2 PROCEEDINGS OF THE AMERICAN ACADEMY 



choice ; but the attempt is made to avoid needless duplication of the 

 work of others. A previous series of right ascensions, which I ob- 

 served in 1862-G6 at Cambridge, was not found superfluous. 



Both then and now I have been impressed with certain deficiencies 

 in our fundamental catalogues, as, indeed, have other astronomers. 

 These deficiencies are not the fault of those who have constructed the 

 catalogues, but arise from the lack of foresight in the astronomers 

 of the last century. Our fundamental and secondary places are 

 perfectly good and sure, taken as a whole, for 1865 or thereabouts ; 

 but in many cases accurate proper motions are lacking to bring thera 

 up to the present epoch. Stars which Bradley observed with suffi- 

 cient completeness about 1755 can be accurately brought up by 

 proper motions derived from his observations. 



But Bradley could not foresee what observers would need a century 

 or more after his decease ; and omitted to provide us all the materials 

 we now need, especially in this polar region. The next set of ob- 

 servers — Piazzi, Groombridge, etc. — did not emploj^ stellar observa- 

 tions for the correction of their instruments, but meridian marks ; and 

 depended upon occasional adjustments, overlooking the tendency now 

 so well known of instruments to crawl away from their adjustments 

 through molecular strains connected with change of temperature. 

 Consequently, when Bradley, 1755, fails us, the observations of Struve, 

 beginning in 1814, are the first which really come up to Bradley's 

 standard. 



So that in my use of the best fundamental catalogue now existing, 

 that of the Astronomische Gesellschaft, I have thought it safest to 

 begin by excluding for instrumental corrections all stars whose proper 

 motions do not essentially depend upon Bradley, or upon Struve and 

 later observers. This excludes quite a number of the right ascensions 

 even of the Hauptsterne ; as well those whose errors Professor Rogers 

 and Mr. Chandler have detected, as those which, equally uncertain 

 a pi'iori, are approximately con-ect by compensation of errors. In 

 their plac^ I have substituted a number of closer polars whose right 

 ascensions are thoroughly well determined by modern observations, 

 and whose proper motions are also accurately known. In collecting 

 modern observations, my own Harvard catalogue of 1865, and the 

 work since done there by Professor Rogers, as well as the Williams- 

 town observations, have been added to the ordinary catalogues ; and 

 I have sought out and reduced the single Pulcova observations 

 made in this region by Winnecke and Gromadski between 1858 and 

 1869. 



