Baily, Francis

(b. Newbery, Berkshire, England, 28 April 1774; d. London, England, 30 August1844)

astronomy, metrology.

Baily was one of the founders of the Astronomical Society of London (later the Royal Astronomical Society). His enthusiasm and organizing ability served to arouse interest in astronomy and to put its practical aspects on a firm footing. Today he is remembered (although frequently with his name misspelled) for “Baily’s beads,” an effect seen during solar eclipses by many men before Baily but never so vividly described.

Baily, the third son of a banker, received only an elementary education. At the age of fourteen he was apprenticed to a London mercantile firm. As soon as his seven years of apprenticeship were up, Baily set sail for the United States and two years of rugged adventures at sea and in the backwoods, which he described in his Journal. He returned to England in 1798, hoping to spend his life as an explorer. When all efforts to obtain backing for such a career proved fruitless, he became a stockbroker instead. Before the end of the Napoleonic wars he had published several actuarial tables, An epitome of Universal History, and an astronomical paper (1811).

Having prospered on the stock exchange, Baily retired at the age of fifty to devote his full time to astronomy he had become a fellow of the Royal Society in 1921 and was to serve the Astronomical Society as president during four two-year terms, the first beginning in 1825 and the last interrupted by his death.

Baily’s first substantial astronomical work dealt with methods of determining latitude and time by the stars. Since no up-to-date star catalog was available for this purpose, Baily calculated the mean positions of 2,881 stars for the epoch 1 January 1830; this work, published in 1826, earned him his first Gold Medal from the Astronomical Society. (The second came in 1843, for his redetermination of the density of the earth.)

Work on the standard pendulum, the standard yard, and the ellipticity of the earth followed, interspersed among revisions of many star catalogs. In the course of preparing a new edition of the Historica coelestis of 1712, Baily found and published (1835) evidence that Edmund Halley, the second astronomer royal, had unduly maligned his predecessor, John Flamsteed.

It was during the annular eclipse of 15 May 1836, which he observed from Inch Bonney in Scotland, that Baily first saw the “beads.” They are a transient phenomenon often seen at the beginning and end of totality in a solar eclipse, when the edge of the moon is close to inner tangency and a thin crescent of sunlight shines between mountains on the moon’s limb. In Baily’s own words, they appear as “a row of lucid points, like a string of bright beads … running along the lunar disc with beautiful coruscations of light.”His report (1838) included a list of all previous observers, beginning with Halley in 1715, and aroused keen interest. For the solar eclipse of 8 July 1842, many astronomers accordingly journeyed to Italy, where the eclipse was to be total. The British astronomer royal, George B. Airy, who was in Turin, looked for, but did not see, “Mr. Baily’s beads”; Baily himself, in Pavia, did see them but only at the beginning of totality (1846).

BIBLIOGRAPHY

I. Original Works. Baily’s works mentioned in the text are Tables for the Purchasing and Renewing of Leases for Terms of Years Certain and for Lives (London, 1802; 3rd ed., 1812); The Doctrine of Life-Annuities and Assurances Analytically Investigated (London, 1810; appendix 1813); “On the Solar Eclipse Said to Have Been Predicted by Thales,” in Philosophical Transactions of the Royal Society, 101 (1811), 220-241; An Epitome of Universal History, 2 vols. (London, 1813); “On the Construction and Use of Some New Tables for Determining the Apparent Places of Nearly 3000 Principal Fixed Stars,” in Memoirs of the [Royal] Astronomical Society of London, 2 (1826), whole appendix: Baily’s Preface iii-xli, auxiliary tables xlii-liv. the general catalog lv-ccxxi, supplementary tables ccxx-ccxxiii, errata ccxxiv; An Account of the Revd. John Flamsteed, the First Astronomer Royal (London, 1835; facsimile reprint, omitting the star catalog, London, 1966); “On a Remarkable Phenomenon that Occurs in Total and Annular Eclipses of the Sun,” in Memoirs of the Royal Astronomical Society, 10 (1838), 1-42; “Some Remarks on the Total Eclipse of the Sun on July 8th, 1842,” ibid., 15 (1846), 1-8.

Ninety-one publications are listed in the preface to Baily’s travel diary, Journal of a Tour in Unsettled Parts of North America in 1796 and 1797, Augustus de Morgan, ed. (London, 1856), pp. 61-69; fifty appear in the Royal Society of London’s Catalogue of Scientific Papers, I (London, 1867), 158-160. Baily’s long articles constitute the bulk of the first fifteen volumes of the Memoirs of the [Royal) Astronomical Society of London (1822-1846)-his edition of Tobias Mayer’s star catalog in 4 (1831), 391-445; of the Abbe de La Caille’s catalog in 5 (1833), 93-124; of the catalogs of Ptolemy, Ulugh Beigh, Tycho Brahe, Halley, and Hevelius in 13 (1843), prefaces 1-48, tables(1)-(248), with errata facing p. 1; his work on the earth’s ellipticity in 7 (1834), 1-378; on the standard yard in 9(1836), 35-184; and on the earth’s density in 14 (1843), 1-120 with tables on i-ccxlvii. His paper on correcting a pendulum to vacuum is in Philosophical Transactions of the Royal Society of London, 122 (1832), 399-492. Three more star catalogs were completed and published posthumously: a revision of Jérôme Lalande’s Histoire celeste fiançaise and of La Caille’s southern hemisphere stars (both London, 1847) and finally the ultimate evidence of Baily’s industry, the British Association for the Advancement of Sciences’ catalog of almost 10,000 stars (London, 1845).

II. Secondary Literature. Baily’s entry in Dictionary of National Biography, II (London, 1885), 427-432, written by Agnes M. Clerke, includes an appraisal of his achievements. An obituary by Sir John Herschel appeared in Philosophical Magazine (London), ser. 3, 26 (1845), 38-75, and was reprinted, with additions, as part of the preface to Baily’s Journal.

Sally H. Dieke