BAILY, FRANCIS (1774-1844), English astronomer, was born at Newbury, Berkshire. He made a fortune on the Stock Exchange, and acquired a great reputation for his actuarial cal culations. He retired from business in 1825. He had already, in 1820, taken a leading part in the foundation of the Royal Astro nomical Society; and its gold medal was awarded him in 1827, for his preparation of the Astronomical Society's Catalogue of 2881 stars (Memoirs R. Astr. Soc. ii.). The reform of the Nautical Almanac in 1829 was set on foot by his protests; he recommended to the British Association in 1837, and in great part executed, the reduction of Joseph de Lalande's and Nicolas de Lacaille's cata logues containing about 57,000 stars; he superintended the com pilation of the British Association's Catalogue of 8,3 77 stars (published 1845) ; and revised the catalogues of Tobias Mayer, Ptolemy, Ulugh Beg, Tycho Brahe, Edmund Halley and Hevelius (Memoirs R. Astr. Soc. iv., xiii.).
His notice of "Baily's Beads," during an annular eclipse of the sun on May 15, 1836, at Inch Bonney in Roxburghshire, started the modern series of eclipse-expeditions. The phenomenon, which depends upon the inequalities of the moon's limb, was so vividly described by him as to attract an unprecedented amount of atten tion to the totality of July 8, 1842, observed by Baily himself at Pavia. He completed and discussed H. Foster's pendulum-experi ments, deducing from them an ellipticity for the earth of (Memoirs R. Astr. Soc. vii.) ; corrected for the length of the seconds-pendulum by introducing a neglected element of reduc tion ; and was entrusted, in 1843, with the reconstruction of the standards of length. His laborious operations for determining the mean density of the earth, carried on by Henry Cavendish's method (1838-42), yielded for it the authoritative value of 5.66. Baily's Account of the Rev. John Flamsteed (183 5) is of funda mental importance to the scientific history of that time. It in cluded a republication of the British Catalogue.
See J. Herschel's Memoir of F. Bally, Esq. (1845), also prefixed to Baily's Journal of a Tour, with a list of his writings; Month. Not. R. Astr. Soc. xiv.