THE SEMI-CENTENNIAL ANNIVERSARY 23 



unless it is effectively impressed on their attention by some per- 

 manent body. Where to find such a central body, whose main 

 functions would be to endow an undertaking with sufficient 

 inertia to carry it over periods in which the work may seem to be 

 a drudgery, is a matter which deserves careful consideration. 



The completion of the Star Catalogue, which has given rise 

 to these remarks, is only the beginning of an even greater piece 

 of work. When we have determined the positions and magni- 

 tude of stars at any one time, we have only taken the first step 

 towards solving the main problem, and must proceed to measure 

 the proper motions, the parallaxes, and also map the spectra. 

 This work is so vast that all hope to accomplish it within reason- 

 able limits is difficult and has to be abandoned unless our statis- 

 tical ambitions are lowered, and instead of taking the complete 

 sphere of the heavens we select restricted but typical areas for 

 detailed examination. This has been done on the initiative of 

 Professor Kapteyn, who has secured a sufficient number of 

 voluntary associates who are now carrying out a combined 

 undertaking which has already yielded results of the greatest 

 importance, and you will hear something more of this work from 

 his own lips. 



Now the essence of work of this kind consists in shortening 

 the time required to accomplish an extensive task by dividing it 

 among a number of persons. If the work is purely statistical, it 

 may be complete in itself, and the published records become then 

 available to anyone who requires them. In other cases, the ob- 

 servations may have to be collected by a central authority and 

 treated by recognized methods of statistics or analysis before 

 they become useful to the scientific public. While it is gener- 

 ally the observational portion of the work that is subdivided and 

 the discussion that is centralized, the reverse is the case in the 

 proposal made by Professor Pickering that one central observ- 

 atory in a favorable position should furnish photographs in 

 sufficient numbers and distribute them among astronomers all 

 over the world, to be measured and discussed. 



