Francis Baily

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For the American lawyer, see Francis Bailey

Francis Baily (April 28, 1774 – August 30, 1844), English astronomer, was born at Newbury, Berkshire.

After a tour in the unsettled parts of North America in 1796–1797, his journal of which was edited by Augustus de Morgan in 1856, he entered the London Stock Exchange in 1799. The successive publication of Tables for the Purchasing and Renewing of Leases (1802), of The Doctrine of Interest and Annuities (1808), and The Doctrine of Life-Annuities and Assurances (1810), earned him a high reputation as a writer on life-contingencies; he amassed a fortune through diligence and integrity and retired from business in 1825, to devote himself wholly to astronomy.

He had already, in 1820, taken a leading part in the foundation of the Royal Astronomical 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.). Later in 1843 he would win the Gold Medal again.

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 catalogues containing about 57,000 stars; he superintended the compilation of the British Association's Catalogue of 8377 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 observations 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 attention to the totality of July 8, 1842, observed by Baily himself at Pavia.

He completed and discussed H. Foster's pendulum experiments, deducing from them an ellipticity for the earth of 1/289.48 (Memoirs R. Astr. Soc. vii.); corrected for the length of the seconds-pendulum by introducing a neglected element of reduction; 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 (1838–1842), yielded for it the authoritative value of 5.66.

He died in London, on August 30, 1844 and was buried in the family vault in Thatcham parish church. Baily's Account of the Rev. John Flamsteed (1835) is of fundamental importance to the scientific history of that time. It included a republication of the British Catalogue.

The lunar crater Baily was named in his honour.