Mary Fairfax, daughter of William George Fairfax (1739-1813) and Margaret Charters (1741-1832), was born in Jedburgh in 1780. She grew up in Burntisland, Fife. Though she received little formal education, she was helped by her uncle, Rev. Thomas Somerville, to learn Latin, and she read mathematics independently. In 1804 Mary married Samuel Greig (1777/8-1807), who served as commissioner for the Russian navy and Russian vice-consul in London. They had two sons, Woronzow (1805-1865) and William George (1807-1814). Mary continued her studies in London. She returned to Scotland in 1807 on the death of her husband. There she received tuition in mathematics from William Wallace, later professor of mathematics at Edinburgh University, and his brother, John.

In 1812 Mary married William Somerville (1771-1860), an army doctor and her cousin, son of Rev. Thomas Somerville and Martha Charters. Four years later Mary, William and their daughters, Martha Charters and Mary Charlotte, moved to London, where Mary furthered her knowledge through correspondence and meetings with many of the leading scientific figures of the time. The astronomer, J.F.W. Herschel, was to become an especially valued friend and adviser.

Mary began to publish in 1826, with a report of observations on the magnetizing power of sunlight. In 1827 she was asked by Henry Brougham, later 1st Baron Brougham and Vaux, Lord Chancellor, to prepare an English version of Laplace's Mécanique Céleste (1797-1827). The Mechanism of the Heavens was published by John Murray in 1831. The next year, Preliminary Dissertation to the Mechanism of the Heavens appeared. Later works by Mary, some of which ran to many editions, were On the Connexion of the Physical Sciences (1834), Physical Geography (1848) and On Molecular and Microscopic Science (1869). Her autobiography, Personal Recollections, from Early Life to Old Age, was published posthumously in 1873.

In 1838 the Somervilles moved to Rome for the winter. They remained in Italy thereafter. Mary died in Naples on 29 Nov 1872. She had received many honours during her lifetime, and after her death, Somerville College, Oxford, founded in 1879 as a women's college, was named after her. A Somerville scholarship for women also commemorates her name.

For further information see Oxford Dictionary of National Biography