bright star with the Mills spectrograph. The method promises to be of great utility, capable of application to several thousand stars between the fifth and eighth magnitudes.
On account of the large proportion of spectroscopic binaries, stars should not be used statistically until observations covering several years have established the constancy of their motions. To determine the orbits and the speeds of the centers of mass of the binary systems, from twenty-five or more spectrograms each, is a task several fold more extensive than that of measuring the constant speeds of the non-binary stars.
There remains the question of cooperation, on the part of radial-velocity observers, to avoid useless duplication, and to increase the output of results. Seven leading observatories in the northern hemisphere, and one in the southern, are in this field, presumably with the intention of remaining indefinitely. A second observatory in the southern hemisphere, devoted exclusively to this work, is of an expeditionary character, and its long continuance is problematical. It is fair to the participating observatories to say, judging by results thus far published, that some are still in the period of experiment and development; and, in fact, that all observers are introducing frequent improvements, which lead to greater accuracy. As long as the development of instruments and methods is in rapid progress, formal cooperation is unwise. Premature cooperation leads to confusion. Duplication of observations for the principal stars is as valuable and desirable in radial-velocity measurements as in meridian determinations of stellar positions. But just as soon as the methods assume a reasonably stable form, the entire sky should be apportioned amongst the interested observatories, in accordance with carefully considered plans which shall permit and encourage individual initiative. I have little doubt that this point will be reached, by a sufficient number of observatories, within two years, and that it would be well to conclude the preliminary organization of cooperative plans within the coming year. Such plans should be formed with severe deliberation, as the labor involved would be commensurate with that devoted to the construction of the Astronomische Gesellschaft Zones for the entire sky.
The problems immediately confronting the astrophysicists of the twentieth century are serious ones. They call for our best efforts. The volume of work demanded is stupendous, and the difficulties to be overcome are correspondingly great. Nevertheless, the men and the means will be forthcoming. The mass of solid fact brought within the realm of knowledge by astronomers now living, many of whom are happily with us this week, is sufficient indication that the general solution of the problems of to-day is but a question of time. And we should be equally hopeful as to the problems of the future, for the desire to know the truth about the universe which surrounds us is an enduring element in human nature.
