XII 
PRELIMINARY GENERAL CATALOGUE OF STARS FOR 1900 
An account of the methods by which this standard catalogue was constructed, 
in reasonable conformity with the foregoing requirements, is contained in a series 
of papers published in Vol. XXIII of the Astronomical Journal. (Subsequently 
collected and reprinted under the title: Catalogue of 627 Principal Standard Stars.) 
The successive approximations required in extending the number of stars contained 
in the Standard Catalogue, the estimate of value of each catalogue of observation as 
an original, or independent, source of determination, and the devices employed in 
the treatment of individual catalogues and in the combination of one with another, 
are there set forth, probably in sufficient detail to permit the formation of an inde¬ 
pendent judgment as to the character of the result. In much the same way the 
arrangement in chronological order of the systematic corrections of Appendix III 
(this volume) zone by zone will afford a rough means of estimating whether the 
system of the standard sufficiently well represents at various epochs the catalogues 
having value as independent sources of knowledge as to star positions. 
In this connection, however, it should be noted that this method will not give 
reliable information as to an effect upon the stars of an incorrectly assumed motion 
of the equinox. This requires a special investigation. In the present work the 
equinox determined in 1872 by Professor Newcomb has been adopted. (See: On 
the Right-Ascensions of the Equatorial Fundamental Stars, by Simon Newcomb, 
Washington Observations, 1870.) This probably requires material revision; but 
any such revision would affect all the proper-motions in right-ascension by a 
constant quantity. 
Furthermore, it should also be noted, as to the declinations, that pairs of con¬ 
temporaneous catalogues, one emanating from an observatory in the Northern and 
the other from an observatory in the Southern hemisphere, have been treated 
together in the present investigation for mutual correction of their results, previously 
to their introduction into the formation of the Standard Catalogue. Such pairs 
were formed, for example, from Camb 30 and Cape 33, Grw 60 and Cape 6o, Grw 64 
and Melb 70, and from many others suitable to the purpose. The comparison of 
the members of these pairs gave rise to equations for the determination of correc¬ 
tions to the refractions adopted in the reduction of the respective catalogues. It 
may well be urged that no series of determinations of star-declinations can be criti¬ 
cally regarded as sufficiently independent that rests upon a system of refraction- 
corrections determined at another observatory, for another horizon and for another 
exposure of the thermometer. But in spite of certain technical objections, it can 
scarcely be contended that the combination of contemporaneous results from north¬ 
ern and southern observatories in pairs {Ast. Jour., 540; also Declination of 500 
Stars, Boss) in the manner and for the purpose herein indicated, results otherwise 
than in a very decided increase in the value of each of the catalogues as sources of 
absolute determination of star-declinations. 
The preparation of the Catalogue 0/627 Principal Standard Stars was only the 
foundation structure in a process that has since been continued and elaborated. 
It may be well to remark here, that the utmost circumspection was required during 
these successive enlargements of the Standard Catalogue that, in the positions of the 
stars successively added to it as secondary standards, the original system should be 
