ADVISORY COMMITTEE ON ASTRONOMY 1 23 



This field is important, and much remains to be done. One is 

 tempted to urge that an organized effort be made to revise all the 

 older star catalogues and planetary observations in a manner to 

 render their best results available for the immediate and pressing 

 needs of astronomical investigation. Certainly this work is worthy 

 of aid w-herever it is undertaken upon the initiative of competent 

 hands. 



Determination of Stellar Parallax. 



Closely associated with the work of determining the positions and 

 motions of the stars is the problem of determining their distances 

 through measurement of parallax. Sixty years ago Bessel was the 

 first to measure successfully the parallax of a star, after this problem 

 had baffled the most strenuous efforts of many able astronomers from 

 time to time in the past. Since Bessel's measure of the parallax of 61 

 Cygni other measures have been slowly accumulating, until, within 

 recent years, there has been very greatly increased activity in this 

 line of researches. Parallaxes are measured by many different 

 methods, of which those most approved at present are by means of 

 the heliometer, by means of photography, and by differential tran- 

 sits on the meridian. Gill at the Cape of Good Hope and Elkin at 

 New Haven have determined a large number of parallaxes by meas- 

 urements with a heliometer. Recently Elkin and Chase have been 

 carrying on a kind of parallactic survey upon a very large number 

 of stars. The photographic method has been tried with some de- 

 gree of success by Pritchard of Oxford, and by others. The transit 

 method was first illustrated by Kapteyn, at Leiden, and more re- 

 cently by Flint at Madison (Wis.). Investigators are beginning to 

 realize that the measurement, one by one, of the parallaxes of indi- 

 vidual stars is a task which can no longer be postponed. There is 

 every reason to believe that the photographic method, when applied 

 with the aid of a large telescope of special design, like that proposed 

 at the Yerkes Observatory, may yield results economically and, in 

 all probability, of a high degree of accuracy. 



Variation of Latitude. 



Researches upon this subject have been of great interest ever 

 since Dr. Chandler discovered, a few years ago, that the pole of the 

 earth's figure rotates about the pole of rotation. The consequences 

 of this phenomenon are so interwoven with the determination of the 



