102 41 32 Lalande, 8880; Schjellerup, 1508-9; Armagh,, 580. Lalande, 8575; Schjellerup, 1449. Lalande, 8745-6; Arg.-Oeltzen, 3220–1. Equatoreal. Star. N.P.D. h m 8 I 5 14 22.61 4 36 40'24 Equatoreal. Arg.-Oeltzen, 2842; Cincinnati Zone, 579. 109 17 8.5 Lalande, 7815; Cincinnati Zone, 584; Armagh,, 516. 109 34 127 Arg.-Oeltzen, 2861; Cincinnati Zone, 112 36 00 117 21 494 583. Lalande, 7298; Cincinnati Zone, 542. Lalande, 7311; Cincinnati Zone, 543. 119 20 109 Arg.-Oeltzen, 1951; Brussels, 1165; Yarnall, 1375; Brussels, 1228; Cordoba Zone, 73.136. Greenwich Cat., 1880'484; Stone, 1317 119 39 462 Arg.-Oeltzen, 2006; Cordoba Zone, 73.123. I 20 8 105 Arg.-Oeltzen, 1970; Cordoba Zone, 73'120. 120 16 302 Arg.-Oeltzen, 1881; Cordoba Zone, 73.109. 120 16 536 Arg.-Oeltzen, 1899-1900; Cordoba Zone, 73.110. Galactic Longitudes and Latitudes of the brighter Stars in a Zone of the Heavens containing the Milky Way. By A. Marth. In a paper communicated, twenty years ago, to the Royal Astronomical Society by Mr. Lassell, and published in vol. xxxiii. of the Monthly Notices (pp. 1-14 and 517-527), with a supplement published in vol. xxxiv. (pp. 77-82), I supplied the galactic co-ordinates of the leading stars within or near the Milky Way, so that they might serve as a correct groundwork for representations of the Galaxy, for which an appeal was made to competent draughtsmen. At that time the only accessible modern delineation of the Milky Way derived directly from the sky was that of the southern portion from Antinous to Monoceros, found on plate xiii. of Sir John Herschel's Results of Astronomical Observations made at the Cape of Good Hope. As explained in article (341) of the volume, Herschel had made his original drawings on a larger scale on blank paper on which he had pricked off the stars from Bode's charts. Adopting for his general map the projection, in which the galactic circle or the medial line of the entire Galaxy is extended into a straight line, he had then laid down " (from a good celestial globe, by Bardin, for 1800) the chief stars as a skeleton-inserting others from the maps by the aid of proportional compasses," and had worked over it an accurate resemblance of the forms and, as near as possible, of the intensities of the several parts of the Milky Way as represented in the original drawings. Whatever device may have been used in transferring the positions of the chief stars from the globe to the sheet of paper, the introduction of some sensible inaccuracies in fixing the positions in that way could not well be avoided, and it was with the view of sparing intending draughtsmen all such preliminary trouble, and of insuring the correct positions of the stars, that I prepared the former list of co-ordinates, in the hope that competent observers would take advantage of the means thus provided. A few years later I was informed by Mr. Trouvelot, then at Cambridge, Mass., that he had adopted the data of the list as the foundation of a pastel drawing of the Galaxy, which was being exhibited at the Philadelphia Exhibition of 1876, and that it was under consideration how to get it published. As I had not heard since what had become of the publication, I wrote last May to Mr. Trouvelot, now at Meudon, to inquire, and he was good enough not only to give me the desired information, but also to send me, with some smaller photographs, a print (white on black) of the one-half of his drawing which has been published by Charles Scribner's Sons, of New York, in their series of astronomical drawings. This print is now in the library of the Royal Astronomical Society, to which, by leave and in the name of Mr. Trouvelot, I have transferred it. An extract from his letter will best explain several peculiarities of the print: "The list of co-ordinates of stars which you published served as basis for the drawing. But in order to make a picture, the vacant spaces were filled in with stars borrowed from Dien's Star Atlas; but this latter task was made very rapidly, and without any pretensions to absolute accuracy. "In the United States, where the sky is of extraordinary clearness, the Galaxy sometimes appears all flaky and sparkling with stars, which appear as minute clusters, and at times seem to blaze forth with 'star-dust.' "The critique I will make concerning my drawing is that the dark channels dividing the luminous masses are a little too dark, and that it would more nearly represent the truth if these dark gaps were slightly illuminated, so that the contrast between the bright and the dark portions should become less marked." Elaborate representations of the regions of the Galaxy south of 12°5 of northern declination became accessible in 1877 by the publication of the Atlas of the Uranometria Argentina, one of the results of the great work accomplished by Dr. Gould and his assistants at Cordoba. "The position and ramification of the Milky Way were elaborately delineated by Mr. Thome, and minutely scrutinised by direct comparison with the heavens during the preparation of each map" (Uranometria Argentina, p. 9). The drawings "exhibit many details of outline and contrasts of brilliancy, which are not clearly perceptible except upon the clearest and darkest nights" (p. 344). "The mode of representation which has been adopted was required by the photographic process of transfer, which is inadequate to an equal and exact reproduction of shading or tints in the original, and made it necessary to employ in its preparation only black ink of uniform colour" (p. 345).. These explanations refer to the detailed representations of the portions of the Milky Way given on ten of the maps, from which any desired information has to be gathered. For the comprehensive