XXIV 
PRELIMINARY GENERAL CATALOGUE OF STARS FOR 1900 
of the individual components is materially greater than for single stars of the same 
class. Undoubtedly this is largely owing to the inevitable uncertainty of the orbital 
elements adopted in these computations (especially when micrometric observations 
have been extended over a part only of the orbital period); but in an important 
degree, also, uncertainty arises from decidedly individual systematic errors in 
meridian-observations of one component when the other component is distinctly 
visible. Accordingly, the particulars regarding probable error are omitted for these 
stars. At the same time it may be stated that the larger part of these stars, but for 
periodic variability of motion, would have belonged to the higher classes of standards. 
Special computations were made for Groomb 1830 and 61 Cygni for the purpose 
of detecting a foreshortening or perspective effect in the annual motions of these 
stars. In both of these instances the computations seem to have been measurably 
successful in exhibiting such an effect, as will be seen from the detailed notes con¬ 
cerning these stars in Appendix II. In the case of the two components of 61 Cygni, 
the estimated effect of mutual curvature of the components is also included in the 
computation. These effects tend to modify the centennial variations of the proper- 
motions and annual variations; and these centennial variations thus modified are 
adopted in the catalogue-data for these stars. 
As already explained under “Adopted Names,” whenever the letter m is ap¬ 
pended to the name in the second column, it means that the pointing of the observers 
has probably been made either upon the mass of light, or upon the mean when the 
components are either wide or of nearly equal magnitudes. Notes are given in 
some cases; in others there must exist more or less doubt. Usually, however, the 
uncertainty is not very serious, especially where the difference of magnitude is very 
large. 
As a consequence of the discussion that relates to probable corrections required 
for the motion of the equinox and precession adopted in this Catalogue, described 
later under “Proper-motions,” the right-ascensions require a correction of +'.0079 
(r—1850), in consequence of the deduced correction of +"79 to the centennial 
motion of Newcomb’s equinox, N 1? to which the right-ascensions of this Catalogue 
correspond. This correction becomes + ?026 for 1900; and this is the common 
correction of all the right-ascensions of this Catalogue, if it is desired to make them 
correspond to the motion of the equinox so corrected. This probable correction 
receives some support from Newcomb’s discussion of the correction required for 
Ni, so far as it is indicated by the Washington and Greenwich observations for several 
years around 1897. (Ast. Jour., No. 498, Vol. XXI, p. 141.) The following cor¬ 
rections of the equinox, N x , from observations of the sun are there derived: 
From Washington +-°53 1897 
From Greenwich +-005 1896 
The mean of these, +^029, is very near that otherwise found in the foregoing. 
Finally, as will be seen later, it is of the utmost importance that the very great 
differences of accuracy in the catalogue-positions and motions of different stars be 
not overlooked; and especially that due attention be given to the relative degree 
of reliability with which desired predictions for individual stars can be effected. 
