28 



GOULD REDUCTION OP D AGELET S OBSERVATIONS. 



The arrangement of the catalogue requires little comment. After the running numbers 

 for reference, which have been so arranged as to avoid separating different observations of the 

 same star, the second column contains the names. These are not those recorded by d'Agelet, 

 but are those obtained by identification of the stars. So far as possible, Flamsteed's numbers 

 and Bayer's letters have been given; and in default of these, the reference-numbers from 

 Mayer's, Bradley's (Bessel's) Piazzi's, and other standard catalogues, in order of seniority. 

 But since an easy recognition, rather than a systematic nomenclature, has been aimed at, this rule 

 may sometimes have been inadvertently violated. The references for Flamsteed' s, Lacaille's, 

 and Lalande's observations are to their numbers in Baily's reductions; those for Bessel's ami 

 Argelander's zones, to the respective numbers in Weisse's and Oeltzen's reductions, as is 

 also indicated by the appended initials. 



The magnitudes are those recorded by d'Agelet, and are omitted when not given by him. 

 In the column "date" the year is indicated by its last digit, thus: 3, 4, 5, instead of 1783, 

 1784, 1785. The columns " reduction" contain the reduction from the apparent equinox of 

 date to the mean equinox of 1800.0. 



§ 12. ACCURACY OF THE RESULTS. 



The catalogue contains 0,497 observations of 2,907 stars; so that the average number of 

 observations for each star is about 2£. Actually, 38 stars were observed more than ten times; 

 G5 from seven to ten times, inclusive; 140 five or six times; 183 four times; 33G three times; 

 740 twice; and 1405 only once. 



A comparison of the several positions of each star with each other, or with their mean, 

 affords an opportunity for estimating the precision of the results ; and from discussion of the 

 several determinations of all those stars which have been observed more than three times we 

 derive the following values for the mean deviations from the mean: 



Mean error of a single observation. 



(28) 



