398 THE NEW WORLD OF SCIENCE 



seem on first examination to be slight, it nevertheless involves 

 a fundamental question of principle, so important that it calls 

 for special emphasis in any discussion of cooperative research. 

 One of the great problems of astronomy is the determination 

 of the structure of the sidereal universe. Its complete solution 

 would involve countless observations. Nevertheless, Professor 

 Kapteyn, the eminent Dutch astronomer, resolved many years 

 ago to make a serious effort to deal with the question. In order 

 to do so, as he had no telescope or other observational means 

 of his own, he enlisted the cooperation of astronomers scattered 

 over the whole world. 



In organizing his attack, he recognized that the inclusion of 

 only the brighter stars, or even of all those contained in the 

 International Chart of the Heavens, would not nearly suffice 

 for his purpose. He must penetrate as far as possible into the 

 depths of space, and, therefore, thousands of millions of stars 

 are of direct importance in his studies. Moreover, it is evident 

 that if he were to confine his attention to some limited region 

 of the sky, he could form no conclusion regarding the distribu- 

 tion of stars in other directions in space or such common 

 motions as might be shown, for example, by immense streams 

 of stars circling about the center of the visible universe. 



As the measurement of the positions, the motions, the bright- 

 ness, and the distances of all the stars within the reach of the 

 most powerful telescopes would be a truly Utopian task, Pro- 

 fessor Kapteyn wisely limited his efforts, and at the same time 

 provided a means of obtaining the uniformly distributed obser- 

 vations essential to the discussion of his great problem. His 

 simple plan was to divide the entire sky into a series of 206 

 Selected Areas, thus providing sample regions, uniformly spaced 

 and regularly distributed over the entire celestial sphere. Con- 

 clusions based upon the observation of stars in these areas are 

 almost as reliable, so far as large general questions of structure 

 and motion are concerned, as though data were available for all 

 the stars of the visible sidereal universe. 



As already remarked, Professor Kapteyn depends entirely 



