Sampson, Ralph Allen (1866–1939), astronomer and mathematician, was born 25 June 1866 in Skull (Schull), Co. Cork, fourth among five children of James Sampson (d. 1871), metallurgical chemist and mining engineer from Cornwall, and his wife Sarah Anne (née McDermott). John Sampson (qv) was an elder brother. When Ralph was five years old the family moved to Liverpool and were subsequently impoverished by the combination of a lengthy illness suffered by his father and the failure of the Cornish tin mine industry, in which the family's capital was invested. As a consequence, the boy received little schooling until he started attending the Liverpool Institute at the age of fourteen. In 1884 he entered St John's College, Cambridge, as a sizar, becoming a scholar (1885), graduating as third wrangler (1888), and winning the first Smith's prize (1890), before being elected a fellow of St John's (1890). In 1889 he held a lectureship at King's College, London, and was engaged in hydrodynamical research, until returning to Cambridge in 1891 as the first holder of the newly founded Isaac Newton studentship in astronomy and physical optics. He worked in astronomical spectroscopy under H. F. Newall, publishing a paper (‘On the rotation and mechanical state of the sun’, Memoirs of the Royal Astronomical Society, li (1893), 123–83) that set down postulates for a new theory of the distribution of the sun's internal temperature, stressing the effects of radiation and absorption. That same year (1893) he left Cambridge for the chair of mathematics in the Durham College of Science, Newcastle upon Tyne, but moved on to the University of Durham as professor of mathematics in 1895.
At the Durham observatory Sampson was responsible for the erection of the ‘Durham Almucantor’, a transit instrument in which the transits are taken across a horizontal circle, or almucantor, instead of across the meridian. He also began working on what was to be his greatest contribution to astronomy, the theory and tables of Jupiter's four satellites. The mean motions of the four great satellites of Jupiter had engaged the attention of the great dynamical astronomers of the nineteenth century. By 1900, however, there was great confusion on the issue, as observations of disappearance and reappearance at eclipse were vitiated by many errors. New photometric techniques being used at Harvard permitted more accurate assessment of the progress of an eclipse of a satellite, and the determination, with corresponding precision, of the occurrence of a specific phase. Sampson believed that the Harvard observations warranted a reexamination of the whole question, and began working afresh on the theory. After a detailed and critical study of thousands of observations of eclipses, he published the Tables of the four great satellites of Jupiter (1910), followed by a discussion of the theory, published in the Memoirs of the Royal Astronomical Society, lxiii (1921). For this research he was awarded the gold medal of the Royal Astronomical Society. He also arranged and edited the unpublished papers of his Cambridge tutor, John Couch Adams, published in 1900. He was asked to be editor-in-chief of a complete edition of Isaac Newton's scientific works and correspondence, but the plan eventually fell through.
In 1910 Sampson was appointed professor of astronomy in Edinburgh University and astronomer royal for Scotland. With his interest in astrophysics revived, in conjunction with E. A. Baker he worked out a method of photographic spectrophotometry and designed a recording photo-electric microphotometer. The two men investigated the intensity of radiation from stars over a considerable range of the spectrum, obtaining important results which he described as ‘effective stellar temperatures’ (later known as ‘colour-temperatures’).
Sampson was elected fellow of the Royal Society (1903); the Royal Society of Edinburgh (1911), of which he was a council member and general secretary (1923–33); and the Royal Astronomical Society (1892), where he served as council member (1909–10, 1913–15), vice-president (1918–19), and president (1915–17). He was conferred honorary D.Sc. (Durham) and LLD (Glasgow).
Ill health led to his resignation from the observatory in 1937. After some months travelling abroad, he settled in Bath, and died there 7 November 1939. He married (1893) Ida Binney of St Helen's, Lancashire, and subsequently joined the Society of Friends as a result of her example. He was survived by his wife, a son, and four daughters.