One of the auxiliary programmes undertaken and nearly completed since the first programme is the determination of the radial velocities of a very interesting but limited class of stars, the highest temperature stars known, the O-type stars. The radial velocities and other interesting data about 50 of these stars have been completed. Spectroscopic Double Stars In the measurement of the radial velocity of the 800 stars on the first programme it was found that in about 180 stars successive plates did not give constant velocities, the stars at one time approaching at another receding from us. This phenomenon is practically certain proof that we are measuring the velocity of a star revolving around an invisible companion and such stars are generally called spectroscopic binaries to distinguish them from visual binaries which can be seen double in the telescope. Over 200 spectroscopic binaries have been discovered at this observatory as compared with about 700 discovered elsewhere, again a considerable addition. In about 20 of these binaries, observations were continued until the period of revolution, the form of the orbit, the separation of the two stars and in some cases, their masses were determined. In a particular class of spectroscopic binaries, the eclipsing variables, which allow from the combination of spectroscopic and photometric measurements the absolute dimensions to be obtained, we were able to determine the separation of the two stars, their diameters, densities, masses and brightnesses and the probable distances. Such complete information has been obtained here about seven systems, while only seven other systems have been determined elsewhere. Absolute Magnitude and Distance A new application of spectroscopic methods is to the determination of the total brightness of the stars as compared with the sun and their distance or “spectroscopic parallax” as it is called. This depends not on the positions but on the relative intensity or strength of the lines in the spectra of the stars and has only been developed in the last three or four years. The absolute magnitude and spectroscopic parallax of about 800 stars is now nearly completed and will soon be published while as a side line the radial velocities of 125 more stars have been determined. Physical Conditions in the Stars