Up to about 300 b.c. it can scarcely be said that an observatory existed anywhere, as the crude observations of the heavens then taken were only made by individuals and at intervals, employing the simplest possible apparatuses. But, when philosophical speculation had exhausted its resources, and an accumulation of facts was found to be necessary before the knowledge of the construction of the universe could advance farther, the first observatory was founded at Alexandria, and continued in activity for about four hundred years, or until the middle or end of the 2d century of the Christian era. It was here that Hipparchus, the founder of modern astronomy, by repeating observations made by his predecessors, discovered the precession of the equinoxes, and investigated with considerable success the motions of the sun, moon, and planets. His work was continued by more or less distinguished astronomers, until Ptolemy (in the 2d century a.d.) gave the astronomy of Alexandria its final development. When science again began to be cultivated after the dark ages which followed, we find several observatories founded by Arabian princes; first one at Baghdad (and possibly one at Damascus), built by the caliph Al-Mamùn early in the 9th century, then one on the Mokattam near Cairo, built for Ibn Yιinis by the caliph Hâkim (about 1000 a.d.), where the Hâkimite tables of the sun, moon, and planets were constructed. The Mongol khans followed the example; thus arose the splendid observatory at Merâgha in the north-west of Persia, founded about 1260 a.d. by Hulagu Khan, where Nâsir al-din Tùsi constructed the Ilohkhanic tables; and in the 15th century the observatory at Samarkand was founded by Ulug Begh, and served not only in the construction of new planetary tables but also in the formation of a new catalogue of stars.

With the commencement of scientific studies in Europe in the 15th century the necessity of astronomical observations became at once felt, as they afforded the only hope of improving the theory of the motions of the celestial bodies. Although astronomy was taught in all universities, the taking of observations was for two hundred years left to private individuals. The first observatory in Europe was erected at Nuremberg in 1472 by a wealthy citizen, Bernhard Walther, who for some years enjoyed the co-operation of the celebrated astronomer Regiomontanus. At this observatory, where the work was continued till the founder’s death in 1504, many new methods of observing were invented, so that the revival of practical astronomy may be dated from its foundation. The two celebrated observatories of the 16th century, Tycho Brahe’s on the Danish island of Huen (in activity from 1576 to 1597) and that of Landgrave William IV. at Cassel (1561-97), made a complete revolution in the art of observing. "While the credit of having vastly improved the astronomical instruments perhaps should be φvided equally between Tycho Brahe and the landgrave’s astronomer Biirgi, the former may claim the honour of having been the first to see the necessity of carrying on for a number of years an extensive and carefully-planned series of observations with various instruments, worked by himself and a staff of assistants. In this respect his observatory (Uraniburgum) resembles our modem larger institutions more closely than do many observatories of much more recent date. The mighty impulse which Tycho Brahe gave to practical astronomy at last installed this science at the universities, among which those of Leyden and Copenhagen were the first to found observatories. We still find a large private observatory in the middle of the 17th century, that of Johannes Hevelius at Dantzic, but the foundation of the royal observatories at Paris and Greenwich and of numerous university observatories shows how rapidly the importance of observations had become recognized by governments and public bodies, and it is not until within the last hundred years that the development of various new branches of astronomy has enabled private observers to compete with public institutions.

The instruments employed in observatories have of course changed considerably during the last two hundred years. When the first royal observatories were founded, the principal instruments were the mural quadrant for measuring meridian zenith distances of stars, and the sextant for measuring distances of stars inter se, with a view of determining their difference of right ascension by a simple calculation. These instruments were introduced by Tycho Brahe, but were subsequently much improved by the addition of telescopes and micrometers. When the law of gravitation was discovered it became necessary to test the correctness of the theoretical conclusions drawn from it as to the motions within the solar system, and this necessarily added to the importance of observations. By degrees, as theory progressed, it made greater demands for the accuracy of observations, and accordingly the instruments had to be improved. The transit instrument superseded the sextant and offered the advantage of furnishing the difference of right ascension directly; the clocks and chronometers were greatly improved; and lastly astronomers began early in the 19th century to treat their instruments, not as faultless apparatuses but as imperfect ones, whose errors of construction had to be detected, studied, and taken into account before the results of observations could be used to test the theory. This century has also witnessed the combination of the transit instrument and the mural quadrant or circle in one instrument,—the transit or meridian circle.

