Herschel, A. S. (Alexander Stewart), 1836-1907

Sir George Biddell Airy (1801–1892) was a British astronomer. Airy became Lucasian Professor of mathematics at Cambridge in 1826 and Plumian Professor of astronomy and director of the new Cambridge Observatory in 1828. From 1835 to 1881, he served as Astronomer Royal, a senior post in the Royal Household of the Sovereign of the United Kingdom.

Airy was born in Northumberland, England, to William Airy and Ann Biddell. His father was a tax collector, but he lost his position by the time young Airy was thirteen. As a result, the boy came under the care of his uncle Arthur Biddell, who supported George’s growing interest in science. In 1819, Airy enrolled at Trinity College, Cambridge. Even though he attended on a reduced fee, he had to support himself with taking on pupils. Airy distinguished himself as a disciplined and talented student. Among other honors, he graduated as the top First Class student in 1823. He was also awarded a fellowship at Trinity College where he commenced his academic career.

Airy made many contributions in mathematics, physics and astronomy. One of his first research interests was the achromatism of eyepieces and microspopes. After discovering astigmatism in one of his own eyes, he suggested a successful method for correcting it by using a concave lens with one or two cylindrical surfaces. He also discovered the Airy stress function method, which helps determined strain and stress fields within a beam, and the Airy Wave theory, which describes gravity waves on the surface of a fluid. In addition, he also investigated the mass of Jupiter. One of his most significant accomplisments as an astronomer was the discovery of a new inequality in the motions of Venus and the Earth. For this he received the Gold Medal of the Royal Astronomical Society in 1832.

In 1836, Airy became the Astronomer Royal. He immediately concentrated his efforts on improving the equipment and to reform the procedures and methods by which the Greenwich Observatory had been run until then. The first of the new instruments, an altazimuth designed primarily to observe the moon, was installed in 1847. Among the other equipment, most of which was designed by Airy himself, were a new meridian circle, a new equatorial, a double-image micrometer. Under his direction, observations were made with uninterrupted regularity. The editor of his autobiography noted that the “ruling feature of his character was undoubtedly Order.” This trait was clearly reflected in his extremely methodical and accurate reports, including the data he made available to the public. In 1851, he suggested the location of the Royal Observatory at Greenwich as the location of the Prime Meridian.

One of Airy’s imporant accomplishments was measuring the mean density of the Earth. In 1826 he launched a series of pendulum experiments at the top and bottom of deep mines. In 1854 after several failed efforts due to accidents and flooding, Airy tried the experiment at the Harton pit near South Shields, a coastal town in northeastern England. He was able to show that gravity at the bottom of the mine exceeded that at the top. From this he was led to the final value of Earth's specific density.

In the mid 1840s, Airy’s reputation was tarnished by his hesitancy to search for a planet, whose existence had been predicted by other astronomers, including the French mathematician Urbain Jean Joseph Le Verrier. Le Verrier based his claims only on mathematics and astronomical observations of the known planet Uranus. By the summer of 1846, leading astronomers in France and Germany were systematically searching for the body. Airy resisted joining the race, even after Cambridge astronomer John Couch Adams also predicted that there existed an unobserved planet. On July 9, when Airy finally launched a search, it was too late: the planet Neptune was discovered on September 23, 1846, by Johann Gottfried Galle at the Berlin Observatory. News of the discovery triggered a heated contest over the allocation of credit as well as blame for those who had failed to search more energetically. Airy in particular was severely critized; he wrote later that he “was abused most savagely by the English and French.” He defended himself with the argument that the search for a planet was not the role of the Greenwich Observatory. Moreover, he had actually tried for several months in 1845 and 1846 to convince another British astronomer, James Challis, his successor as Plumian Professor at Cambridge and head of the University Obvservatory, to look for the unseen planet. Finally, some recent scholars have suggested that Airy’s obsession with order and dread of alteration of routine, coupled with a strong sense of duty as a public employee who should not spent taxpayers’ money on such “non-utilitarian” projects, may help explain his reluctance to launch a search.

The “loss to England and to Cambridge of a discovery which ought to be theirs every inch of it,” as the British mathematician and astronomer Sir John Herschel put it in November 1846, cast a long shadow over Airy’s career. Nevertheless, over the course of his life, Airy received numerous awards and honors for his work in mathematics, physics and astronomy. In addition to the Royal Astronomical Society’s Gold Medal, which he won twice, he was awarded the Copley Medal from the Royal Society (1831), and the Lalande Prize from the French Academy of Sciences (1834). He was made a Knights Commander of the Order of the Bath in 1872; shortly afterwards, he was knighted by the Queen.

Airy was married to Richarda Smith. They had nine children, seven of whom survived to adulthood. His son Wilfrid Airy was the designer and engineer for the telescope and its equipment in George Tomline’s Orwell Park Observatory. He edited his father’s autobiography, which was published in 1896, four years after Sir George Biddell Airy’s death.

From the guide to the Sir George Biddell Airy Papers, 1840-1890, (American Philosophical Society)