S. W. Burnham, of Chicago, is famed for his acuteness of vision, tested in having detected and measured over one thousand double stars which to other eyes had appeared only as single stars. The discovery of these objects belongs wholly to the nineteenth century; for in 1803, Sir William Herschel first announced the existence of sidereal systems composed of two stars, one revolving around the other, or both moving about a common centre. Some of these binary systems have periods of as great a length as fifteen hundred years; and some are as brief as four, and even two days. Some of them afford curious instances of contrasted colors, the larger star red or orange, and the smaller star blue or green. X. THE NATIONAL OBSERVATORY AT WASHINGTON. [Illustration: PROFESSOR WILLIAM HARKNESS, Astronomical Director U. S. Naval Observatory, Washington, D. C.] Professor William Harkness, U. S. N., M. D., LL. D., is widely known as the author of numerous astronomical and physical papers and books. He has also designed a number of instruments and made important discoveries. He has long been connected with the United States Naval Observatory, and now holds the position of Astronomical Director. His report for the year 1898 shows that the twenty-six inch reflector at Washington is now nightly engaged in mapping the relative positions of Rhea and Iapetus, the fifth and eighth satellites of Saturn, with the intention of securing a new and final determination of the mass of that planet, which has been heretofore reckoned as one 3492d of the sun. The twelve-inch telescope is chiefly employed in studying comets and asteroids, and on Thursday evenings is at the service of the public. In the year 1898, 3778 observations were made with the nine-inch transit circle, for which two men were detailed, with the services of five computers. A transit circle and an altazimuth instrument, each turned out of solid steel, have recently been added to the equipment, and are of a workmanship that compares favorably with anything ever manufactured in Europe. It is asserted that the latter instrument will give more accurate measurements of declination than a transit circle, which is an innovation on long-cherished ideas. Professor Simon Newcomb, of the United States Navy, is about to issue new tables of Mars, Uranus, and Neptune, and a “Catalogue of Fundamental Stars for the Epoch 1900.” During the year 1898 three thousand copies of the American Nautical Almanac were published. This is but an illustration of the scientific labor accomplished at this busy hive of industry. During the year this observatory issued to the navy 230 chronometers, 200 sextants and octants, and 1400 other nautical instruments of value. XI. STAR MAPS AND CATALOGUES.