PROBLEMS IN ASTROPHYSICS 469 



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 centres 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 hemi- 

 sphere, 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 ex- 

 peditionary 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 con- 

 fusion. 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 initia- 

 tive. 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. 



