Abstract
LONDON
Royal Astronomical Society, December 10. - Second Meeting of Session. Admiral Manners, president, in the chair during the early part of the meeting; afterwards (the president finding his health not sufficiently restored to enable him to remain), Mr. De la Rue, F.R.S., vice-president, took the chair. The minutes of the last meeting were read and confirmed, and thirty-two presents announced, including a magnificent representation of the solar spectrum from France (showing the part beyond the violet end), presented by Mr. Ladd. Mr. Williams, the assistant secretary, then read a series of extracts from an elaborate work on Chinese Astronomy, upon which he has been engaged during the last three years. He exhibited in a very complete and lucid manner the Chinese mode of reckoning time by cycles of sixty years, the several years of each cycle being indicated by certain characters called Kea Tsze. He then showed how any year in ordinary chronology, whether B.C. or A.D., can be represented in the proper cycle, and in its right place in that cycle. He described the division of the heavens into thirty-one parts; three, called “Yuen,” of large size; the remainder, called “Suh,” representing lunar houses, and very irregular in extent, both from east to west and from north to south. While one, for instance, extended north and south from Perseus to Canopus, another consisted mainly of a few stars in the head of Orion. Other extracts exhibited the correctness of the positions assigned by the Chinese to the equinoxes and the solstices, and the evidence their estimates give respecting the date at which, their observations were made. He mentioned inter alia that the Metonic Cycle had been known to the Chinese astronomers 2,000 years before Meton's day. The occurrence of the names of our modern asterisms in Chinese records must not be held to indicate the antiquity of our constellation-figures, because it cannot be doubted that the Jesuits taught the Chinese these new names. In fact, the Chinese were led to remodel their system of astronomy according to the instructions of the Jesuits—a misfortune, perhaps, since, although the old system of astronomy had had the disadvantage of being inexact and scarcely intelligible, the change destroyed many of the clues by which we might have found clearer ideas as to what the Chinese astronomers really meant to record.—The Astronomer Royal indicated his high opinion of the value of such researches as those in which Mr. Williams had been engaged. Astronomy is the science which of all others brings most together the past, the present, and the future, and, therefore, all studies of long past eras, even though the astronomical observations then made were comparatively inexact, cannot but have a high value. Mr. Stone, F.R.S., called attention to the general value of the matter brought before the society's notice by Mr. Williams, but expressed his regret that the Chinese records named only the day on which any phenomenon was observed. Mr. De la Rue then mentioned that the greater part, if not all, of Mr. Williams's work, would be printed in the Society's Memoirs.—The Astronomer Royal described an arrangement for correcting atmospheric chromatic dispersion, even simpler than those he had before devised. It had occurred simultaneously to himself and to Mr. Simms, the optician, and consists simply in giving the eye-glass of an eyepiece such a motion that while the face towards the field-glass presents an unchanged curvature, the other face (plane) is slightly inclined. This is clearly equivalent to the addition of a prism to the eye-glass, only there is no loss of light, as there would be were a separate prism added. The new eye-piece will serve also to correct errors in the centreing of an object-glass.—Professor Cayley discussed certain geometrical relations connected with the problem of determining the p]ace of a body revolving round the sun, from three observations. He remarked that each observation shows, that the body lies on a known line. If we tnke these three lines in space, what the problem really requires is, that we should determine the position of a plane passing through the sun, and intersecting these lines so that a conic through the points of intersection should hnve the sun in its focus, and the areas between vectoral radii to the points proportional to the two observed time-intervals. He then considered the locus of the orbit-pole, (I) for an assumed eccentricity, (2) for an assumed period, on a stereographic projection of a portion of the sphere—equal in extent to one half, but not actually a hemisphere. The loci for poles to real orbits—that is, orbits having all three points on one branch—exhibit a singular figure, the true locus having points d'arrêt on the bounding-lines of the half-sphere of projection. In answer to questions by the Astronomer Royal, Mr. De la Rue, and Mr. Stone, Professor Cayley indicated that his paper was intended rather as a contribution to the geometry of the problem than to its practical solution.—Dr. Balfour Stewart then read a paper on terrestrial magnetism. After referring to the views he has already published respecting the earth's magnetic character, he indicated his belief that the zodiacal light is a phenomenon of terrestrial magnetism, owing its existence to the magnetic effects produced by the upper air-currents (the counter-trades); these effects not being recognisable, of course, in ordinary observations. He suggested also that the motion of the tidal wave might account for the magnetic variations, whose period corresponds to the lunar diurnal motion. The Astronomer Royal remarked on the complexity of the whole problem of terrestrial magnetism, which hs characterised as hardly belonging to the class of subjects usually dealt with by the Society.—Mr. Proctor gave a brief sketch of a new theory of the Milky Way. He regards the galaxy as neither a cloven disc, as Sir W. Herschel opined, for a flat ring as Sir J. Herschel has suggested, but a spiral of a figure which he indicated as serving to explain all the most striking peculiarities of the Milky Way, as seen upon the heavens.—Another paper by Mr. Proctor, on Great Circle Sailing, and a letter from Lieut. Tupman about the November meteors as seen in Egypt, remained unread owing to the lateness of the hour.
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Societies and Academies . Nature 1, 221–226 (1869). https://doi.org/10.1038/001221c0
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DOI: https://doi.org/10.1038/001221c0