Halley was succeeded in the office of Astronomer Royal by Bradley, who had already rendered his name for ever illustrious by his dis covery of the aberration of light. In 1749, the Observatory having been furnished with a brass quadrant of eight feet radius, constructed by the celebrated artist, Bird, Bradley commenced a aeries of observa tions with the new instrument, which he continued to prosecute till shortly before his death in the year 1762. The results of his labours were subsequently published at the expense of the University of Oxford in two folio volumes, the first volume in 1798, under the superintendence of Dr. Hornsby, and the second in 1805, under the editorship of Dr. Robertson.
Bradley's observations of the stars have been reduced and discussed by the celebrated Besse! in a work published at Konigsberg, in one volume folio, in the year 1818, entitled,' Fundamenta Astronomise pro arum 1755, deducta ex observationibus viri incomparabilis James Bradley, in specula Astronomica Grenovieensi per annos 1750-62 institutis.' Bradley is universally regarded as one of the greatest observers of ancient or modern times. The year 1750, when he commenced his labours with Bird's quadrant, may be considered as the epoch whence date observations comparable in precision with those of the present day. Henceforward the observations made at Greenwich have been employed almost exclusively in all the more important investiga tions of astronomy. Nor must we omit to state, that it was during his career as Astronomer Royal that Bradley made the series of observations, which resulted in his great discovery of the nutation of the earth's axis.
The successor of Bradley was Dr. Bliss, Savilian Professor of Geometry in the University of Oxford, who died in 1765. The next Astronomer Royal was the famous Dr. Maskelyne. His observations embraced the determination of the positions of the sun, moon, and planets, and a select number of stars; and he continued to adhere to this plan throughout the whole period of his career. Maskelyno first introduced the practice of observing the transit of a star at five vertical wires of the telescope. He was also the first who noted the transit of a star in terms of tenths of a aecond. His death occurred in the year 1811. The results of his observations have been published in four folio volumes.
Maskelyne was succeeded by Pond, who had already distinguished himself as a practical astronomer, having in the year 1806 communi cated a paper to the Royal Society, in which he demonstrated that the brass quadrant of the Royal Observatory had undergone a change of form since its erection in Bradley's time. It was doubtless this circumstance which induced Maskelyno to solicit from the Government the construction of a mural circle of six feet diameter by Troughton, a request which was complied with ; but the instrument was not quite finished at the time of his death. Soon after his accession to the office
of Astronomer Royal, Pond commenced a series of observations with the mural circle, in the prosecution of which he evinced a high degree of talent. He first introduced the practice of observing a star by direct and reflected vision. The objects of his labours, besides the sun, moon, and planets, included also a considerable number of the stars. The observations in right ascension at the Royal Observatory, subsequently to the year 1816, were made with a new transit instrument of ten feet focal length, constructed by Troughten. In 1833, Pond published a catalogue of 1112 stars, which proved of great value to the practical astronomer. He retired from office in 1835, and died in the following year.
Pond was succeeded by Mr. Airy, who still continues to hold the office of Astronomer Royal. He had been previously Plumian Professor of Astronomy in the University of Cambridge, and had also been Director of the Cambridge Observatory since the year 1S28. While engaged in the latter capacity he set the example of reducing all his observations as soon as they were made, a practice which has since been adopted at all public observatories. This eminent astronomer has signalised the period of his career at the Royal Observatory by numerous operations of great importance. Upon his recommendation, the Lords Commissioners of the Admiralty defrayed the expenses of reducing all the observations of the moon and planets made at Green wich from 1750 to 1830. The results for the planets were published in 1846, in one quarto volume ; those relating to the moon were given to the public in 1848, in two large quarto volumes. Several important catalogues of stars have emanated from the Royal Observatory during Mr. Airy's directorship. [ASTRONOMY.] In the instruments of the Observatory great improvements have also been effected. In 1847 an altitude and azimuth circle of a peculiar construction (termesi an altazhnuth) was erected, for the special purpose of making observa tions of the moon out of the meridian. In 1851 a powerful transit circle was erected, and henceforward all observations, both of right ascension and polar distance, were made with the same instrument. In 1852, an instrument termed the reflex zenith tube was erected, the object of which is to make observations near the zenith, mainly for the purpose of determining the value of aberration. In 1853 the American method of recording transits of stars by eleetro-magnetism was introduced at Greenwich. In 1859, observations were commenced with a magnificent cquatorially mounted refractor of 12 inches aperture. It may be remarked, finally, in connection with this brief sketch of the Royal Observatory, that a great number of chronometers for the Admiralty are being constantly rated at the same establishment.