Airy, Sir George Biddell

Sir George Biddell Airy, (born July 27, 1801, Alnwick, Northumberland, Eng.—died Jan. 2, 1892, Greenwich, London), English scientist who was astronomer royal from 1835 to 1881.

Airy graduated from Trinity College, Cambridge, in 1823. He became Lucasian professor of mathematics at Cambridge in 1826 and Plumian professor of astronomy and director of the Cambridge observatory in 1828. In 1835 he was appointed the seventh astronomer royal, i.e., director of the Royal Greenwich Observatory, a post he would hold for more than 45 years.

Airy completely reorganized the Greenwich observatory, installing new apparatus and rescuing thousands of lunar observations from oblivion. Most importantly, he modernized the observatory’s system for making extremely precise observations of stellar positions. He wielded great power within the British scientific community, and he opposed government support of pure science, arguing that original research was best left to private individuals and institutions.

Airy was severely criticized for his part in the failure of British astronomers to search for a new planet (Neptune) whose existence and probable location were predicted in 1845 by British astronomer John Couch Adams on the basis of irregularities in the motion of Uranus. A similar calculation was made in the next year by the French astronomer Urbain-Jean-Joseph Le Verrier, which led almost immediately to the discovery of Neptune by German astronomer Johann Gottfried Galle and his student Heinrich Louis d’Arrest at the Berlin observatory. Modern scholars differ on how much blame to give Airy, and from today’s perspective the one-year delay in the discovery of Neptune does not seem very important. However, at the time, it produced a stormy episode in British-French scientific relations.

Airy in 1827 made the first successful attempt to correct astigmatism in the human eye (his own) by use of a cylindrical eyeglass lens. He also contributed to the study of interference fringes, and the Airy disk, the central spot of light in the diffraction pattern of a point light source, is named for him. In 1854 he used a new method to determine the mean density of Earth. This involved swinging the same pendulum at the top and bottom of a deep mine to measure the change in the strength of gravity between the top and bottom of the mine. Airy was also the first to propose (c. 1855) the theory that mountain ranges must have root structures of lower density, proportional to their height, in order to maintain isostatic equilibrium. He was knighted in 1872.