As Astronomer Royal he seems to have inherited and summed up all the great qualities of his predecessors: Flamsteed's methodical habits and unflagging industry; Halley's interest in the lunar theory; Bradley's devotion to star observation and catalogue making; Maskelyne's promptitude in publishing, and keen interest in practical navigation; Pond's refinement of observation. Nor did he allow this inheritance to be merely metaphorical; he made it an actual reality. He discussed, reduced, and published, in forms suitable for use and comparison to-day, the whole vast mass of planetary and lunar observations made at the Royal Observatory from the year 1760 to his own accession, a work of prodigious labour, but of proportionate importance. Airy has been accused—and with some reason—of being a strong, selfish, aggressive man; yet nothing can show more clearly than this great work how thoroughly he placed the fame and usefulness of the Observatory before all personal considerations. With far less labour he could have carried on a dozen investigations that would have brought him more fame than this great enterprise, the purpose of which was to render the work of his predecessors of the highest possible use. The light in which he regarded his office may best be expressed in his own words:—
'The Observatory was expressly built for the aid of astronomy and navigation, for promoting methods of determining longitude at sea, and (as the circumstances that led to its foundation show) more especially for determination of the moon's motions. All these imply, as their first step, the formation of accurate catalogues of stars, and the determination of the fundamental elements of the solar system. These objects have been steadily pursued from the foundation of the Observatory; in one way by Flamsteed; in another way by Halley, and by Bradley in the earlier part of his career; in a third form by Bradley in his later years; by Maskelyne (who contributed most powerfully both to lunar and to chronometric nautical astronomy), and for a time by Pond; then with improved instruments by Pond, and by myself for some years; and subsequently, with the instruments now in use. It has been invariably my own intention to maintain the principles of the long-established system in perfect integrity; varying the instruments, the modes of employing them, and the modes of utilizing the observations of calculation and publication, as the progress of science might seem to require.'
The result of this keen appreciation of the essential continuity of the Astronomer Royalship has been that it is to Airy, more than to any of his predecessors, or than to all of them put together, that the high reputation of Greenwich Observatory is due. Professor Newcomb, the greatest living authority on the subject outside our own land—and other great foreign astronomers have independently pronounced the same verdict—has said:—
'The most useful branch of astronomy has hitherto been that which, treating of the positions and motions of the heavenly bodies, is practically applied to the determination of geographical positions on land and at sea. The Greenwich Observatory has, during the past century, been so far the largest contributor in this direction as to give rise to the remark that, if this branch of astronomy were entirely lost, it could be reconstructed from the Greenwich observations alone.'
Early in 1836 Airy proposed to the Board of Visitors the creation of the Magnetic and Meteorological department of the Observatory, and in 1840 a system of regular two-hourly observations was set on foot. This was the first great enlargement of programme for the Observatory beyond the original one expressed in Flamsteed's warrant. It was followed in 1873 with the formation of the Solar Photographic department, to which the Spectroscope was added a little later.
Though he had objected strongly on his first coming to the Observatory to the excessive time devoted to the merely commercial side of the care of chronometers, yet the perfecting of these instruments was one that he had much at heart, and many recent appliances are either of his own invention or are due to suggestions which he threw out.
Much work lying outside the Observatory, and yet intimately connected with it, was carried out either by him or in accordance with his directions. The transit of Venus expeditions of 1874, the delimitation of the boundary line between Canada and the United States, and, later, that of the Oregon boundary; the determination of the longitudes of Valencia, Cambridge, Edinburgh, Brussels, and Paris; assistance in the determination of the longitude of Altona—all came under Airy's direction. Nor did he neglect expeditions in connection with what we would now call the physical side of astronomy. On three occasions, 1842, 1851, and 1860, he himself personally took part in successful eclipse expeditions. The determination of the increase of gravity observable in the descent of a deep mine was also the subject of another expedition, to the Harton Colliery, near South Shields.
But with all these, and many other inquiries—for he was the confidential adviser of the Government in a vast number of subjects: lighthouses, railways, standard weights and measures, drainage, bridges—he yet always kept the original objects of the Observatory in the very first place. It was in order to get more frequent observations of the moon that he had the altazimuth erected, which was completed in May, 1847. This was followed, in 1851, by the transit circle, as he had long felt the need for more powerful light grasp in the fundamental instrument of the Observatory. The transit circle took the place both of the old transit instrument and of the mural circle. Above all, he arranged for the observations of moon and stars to be carried out with practical continuity. The observations were made and reduced at once, and published in such a way that any one wishing to discuss them afresh could for himself go over every step of the reduction from the commencement, and could see precisely what had been done.