IV 
PRELIMINARY GENERAL CATALOGUE OF STARS FOR 19OO 
aiming to compute accurate values of proper-motions for a very large number 
of stars might be the ascertainment of the systematic corrections required by the 
various star-catalogues. This will readily appear upon consultation of the Tables 
of Systematic Corrections, in Appendix III of this volume. This correction is 
especially marked for Bradley’s declinations, hitherto a very important element in 
the derivation of proper-motions. For large areas of sky south of + 40° of dec¬ 
lination, centennial proper-motions in declination computed by means of uncorrected 
declinations of Bradley-Auwers compared with perfect declinations 100 years 
later would systematically differ from the corresponding quantities printed in the 
present work by i'.'5, or more; and in the zone -I- 34 0 to + 38° by 2" or more. 
While this may be an extreme illustration it serves to indicate the nature of possible 
effects due to the application of systematic corrections to the positions contained 
in the catalogues. It becomes obvious that when we are dealing with the smaller 
proper-motions the elucidation of the amount and direction of residual-stardrift 
in various parts of the sky may be dependent upon the systematic errors of the 
star-catalogue in a very important degree. Governed by these and other consider¬ 
ations, the author decided to alter the original plan of reluctantly confining his 
attention to stars having only comparatively large proper-motions, and, as the 
indispensable preliminary to his work, to institute a thorough inquiry as to the 
systematic corrections required by the various catalogues of observation in order 
to make each so far as possible systematically conformable with the combined 
result from all. 
It is not necessary here to trace the various steps in these operations. It is 
sufficient to say that the plan involved the preparation of an extensive catalogue of 
standard stars. The close of an important stage of this work was marked by the 
publication of the Catalogue of 627 Principal Standard Stars, together with various 
chapters explaining the methods employed in the construction of that catalogue and 
exhibiting, also, the systematic corrections required by the various star-catalogues 
in order to bring them into conformity with this new system. ( Ast . Jour., Vol. 
XXIII.) These articles were also reprinted in a separate publication entitled, 
“Catalogue of 627 Principal Standard Stars P The systematic corrections there 
published have since been subjected to thorough revision on the basis of a greatly 
extended list of </mm’-standard -stars; but, fundamentally, there has been no 
sensible alteration of the general system. 
From the beginning of this work it had been assumed to be quite as important 
that we should know the motions of stars in the Southern hemisphere as in the North¬ 
ern. It would, therefore, be important for ascertaining systematic corrections not 
only that there should be formed a new and very extensive catalogue of standard 
stars, distributed over the entire sky from pole to pole, but also that the positions 
should form a consistent and homogeneous system derived from careful considera¬ 
tion of all suitable observations — southern as well as northern. This catalogue 
would have to be extensive, because it would be impossible to ascertain properly 
the systematic corrections required for the larger catalogues — like Arm 40, 
Radcl 45, Bruss 65, Cord 75, Cape 80, etc. — without a much larger number of 
comparisons with standard stars than had been available with the existing catalogues 
