results indicate that a velocity may be found which agrees with the individual parallaxes and radial velocities within their expected uncertainty, but the systematic differ- ences between the results from these two sets of data cannot be completely removed. In SectionV, the results of a search for new members within 20 parsecs of the center of the nucleus are described. A list of members and a description of the cluster are given. Section VI contains a list of all stars which have been assigned to the Ursa Major stream and compares the observed and the computed data for these stars. New spectral types and spectroscopic absolute magnitudes are given for those stars for which the agree- ment between the observed and the computed data is best and which are north of declination _300. Sec- tion VII summarizes the results of the investigation