While the necessity of following the sun, moon, and planets as regularly as possible increased the daily work of observatories, other branches of astronomy were opened and demanded other observations. Hitherto observations of the “fixed stars” had been supposed to be of little importance beyond fixing points of comparison for observations of the movable bodies. But when many of the fixed stars were found to be endowed with “proper motion,” it became necessary to include them among the objects of constant attention, and in their turn the hitherto totally neglected telescopic stars had to be observed with precision, when they were required as comparison stars for comets or minor planets. Thus the field of work for meridian instruments became very considerably enlarged.

In addition to this, the increase of optical power of telescopes revealed hitherto unknown objects—double stars and nebulae—and brought the study of the physical constitution of the heavenly bodies within the range of observatory work. Researches connected with these matters were, however, for a number of years chiefly left to amateur observers, and it is only within the last fifty years that many public observatories have taken up this kind of work. The application of spectrum analysis, photography, photometry, &c., in astronomy has still more increased the number and variety of observations to be made, so that it has now become necessary for most observatories to devote themselves to one or two special fields of work.

It would be difficult to arrange the existing observatories into classes either according to the work pursued in them or their organization, as the work in many cases at different times has been directed to different objects, while the organization depends mostly on national and local circumstances. As already alluded to above, one of the principal characteristics of the larger observatories of the present day is the distribution of the work among a number of assistants under the general superintendence of a director. This applies principally to the great observatories, where the sun, moon, planets, and a limited number of fixed stars are without interruption being observed, but even among these institutions hardly two are conducted on the same principles. Thus in Greenwich the instruments and observations are all treated according to strict rules laid down by the astronomer-royal, while in Washington or Pulkowa each astronomer has to a certain extent his choice as to the treatment of the instrument and arrangement of the observations. The same is the case with the smaller institutions, in most of which these arrangements vary very much with change of personnel.

The way in which the results of observations are published depends principally on the size of the institutions. The larger observatories issue their “Annals” or “Observations” as separate periodically-published volumes, while the smaller ones chiefly depend on scientific journals to lay their results before the public, naturally less fully as to details. Among these journals the principal are :— Berliner Astronomisches Jahrbuch (for the years 1776 to 1829), Monatliche Correspondenz (edited by Von Zach, 28 vols., 1800-13), Astronomische Nachrichten (founded 1821; 107 vols, in 4to, still appearing with two vols, per annum), Memoirs of the Royal Astronomical Society (47 vols. 4to, from 1822), and Monthly Notices of the Royal Astronomical Society (44 vols. 8vo, from 1827).

Subjoined is a catalogue of public and private observatories now in activity or which have existed within the last hundred years.

Great Britain and Ireland.

A. Public Observatories.

Greenwich, royal observatory, lat. + 51° 28' 38" , 4. Founded in 1675 for the promotion of astronomy and navigation. The observations have therefore from the first been principally intended to determine the positions of standard stars, the sun and planets, and above all to follow the motion of the moon with as little interruption as possible, both on and outside the meridian. Since 1873 spectroscopic observations and a daily photographic record of sun-spots have been taken. The observatory is under the direction of the astronomer-royal; and from the time of its first astronomer, Flamsteed, the institution has always maintained its place in the foremost rank of observatories. Thus the observations of Bradley (ob. 1762) form the foundation of modern stellar astronomy; but it was especially during the directorship of Airy (1835-81) that the observatory rose to its present high state of efficiency. There are now a chief assistant, eight assistants, and a staff of computers employed. The principal instruments now in use are :—a meridian circle by Simms (and Ransomes and May as engineers), erected in 1850, having a circle of 6-feet diameter and a telescope of 8-inches aperture; a large chronograph (1854); an altazimuth by Simms and Ransomes and May, for observations of the moon, erected in 1847, with 3- feet circles and 4-inch telescope; an equatorial refractor by the same makers (O.G. 12 ’ 8 inches, by Merz), mounted in the “English” manner with long polar axis, chiefly used for spectroscopic work; photoheliograph by Dallmeyer of 4-inches aperture, smaller equatorials, clocks, &c. The standard “motor clock” is the centre of a system of electrically r controlled clocks scattered over many provincial towns in the three kingdoms. The magnetical and meteorological department was founded in 1838; it contains a complete set of instruments giving continuous photographic records of magnetic declination, horizontal and vertical force, barometric pressure, dry and wet bulb thermometers, &c. The Observations are published with all details from 1750, beginning with 1836 in annual bulky 4to volumes; special results— e.g., five Star Catalogues, Reductions of Lunar and Planetary Observations— are published in separate volumes.

