Francis Baily

Francis Baily (28 April 1774Template:Snd30 August 1844) was an English astronomer. He is most famous for his observations of "Baily's beads" during a total eclipse of the Sun. Baily was also a major figure in the early history of the Royal Astronomical Society, as one of the founders and as the president four times.

Life

Baily was born at Newbury in Berkshire in 1774 to Richard Baily.<ref>Template:Cite book</ref> 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, Baily 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.<ref name="EB1911">Template:EB1911 This also cites

• J. Herschel's Memoir of F. Baily, Esq. (1845), also prefixed to Baily's Journal of a Tour, with a list of his writings (see Further reading).
• Month. Not. R. Astr. Soc. xiv. 1844.</ref>

Astronomical work

File:Baily, Francis – On the new method of determining the longitude by the culmination of the moon and stars, 1824 – BEIC 720900.jpg

On the new method of determining the longitude by the culmination of the moon and stars, 1824

By 1820, Baily had already taken a leading part in the foundation of the Royal Astronomical Society,<ref name=dreyer/> and he received its Gold Medal in 1827<ref name=gold_medal>Template:Cite web</ref> for his preparation of the Society's Catalogue of 2881 stars (Memoirs R. Astr. Soc. ii.).<ref name="EB1911"/> Later, in 1843, he would win the Gold Medal again.<ref name=gold_medal/> He was elected as President of the Royal Astronomical Society four times, with two-year terms each (1825–1827, 1833–1835, 1837–1839 and 1843–1845).<ref name=dreyer>Template:Cite bookTemplate:Page needed</ref>Template:Page needed<ref name="Royal Astronomical Society">Template:Cite web</ref> No other person has served in the position more than Baily's four times (a record he shares with George Airy), whilst his eight years in the post are a record.<ref name="Royal Astronomical Society"/>Template:Page needed

The reform of the Nautical Almanac in 1829 was set on foot by his protestsTemplate:Discuss. He was elected a Foreign Honorary Member of the American Academy of Arts and Sciences in 1832.<ref name=AAAS>Template:Cite web</ref> 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 57,000Template:Cn stars; he superintended the compilation of the British Association's Catalogue of 8377 stars (BAC, published 1845);<ref>Template:Cite web</ref> and revised the catalogues of Tobias Mayer, Ptolemy, Ulugh Beg, Tycho Brahe, Edmund Halley and Hevelius (Memoirs R. Astr. Soc. iv, xiii.).<ref name="EB1911"/>

His observations of "Baily's Beads", during an annular eclipse of the Sun on 15 May 1836, at Inch Bonney in Roxburghshire, started the modern series of eclipse expeditions. The phenomenon, which depends upon the irregular shape of the Moon's limb, was so vividly described by him as to attract an unprecedented amount of attention to the total eclipse of 8 July 1842, observed by Baily himself at Pavia.<ref name="EB1911"/>

File:August 21 2017 solar eclipse baily beads TLR2.jpg

Baily's beads four seconds before totality (August 21, 2017)

In other work, 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.). This value was corrected for the length of the seconds-pendulum by introducing a neglected element of reduction, and was used, in 1843, in the reconstruction of the standards of length. His laborious operations for determining the mean density of the Earth, carried out by Henry Cavendish's method (1838–1842), yielded the authoritative value of 5.66.<ref name="EB1911"/>

Baily died in London on 30 August 1844 and was buried in the family vault in St Mary's Church in Thatcham, Berkshire. His 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.<ref name="EB1911"/>

The lunar crater Baily was named in his honour, as was the rigid and thermally insensitive alloy used to cast the 1855 standard yard (Baily's metal, 16 parts copper, 2.5 parts tin, 1 part zinc), and a local primary school in the town of Thatcham (Francis Baily CofE Primary School).Template:Citation needed

Further reading

• Template:Cite encyclopedia
• Template:Cite journal
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External links

• Template:Wikisource author-inline
• Template:Cite DNB
• Map of Etoiles fixes
• British Association Catalogue of 8377 Stars
• Awarding of RAS gold medal, 1827: MNRAS 1 (1827) 14
• Awarding of RAS gold medal, 1843: MNRAS 5 (1843) 248
• Template:UK National Archives ID