GOULD REDUCTION OF d'aGELET's OBSERVATIONS. 



29 



Of the 2907 stars of this catalogue, 274 occur in Argelander' s Positiones Media ; and a 

 comparison of their several places as here given, with those derived from Argelander' s cata- 

 logue, using his precession and proper-motion excepting for our standard stars, but making 

 the slight corrections requisite for reducing to Peters's nutation, furnishes the anuexed 

 results for the mean values of the difference of Argelander — d'Agelet, after rejecting 12 

 cases in R. A., and G in Declination. The average discordances are the means of the differ- 

 ences, disregarding signs. 



The resultant differences Argelaxder — d'Agelet are — 



A a = + Os.015 by 262 stars ; A ri = — 0".070 by 268 stars ; 



= + .013 by 990 observations ; = + .098 by 1,055 observations. 



Similarly a comparison of more than 1800 stars common to this catalogue and the second 

 catalogue of Piazzi has yielded the following results, after applying the proper-motion for seven- 

 teen years to the places of those few stars for which its existence and amount are well established, 

 and rejecting 31 cases. Inasmuch as Piazzi's observations extended over the whole interval 

 between 1792 and 1813, and the dates of the observations can only be deduced from the Storia 

 Celeste by dint of great labor, this approximation has seemed to me sufficient; and although 

 the residual discordances must somewhat exceed the true differences obtainable by the use of 

 better values of the proper-motion than were at Piazzi's disposal, still the errors thus incurred 

 will be very small, and for the most part susceptible of elimination. 



It became manifest from the first that the differences of the two catalogues, especially in 



declination, varied greatly with the right-ascensions, and that the dividing lines between two 



distinct groups were not very remote from the equinoctial colures. In the appended table of 



comparisons. I have assorted the differences Piazzi — d'Agelet, for each zone of declination in 



two groups, bounded by even hours of right-ascension, arbitrarily selected. The discrepancies 



do not appear to be chiefly due to the apparent proper-motions occasioned by the motion of 



our system, although this vera causa must exert an influence; but they are apparently the 



result of intrinsic peculiarity of Piazzi's catalogue. 



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