Oxford, Radcliffe Observatory, lat. + 51°45'36"∙0,long. 0 h 5 m 2 s, 6W. Founded in 1771 by the Radcliffe trustees at the instance of Professor Hornsby. Observations were regularly made, but none were published until Manuel J. Johnson was appointed Radcliffe observer in 1839, when systematic observations λvere commenced with an 8-feet transit instrument by Bird (1773) and a 6-feet mural circle by Jones (1836). Johnson was succeeded in 1860 by Rev. R. Main, who died in 1878, and was followed in 1879 by E. J. Stone. Heliometer (7∣ inch) by Repsold (1849); meridian circle by Troughton and Simms, mounted in 1861, formerly belonging to Mr Carrington; self-recording meteorological instruments. The staff now consists of three assistants. Besides the annual 8vo volumes of Observations. (from 1840), two catalogues of respectively 6317 and 2386 stars, chiefly circumpolar (1860 and 1870) have been published.

Oxford, university observatory, lat. + 51° 45' 34' z ∙2, long. 0 h 5 m 0 s- 4W. Finished in 1875; is under the Savilian professor of astronomy; there are two assistants. 12∣-inch equatorial refractor by Grubb, and a 13-inch reflector made and presented by Mr De La Rue. The former is used for micrometer work (chiefly on clusters of stars) and photometric observations; the latter for taking lunar photographs, by means of which the director, Professor Pritchard, has investigated the libration of the moon. No. 1 of Astronomical Observations (8vo) was published in 1878.

Cambridge, lat. + 52° 12' 51"‘6, long. 0 h 0 m 22 s '8 E. Founded by the university senate in 1820. Directors: G. B. Airy, 1828 to 1835; J. Challis, to 1861; J. C. Adams. Chiefly devoted to meridian work,—up to 1870 with a 5-inch transit by Dollond and a mural circle by Jones; a new meridian circle by Simms, of 8-inches aperture and 3-feet circles, was then erected, and is being used for determining the places of all the stars down to 9 - 0 mag. between + 25° and + 30° decl. The “Northumberland equatorial” was mounted in the “English” fashion in 1838; the object-glass by Cauchoix is of ll⅛-inches aperture and 19-feet focal length. The Observations from 1828 to 1865 are published in 21 4to volumes.

Durham, lat. + 54° 46' 6"‘2, long. 0 h 6 m 19 s- 8 W. Founded in 1841, principally by private subscription; is under the direction of the professor of mathematics and astronomy in the university. There is a small meridian circle by Simms, and an equatorial refractor by Fraunhofer of 6⅜-inches aperture, with which minor planets, comets, and double stars have been observed. The results from the years 1846-52 have been published in 2 8vo volumes.

Liverpool (Bidston near Birkenhead), lat. + 53° 24' 4", long. 0 h 12 m 17 s- 2 W. Founded in 1838 by the municipal council; transferred in 1856 to the Docks and Harbour Board; moved to Birkenhead in 1867. Specially intended for testing the rates of chronometers under different temperatures. Transit instrument by Troughton and Simms, and an 8-inch equatorial by Merz.

Kew (Richmond), lat. + 51° 28' 6", long. 0 h l m 15 8- 1 W. The central meteorological observatory of the United Kingdom, with self-registering meteorological and magnetical instruments. Established in 1842 under the auspices of the British Association, afterwards transferred to the Royal Society. A photoheliograph was employed at Mr De La Rue’s expense to take daily sun-pictures from 1863 to 1872.

Edinburgh, royal observatory, lat. + 55° 57' 23" , 2, long. 0 h 12 m 43 s, 0 W. Founded in 1811 by subscription; the building on the Calton Hill erected in 1818. In 1834 the founders handed over the administration to the Government, and in 1846 the ownership was similarly transferred. Since 1834 the observatory has been under the direction of the astronomer-royal for Scotland, who is also professor of practical astronomy in the university; there are two assistants. Professor T. Henderson (1833 to 1845) commenced extensive meridian observations of fixed stars, since continued by his successor, C. Piazzi Smyth. The mural circle of 6-feet diameter and 8-feet transit are now out of date. A reflector of 2-feet aperture by Grubb (silver on glass) was erected in 1872, but has never been quite finished nor come into use. Observations with deep-soil thermometers have been carried on since 1837, and delicate spectroscopic investigations made by the present astronomer, partly abroad. Observations and results have been published in 14 4to volumes.

Glasgow, lat. + 55° 52' 42" ’ 8, long. 0 h 17 m 10 s- 6 W. Organized in 1840 by subscription, aided by subsidies from the university and the state; is under the professor of astronomy. Meridian circle by Ertel with 42-inch circles, and telescope of 6-inches aperture; equatorial of 9-inches aperture. A catalogue of 6415 stars from meridian observations made since 1860 was published in 1883 by the present director, R. Grant. The observatory was (1868-83) one of the seven first-class meteorological stations.

