8 August 1837

Instructions of Astronomical Nature and list of cases containing the various parts of Bradley’s Zenith Sector from Sir George Airy, Astronomer Royal.
4pp. These notes accompanying the instruments were sent to Thomas Maclear at the Cape.

Bradley’s 12½-foot Zenith Sector is famous as the telescope with which he discovered the two phenomena ‘aberration of light’ and ‘nutation’. Made by George Graham, it was commissioned by James Bradley in 1727 for use in his uncle’s private observatory in Wansted (Wanstead) in North-East London. Bradley was appointed Astronomer Royal in 1742. When in 1749, he was granted £1000 to re-equip the Observatory at Greenwich, he used £45 of the money to formally acquire the Zenith Sector for use there. At Greenwich Bradley and his successors used it to check the line of collimation of the meridian telescopes. Between 1749 and 1837, a number of significant alterations were made to improve its operation. In May 1837, it was sent to the Cape Observatory for the verification and extension of La Caille’s arc of meridian at the Cape of Good Hope, returning to Greenwich in 1850 where it was hung as a relic on the west wall of the Transit Room in the Meridian Building. The telescope was taken down in 1952/3 for cleaning and conservation by the British Museum and the National Maritime Museum. It was one of the telescopes on public display in the Octagon Room in Flamsteed House when it first opened to the public on 8 May 1954. The instrument was formally acquired by the National Maritime Museum in 1955/6 (Object ID: AST0992). Following the refurbishment of the Meridian Building in 1967, it was moved to its 1779 position on the west side of the Quadrant Room where it remains to this day. It is one of the most historically important instruments on display.

From the estate of Sir Thomas Maclear (17 March 1794 – 14 July 1879) an Irish-born Cape Colony astronomer who became Her Majesty's astronomer at the Cape of Good Hope. He worked with John Herschel until 1838, performing a survey of the Southern Sky, and continued to perform important astronomical observations over several more decades.

Sir George Biddell Airy KCB FRS (27 July 1801 – 2 January 1892) was an English mathematician and astronomer, as well as the Lucasian Professor of Mathematics from 1826 to 1828 and the seventh Astronomer Royal from 1835 to 1881. His many achievements include work on planetary orbits, measuring the mean density of the Earth, a method of solution of two-dimensional problems in solid mechanics and, in his role as Astronomer Royal, establishing Greenwich as the location of the prime meridian.

R7,500