206 REPORTS ON INVEISTIGATIONS AND PROJECTS. 



But aside from considerations of classification, large numbers of objects 

 are desirable in order to eliminate the purely fortuitous elements of motion. 

 In the attempt to secure the effect of pure parallactic motion of the stars in 

 any selected area of sky, the number of stars required to practically elimi- 

 nate accidental errors in the data of computation is small in comparison 

 with that which is required for effective elimination of the effects of ran- 

 dom motion, complicated as it is by numerous instances of star-drift in 

 various localities all over the sky. 



Our work necessarily includes not only research upon, and assimilation 

 of, results of observation in the past, but also a strong contribution of 

 observations now. Other things being equal in measuring motions, obser- 

 vations at the two extremes of the interval in time — the oldest and the 

 latest — are the most valuable. Therefore, reobservation of stars most in 

 need of redetermination at the present time forms an important feature of 

 our program. 



Early in the progress of the work now going on at the Dudley Observa- 

 tory it was seen that the most important obstacle to successful prosecution 

 of work in deriving motion for the stars lay in the difficulty of computing 

 such motion with sufficient accuracy for the southernmost one-fourth of the 

 sky. This difficulty can be remedied only through further observations. 



The distinctive feature of the further work as now authorized is found 

 in the project for meridian observation of the stars of the southern hemi- 

 sphere not accessible to exact observation at observatories in the northern 

 hemisphere. To carry out this part of the program provision has been 

 made to transport to some suitable site in the southern hemisphere the 

 meridian circle belonging to the Dudley Observatory. The trustees of the 

 Dudley Observatory, at their annual meeting of the present year, formally 

 sanctioned this proposed use of the instrument, and in other respects have 

 placed the resources of the observatory at the disposal of this Department 

 of Meridian Astrometry. 



The use of this meridian-circle alternately in the two hemispheres is 

 designed to take advantage of the combination of observations made at 

 Albany with those to be made at the selected southern station with a view 

 to securing greater accuracy in the systematic, or fundamental, sense. The 

 plan is to continue fundamental observations here until some time in 1908, 

 then to set up the instrument at a southern station to be occupied for about 

 three years, and, again returning the instrument to Albany, to complete the 

 corresponding series of observations here. The distance from the north to 

 the south pole being, necessarily, exactly 180°, it follows that if the minute 

 systematic errors of measurement of the instrument remain the same for its 

 use in the two hemispheres they will precisely eliminate for observations at 

 or near the equator. Nor will it be necessary to assume that the law of 

 atmospheric refraction is the same at the two stations. A proper arrange- 