Dublin, situated about 4 miles north-west of Dublin at Dunsink, lat. + 53° 23' 13"'0, long. 0 h 25 m 21 s W. Belongs to the university; erected in 1785; is under the direction of the “Andrews professor of astronomy and royal astronomer of Ireland.” There is one assistant. In 1808 a reversible meridian circle by Ramsden and Berge of 8-feet diameter was put up, with which Brinkley observed assiduously till 1827, though of his results those relating to stellar parallax were affected by certain instrumental errors which rendered them of no value. Sir W. R. Hamilton (1827-65) devoted himself exclusively to mathematics. In 1868 was erected an equatorial refractor, object-glass of ll∣-inches aperture by Cauchoix (formerly belonging to and given by Sir J. South), which has been used by Briinnow and his successor R. S. Ball (since 1874) for researches on stellar parallax. A meridian circle by Pistor and Martins of 6 - 4-inches aperture was mounted in 1873 and a large chronograph in 1882; they are used for observing stars possessing special interest (red stars, stars with proper motion, &c.). Astronomical Observations and Researches made at Dunsink, parts 1-5, 4to, 1870-84.

Armagh, lat. + 54° 21' 12" ’ 7, long. 0 h 26 m 35≡ ’ 5 W. Founded and endowed by Archbishop Robinson in 1791. Possessed very few instruments until the observatory was enlarged by Archbishop Lord John Beresford in 1827, when a mural circle and a transit by Jones were provided, with which T. R. Robinson (director from 1823 to 1882) observed the stars contained in the catalogue of 5345 stars published in 1859. With the mural circle, to which had been added a 7-inch telescope by T. Grubb (in 1862), about 3000 stars have been observed since 1864, and these are now (1884) ready for press. There is also a 15-inch reflector. Armagh was (1868-83) one of the seven first-class meteorological observatories.

Cork, observatory of Queen’s College, lat. + 51° 53' 30", long. 0 h 33 m 58 s W. Erected in 1878 at the expense of Mr Crawford of Cork; 8-inch refractor, 4-inch siderostat and transit circle, by Grubb. Managed by the professor of natural philosophy.

B. Private Observatories now existing.

Mr J. G. Barclay's observatory, Leyton, Essex, lat. + 51° 34' 34", long. 0 h 0 m 0 s- 9 W. In activity since 1862; 10-inch refractor by Cooke; chiefly devoted to double stars; small transit circle. Four parts of Observations have been published (4to, 1863-77).

Mr A. A. Common’s observatory, Ealing, London, W. Silvered-glass reflector of 36-inches aperture (mirror by Calver, mounting by the owner), erected in 1879; chiefly used for celestial photography. Also 18-inch silvered-glass reflector erected in 1876.

Colonel Cooper’s observatory, Markree Castle, Sligo, Ireland, lat. 54° 10' 31" ’ 8, long. 0 h 33 m 48 8 '4 W. Founded by the late E. J. Cooper, who in 1834 erected an equatorial refractor of 13 ’ 3-inches aperture (glass by Cauchoix). In addition to numerous other observations this instrument was from 1848 to 1856 used for determining the approximate places of 60,000 stars near the ecliptic {Markree Catalogue, 4 vols. 8vo, 1852-56). The observatory was restored in 1874, and the refractor has since been used for double-star observations. There is also a transit circle by Ertel.

Earl of Crawfords observatory, Dun Echt, Aberdeenshire, lat. + 57° 9' 36", long. 0 h 9 m 40 8 W. Founded in 1872; is one of the best - equipped observatories existing; has 15-inch equatorial refractor by Grubb, large chronograph (driven by same clock as the refractor), 12-inch silvered reflector by Browning, two 6-inch and several smaller refractors, meridian circle by Simms similar to the one at Cambridge, numerous spectroscopes and minor instruments, also a large library, and a collection of physical instruments. Cometary and spectroscopic observations and reduction of the observations made by the Venus expedition to Mauritius in 1874 have hitherto principally occupied the staff. Three 4to volumes of Publications and very frequent Dun Echt Circulars, distributing news of discoveries (chiefly relating to comets), have been issued.

Mr E. Crossley's observatory, Bermerside, Halifax, Yorkshire. Equatorial refractor by Cooke of 9 - 3-inches aperture, erected in 1871, chiefly used for observations of double stars.

Dr W. Huggins's observatory, Upper Tulse Hill, London, lat. + 51° 26' 47", long. 0 h 0 m 27 8 *7 W. Founded in 1856; furnished with an 8-inch refractor (glass by Clark, mounting by Cooke). In 1870 was erected...