Modern Observatories.—The names and locations of nearly 30o active observatories will be found in the Nautical Almanac for 1930. The progress of astronomy and the changes in the aim of celestial research have brought changes in the characteristics of observatories. At the beginning of the 19th century the equip ment of a public observatory may be said to have consisted of a meridian instrument with an equatorial as subsidiary; today the latter is generally the more important instrument, and often is supplemented by plate measuring apparatus.
The routine determination of the positions of sun, moon, the planets and stars still continues as staple work at Greenwich, Washington and other national observatories, for such records are necessary for the maintenance of fundamental astronomy. But the Government and university observatories have now added equatorial instruments, generally large, and frequently adapted for photography, to their equipment and pursue in addition some branch of astrophysical work.
Outstanding facts of the loth century have been the making of large telescopes, in some cases of novel design for special re searches, and the establishment of branches to existing observa tories in places considered more suitable meteorologically than those of their parents. The earliest example is the solar observa tory set up on Mt. Wilson, 5,7ooft. above sea-level, near Pasa dena, California, in 1904–o5 as an offshoot of the Yerkes observa tory. This observatory is now at the charge of the Carnegie Institution of Washington. In 1918 the word "solar" was dropped since the physical qualities of stars other than the sun are there studied. The instruments are on the mountain for observing. The library, laboratory and administrative offices of the observatory are in the valley below. A new type of telescope has been evolved for solar observation—the tower telescope. A revolving mirror known as a coelostat, and a fixed mirror on the top of a tower reflect the sun's light through an object-glass downwards, to form an image of the sun on the slit of a spectroscope in a pit below. The light then passes through the spectroscope to record itself on the photographic plate, or to be otherwise examined, the scheme obviating the difficulty of carrying long instruments on a moving frame. This observatory has a tower telescope 15oft. high
and also a reflecting telescope with a mirror iooin. in diameter, the largest yet in use (See Plate under TELESCOPE), carried in the usual manner on an equatorial mounting, and with this is an Inter ferometer for measuring the size of the stars. Another large tele scope is the 72in. reflector at the Dominion of Canada Astrophysi cal observatory established in 1916 at Victoria, B.C., as a branch of the Dominion observatory at Ottawa, that itself had grown from a modest establishment used by the Survey department. In the eastern hemisphere an observatory specially adapted for solar investigation was established at Canberra by the Federal Govern ment of Australia as a link in the chain of such institutions round the world, of which the Solar Physics observatory at Cambridge (England) (removed from South Kensington in 1911) and that at Kodaikanal, southern India (which was established as a Gov ernment institution about 190o and replaces, in part, the observa tory of the Government of Madras founded in 1792), are others. A site has been chosen in south-west Africa under the auspices of the Smithsonian institution of Washington for a station for the special study of solar radiation. The Harvard southern station has been transferred from Arequipa in Peru to Mazelspoort, 14m. from Bloemfontein, Yale university observatory has set up a southern branch at Johannesburg; and the Ann Arbor observa tory of Michigan has lately done the same at Bloemfontein by the help of a generous donor, the principal instrument being a refractor of 27in. aperture, that is to be used largely for ob serving double stars. In the same connection it may be noted that the observatory of the Union of South Africa at Johannes burg which dates under its present name from 1912 (having pre viously been known as the Transvaal observatory, when it was mainly a meteorological station) has lately procured a 26in. re fracting telescope, so that, including the Royal observatory at Capetown, there are now five observatories with large instruments in this part of the globe as well as several belonging to amateurs who work on special lines. On the other hand the observatory at Durban, in charge of the colonial Government of Natal, was closed in 1912.