During the past three years the measurement of stellar radial velocities has formed an important part of the spectroscopic programme of most observatories possessing large telescopes. As observations are carried to fainter and fainter stars and the number of observable objects increases rapidly, a natural development has been the selection of special groups and types of stars, the radial velocities of which will aid in the solution of certain specific problems. Illustrations are the studies of the O, B and A type stars made at the Dominion Astrophysical, the Lick, and the Simeis Observatories, of the members of the galactic clusters at the Lick Observatory, and of the fainter Cepheid variables and early-type stars with strong interstellar lines at the Mount Wilson Observatory.
Radial velocities of early-type stars in the Perseus OB2 association