Page:Catalogue of 1068 "intermediate" stars.djvu/7



the International Astrographic Congress, held in Paris in 1909, it was resolved that three lists of Stars, viz., Fundamental, Intermediate, and Reference, should be prepared, and that transit observers should be requested to make these, as far as practicable, the bases of their working catalogues. It was intended that the Intermediate and Reference Stars should be observed by differential methods, the former being used as standards for the latter, and in their turn depending upon the Fundamentals. Meridian observations based upon this principle were commenced at the Sydney Observatory on 11th March, 1918, the first selection of stars being the list of Intermediates between 51° and 65° South declination, supplied in manuscript by the sub-committee of the Astrographic Congress; and the present catalogue gives the results of those observations. This list was accepted as a working catalogue, but it was found necessary, or at least advisable, to modify it to a considerable extent. I felt justified in doing this, because I believe the Sydney Observatory is the first to form a catalogue of this particular series of stars, and therefore any alterations will not affect other workers in the same field. I hope therefore that the list, as now amended, will be generally accepted.

The principle of making the catalogued positions depend upon those of the Fundamental Stars within the same region has been applied more rigidly than hitherto. A full description of the methods of observing and computing is given in the "Monthly Notices, R.A.S.," LXXIX, No. I, November, 1918. As these differ radically from those in general use it is requested that any astronomers who are specially interested in the accuracy of this catalogue will read the above-mentioned article. Briefly, observations are limited entirely to stars within the zone 5i-65, and special observations for level and azimuth errors are eliminated. All necessary instrumental errors (except collimation) are deduced in a manner analogous to that employed in the computation of astrographic plate constants. That is to say, that after the application of differential star reductions for precession, &c., the observed transit is subject to a correction of the form

where a = tan δ, t = time elapsed since some adopted whole hour, y = clock rate. The quantities x, y, and Z are determined from the Fundamental