Three times (viz., in 1842, 1851, and 1860) has he visited the Continent for the purpose of observing different solar eclipses; and on the last-named occasion he organised an expedition of English and foreign astronomers to Spain, which is known as the "Himalayan Expedition," from the name of the ship lent for the purpose by the Admiralty. Sir G. B. Airy has illustrated the Newtonian theory of gravitation, and approximated the great object of ascertaining the weight of the earth, by a series of experiments on the relative vibrations of a pendulum at the top and at the bottom of a deep mine (the Harton Colliery, near South Shields); has paid great attention to the testing and improvement of marine chronometers; and to the diffusion, by galvanic telegraph, of accurate time-signals. In 1838 he was consulted by the Government respecting the disturbance of the compass in iron-built ships, and the result of the experiments and theory developed by him on that occasion was the establishment of a system of mechanical correction by means of magnets and iron, which has since been adopted universally. He was chairman of the Commission appointed to consider the general question of standards, and of the Commission intrusted with the superintendence of the construction of new Standards of Length and Weight, after the great fire which destroyed the former national standards in the Houses of Parliament in 1834. The account of the proceedings on these occasions, published in the "Philosophical Transactions," is from his pen. He advocated the establishment of a decimal coinage and, acting as one of three Royal Commissioners on Railway Gauge, recommended the narrow as opposed to the broad gauge on our railways; conducted the astronomical operations preparatory to the definition of the boundary between Canada and the United States, and aided in tracing the Oregon boundary. Sir G. B. Airy contributed to the "Cambridge Transactions," "The Philosophical Transactions," "The Memoirs of the Royal Astronomical Society," the Philosophical Magazine, and the Athenæum (often under the signature of A.B.G.). In the Athenæum are several papers on antiquarian subjects, especially British. He also wrote strongly in the Athenæum and elsewhere in opposition to the legislation proposed by the University Commissioners in reference to his own university, and more especially to his own college. In 1869 he communicated a remarkable discovery to the Royal Astronomical Society, in a "Note on Atmospheric Chromatic Dispersion, as affecting Telescopic Observation, and on the Mode of Correcting it." He was intrusted with the entire direction of the British portion of the enterprise for observing the Transit of Venus in Dec. 1874; on the results of which a Report was communicated to the House of Commons in 1877. More recently he has suggested a new method of treating the Lunar Theory. He added to the original course of labours at the Royal Observatory a very complete system of magnetic, meteorological, photoheliographic, and spectroscopic observations. The principal works written by Sir G. B. Airy are, "Gravitation," for the Penny Cyclopædia, published separately; also, "MathematicalTracts" (fourth edition), "Ipswich Lectures on Astronomy" (fourth edition), "Treatise on Errors of Observation" (1861), "Treatise on Sound" (1869), "Treatise on Magnetism" (1870); also "Trigonometry," "Figure of the Earth," and "Tides and Waves," in the Encyclopædia Metropolitana, since republished separately; and "Notes on the early Hebrew Scriptures." Sir G. B. Airy has received the Lalande medal of the French Institute, for discoveries in
