Page:Dictionary of National Biography. Sup. Vol I (1901).djvu/85

  [q. v.] as Plumian professor of astronomy and director of the Cambridge observatory. His income was now augmented to 500l. a year, and thus provided for, he succeeded in inducing Richarda Smith to marry him on 24 March 1830. At the observatory he introduced an improved system of meridian observations, afterwards continued at Greenwich and partially adopted abroad, and set the example of thoroughly reducing before publishing them. He superintended besides the erection of several instruments, and devised the equatorial mount for the Cauchoix twelve-inch lens, which was presented in 1833 to the institution by the Duke of Northumberland. In February 1835 Sir Robert Peel offered Airy a civil-list pension of 300l. a year, which, by his request, was settled on his wife; and on 18 June 1835 he accepted the post of astronomer royal, for which Lord Melbourne designated him in succession to [q. v.]

Airy's tenure of the office of astronomer-royal lasted forty-six years, and was marked by extraordinary energy. He completely re-equipped the Royal Observatory with instruments designed by himself. The erection in 1847 of an altazimuth for observing the moon in every part of the sky proved of great importance for the correction of lunar tables. A new transit circle of unprecedented optical power and mechanical stability was mounted in 1851, and a reflex zenith tube replaced Troughton's zenith sector in the same year. The inauguration in 1859 of a thirteen-inch equatorial by Merz finished the transforming process. Its use the astronomer royal was resolved should never interfere with the 'staple and standard work' of the establishment; yet, while firmly adhering to the meridional system prescribed 'by both reason and tradition,' he kept well abreast of novel requirements. In 1838 he created at Greenwich a magnetic and meteorological department, Brooke's plan of photographic registration being introduced in 1848. From 1854 transits were timed by electricity; spectroscopic observations were organised in 1868, and the prismatic mapping of solar prominences in 1874; while with the Kew heliograph a daily record of sunspots was begun in 1873. Meantime Airy accomplished the colossal task of reducing all the planetary and lunar observations made at Greenwich between 1750 and 1830, for which he received the gold medal of the Royal Astronomical Society in 1846, and an equivalent testimonial in 1848. The mass of materials thus provided was indispensable to the progress of celestial mechanics.

Airy observed the total solar eclipse of July 1842 from the Superga, near Turin (Memoirs of Roy. Astr. Society, vol. xv.), and that of 28 July 1851 from Gothenburg in Sweden (ib. vol. xxi.) He subsequently visited Upsala, was received in audience by King Oscar at Stockholm, and on the return journey inspected the pumping-engines at Haarlem. For the Spanish eclipse of 18 July 1860 he organised a cosmopolitan expedition, which he conveyed to Bilbao and Santander in the troopship Himalaya, placed at his disposal by the admiralty. He fixed his own station at Herena, but was disappointed in the result. In the autumn of 1854 he superintended an elaborate series of pendulum-experiments for the purpose of measuring the increase of gravity with descent below the earth's surface. Similar attempts made by him in the Dolcoath mine, Cornwall, in 1826 and 1828, with the co-operation of [q. v.] and [q. v.], had been accidentally frustrated. He now renewed them in the Harton colliery, near South Shields, at a depth of 1,260 feet. The upshot was to give 6·56 for the mean density of the earth (Phil. Trans. cxlvi. 342), a value considerably too high. Airy explained the method in a popular lecture at South Shields.

The preparations for the transit of Venus in 1874 cost him enormous labour. The entire control of the various British expeditions was in his hands; he provided twenty-three telescopes, undertook the preliminary work at the observatory, and the subsequent reduction of the vast mass of collected data. The volume embodying them was issued in 1881. Incredible industry and high business capacity alone enabled him to discharge the miscellaneous tasks imposed upon him. He acted as chairman and working secretary of the commission of weights and measures (1838-1842), sat on the tidal harbour and railway gauge commissions in 1845, on the sewers commission in 1848, on the exchequer standards and the coinage commissions in 1868. He experimented in 1838 on the correction of compasses in iron ships, devising the principle still in use; contributed energetically to the improvement of lighthouses, aided in the delimitation of the Maine and Oregon boundaries, and settled the provisions for the sale of gas. The reduction of tidal observations in Ireland and India, and the determination in 1862 of the difference of longitude between Valencia, co. Kerry, and Greenwich, engaged his strenuous attention. He was consulted about the launch of the Great Eastern, the laying of the Atlantic cable, Babbage's calculating machine, the chimes of Westminster clock, and the smoky