THE DUNSINK OBSERVATORY, DUBLIN.—The third part of “Astronomical Observations and Researches made at Dunsink, the Observatory of Trinity College, Dublin,” has been published by Dr. Ball. It contains four papers, the first by the previous director, Dr. Brunnow, presenting a discussion of observations of the planetary nebula H. IV. 37, the position of which is in R.A. 17h. 58m. 365., N.P.D. 23° 21′.8 for 1880. The nebula appears in the South-refractor as a somewhat elliptical disk, whose major axis is about half a minute, and has in the centre a well-defined point resembling a star of the eleventh magnitude. This point was compared in declination with a star to the north of the tenth magnitude, preceding the nebula by 255., the same method of observing being used that had been adopted in Dr. Brunnow's earlier researches on stellar parallax. The observations extend over thirty-three nights, from 1871, August 13, to 1872, August 6, and their discussion gives for the parallax of the nebula, + 0″.047 ± 0″.030. Prof. Bredichin, in “Annales de l'Observatoire de Moscou,” vol. iii., has found a negative parallax (- 0″.064 ± 0″.039), using also the method of differences of declination with the same star of comparison. The results of these investigations may be taken to indicate that the parallax of this planetary nebula if measurable at all must be very small. The second paper contains Dr. Ball's observations of 61 Cygni, and his determination of its parallax therefrom. By what was at first an inadvertence, instead of using the following of the two components as Dr. Brunnow had done, the preceding one was observed, and the mistake not being remarked until the series was considerably advanced, it was resolved to complete it as begun; perhaps the result possesses for this reason additional interest. Dr. Ball finds for the parallax + 0″.4654 ± 0″.0497, which is about a mean of the values obtained by Bessel, Johnson, Peters, Struve, and Auwers, which appear entitled to the greatest weight. The observations extending from 1877, July 3, to 1878, June 1, are given in their original form. The third paper, also by Dr. Ball, relates to “observations in search of stars with a large annual parallax,” forty-two stars being examined for this purpose, including several red and variable stars: the results, however, are found to be entirely negative as regards the object in view, no amount of parallax worth following up being suggested. The principle upon which the observations were made is fully described and their details appended to the memoir. The last portion of the Dunsink publication contains Dr. Brunnow's measures of double-stars 1870–73.
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Mar 1, 1920
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