sketch on the index map merely fulfils its purpose to serve as an index sketch, and fails in resembling the real aspect of the Galaxy, since in the adopted isographic projection the distances between successive parallels of declination decrease in the ratio of 1: cos (if denotes the polar distance), while the corresponding distances in right ascension increase in the ratio of 1: sec, the ratio of areas not being impaired. In the stereographic projection of not less than 100 degrees radius, which Dr. Boeddicker has adopted for his elaborate Map of the Milky Way as seen in our northern latitudes, the great variation of scale is a most serious drawback. The scale increases indeed equally for both co-ordinates, but at the rate of I: sec2 for arcs, and therefore of 1: sec1 for areas, so that at the polar distances I 1.15 1.28 1:48 1.78 2.22 290 4'00 5 86 The necessity of making due allowance for this distortion in all studies of the drawing renders the correct interpretation of its many delicate features, and the proper comparison of the evidence, which is to be found in the details, needlessly troublesome and difficult. Fair justice does not seem to have been done to the high value of the original sectional drawings by their being unsuitably combined. A comprehensive drawing, representing the whole girdle of the Galaxy, on a uniform scale and without appreciable distortion, and allowing direct comparison of all its parts, such as I had in view when I prepared my old paper, is not yet in existence. It is, however, not for the purpose of making another appeal to the comparatively few observers, who might give their help as competent draughtsmen in the production of such a drawing, that I have prepared the greatly enlarged galactic catalogue contained in the present paper. The chief reason why I have not grudged the time which its preparation has cost, is the consideration that the regular watching and controlling of the richest regions of the heavens for the timely discovery of the brighter variable, and especially temporary, stars may thereby be rendered comparatively easy to all observers who are willing to take part in the watching. But for the purpose it is important, and almost essential, that they should prepare their star-maps with their cwn hands. Let them select any special region in the zone of the Galaxy, and lay down the galactic places of the stars within the region on properly prepared paper (be it millimetre paper or paper covered with subdivisions of inches). The mere insertion of the places, and their being marked by suitable discs according to the various magnitudes, will already be of great help in procuring acquaintance with the selected region. The comparisons with the heavens may then be made in the usual way by letting light shine on the map. But in order to save the eyes from much of the usual strain occasioned thereby, let the map be darkened on the back, or mounted on dark paper, and let the star-places be pricked by means of pricking needles of suitable diameters, the needles being mounted on pieces of cork, so that they may he heated to make clean holes, if some better contrivance is not found. The comparisons with the heavens may then be made in the dark, by letting some concealed light be seen through the holes, and they will be found far more expeditious and satisfactory than when made in the usual way. As regards the question of scale, the suggestion of an inch for five degrees, or a centimetre for two degrees, still seems to me, for unaided vision, the most practical, except perhaps if paper is used on which the inch is subdivided into twenty parts in groups of five, when an inch for four degrees will be more convenient. As regards the star discs, proper experiments should be made to decide upon the most suitable size. If the discs are to be proportional to the amount of light, the diameter & of a star of magnitude m should be such that log 8 = 0·2 (m。 — m), if I is the diameter of a star of magnitude mo. But the condition renders the discs of bright stars unnaturally large, so that some compromise will be preferable. The following catalogue supplies the galactic longitudes and latitudes of all the stars down to the magnitude 6mo of the Harvard Photometry (H. P.), or 6m.2 of the Uranometria Argentina (U. A.), which are within twenty degrees of the central line of the Galaxy, for which I have retained the assumptions of my former paper, which differ little from Argelander's, and according to which the pole of the Galaxy is in right ascension 12h 40m, and declination +30° for 1880'0, so that the inclination of the central line to the equator is 60°, and the ascending node, from which the galactic longitudes are reckoned, in right ascension 18h 40m. The central line of the Galaxy, according to Gould's later determination, makes an angle of 2070 with the assumed one, but as I could not afford to repeat my old computations, it will be sufficient if I supply at the end of the catalogue the data for inserting on the map Gould's line, equator, ecliptic, &c. Besides the stars mentioned, the catalogue contains a number of lesser stars, which have been inserted for various reasons, also a considerable number of stars outside the twenty degrees limits. The magnitudes stated are those of the Harvard Photometry and of the Uranometria Argentina, except in the case of variable stars, when the limits of variability, taken from the latest lists, are given. The sign d of duplicity is not added, if the comes is too faint to appreciably affect the magnitude. If a star is placed in different constellations, both constellations are mentioned. The last columns give the right ascension a and declination & for 1880'0. |