Bertha Swirles was born in Northampton, the daughter of William Alexander Swirles and Harriett Blaxley. She was educated at Northampton School for Girls and came up to Girton College in 1921 to read Mathematics. She was awarded her PhD in 1929. A fellow research student was Douglas Hartree, who became a lifelong friend. She lectured successively in Manchester, Bristol, Imperial College London and Manchester before returning to Cambridge and Girton in 1938 to take up a Fellowship and Lectureship in Mathematics. She remained at Girton for the rest of her career: amongst a number of College offices, she served as Director of Studies in Mathematics and Mechanical Sciences for many years; she was also Director of Studies in Music for a number of years; she was Treasurer of the Girton Working Women’s Summer School; and she was Vice-Mistress from 1966 to 1969. She was appointed a Life Fellow of Girton in 1969. In 1940, Bertha Swirles married Harold Jeffreys (later appointed Plumian Professor of Astronomy at Cambridge and knighted in 1953). Her collaboration with him led to their co-authorship of Methods of Mathematical Physics, first published in 1946 and revised and reprinted for well over fifty years. Bertha Jeffreys died on 18 December 1999. A fuller biography, compiled for St John's College Cambridge by Timothy E Powell and Peter Harper of the National Cataloguing Unit for the Archives of Contemporary Scientists, can be found on the Janus website under St John's College Library, JeffreysB.