Monck, William Henry Stanley (1839–1915), philosopher and astronomer, was born 21 April 1839 at Skeirke, Queen's Co. (Laois), third son of Thomas Stanley Monck, curate of Skeirke 1829–50, and Lydia Elinor Monck (née Kennedy). The family moved (1850) to Inistioge, Co. Kilkenny, where Thomas Monck was rector until his death (1858). William's grandfather was a younger brother of Charles Stanley Monck, 1st Viscount Monck. William was mainly self-educated, though for a time he was taught by tutors at home. At TCD he won the first scholarship in science with a gold medal and a senior moderatorship in logic and ethics (1861), as well as the Wray prize for the encouragement of metaphysical studies. His first works include The Christian miracles (1863) and The revival of philosophical scepticism (1868), the latter published under the pseudonym of ‘Davidson Hume’. His Space and vision (1872) was regarded as a useful contribution to the philosophical understanding of perception; he did not accept the associationist theory proposed by followers of George Berkeley (qv), and though well versed in Kant's work, disagreed with some aspects of it. After initially intending to become a clergyman, he decided on law, entered King's Inns (1869), and was called to the bar (1873). He pursued this profession with some success and was later appointed chief registrar in the bankruptcy division of the high court. However, he returned to academic life in 1878 when he was appointed professor of moral philosophy in TCD, a position he held until 1882. During this period he wrote student textbooks, including An introduction to logic (1880) and a biography, Sir William Hamilton (1881).
Throughout his life Monck retained an interest in astronomy, and was a frequent correspondent to journals such as the Astrophysical Journal, the Journal of the British Astronomical Association, and Observatory. In 1886 he was elected a fellow of the Royal Astronomical Society. In July 1890 he wrote a letter to the English Mechanic, in which he advocated the formation of an association of amateur astronomers for those excluded from the socially elite Royal Astronomical Society, which also refused membership to women. This letter contributed to the foundation of the British Astronomical Association in October 1890 and Monck was a member of its first council. In October 1885 he published a paper on the ‘Distribution of stars in space’ in the Scientific Proceedings of the Royal Dublin Society. In 1890 he purchased an Alvan Clark 7.5 in. (19.05 cm) refracting telescope and set it up in a small observatory at his home at 16 Earlsfort Terrace. In 1892 his friend George M. Minchin (qv) developed a technique for making photo-voltaic cells using selenium, and in early August brought some of the cells to Dublin in order to try to use them to detect and measure starlight. Because of unfavourable weather, the tests were abandoned and Minchin returned to London. However, Monck, along with his neighbour Stephen Dixon, tested the cells on 28 August 1892. The experiment was a modest success and small but definite measurements were recorded for Jupiter and Venus. This was the first electrical detection of starlight.
That same year Monck published a paper suggesting the luminosity of stars varied with spectral type. He found an unexpected correlation between the distances and colours of stars, namely that in general yellow stars appeared nearer than either blue or red stars. This anticipated the researches of Hertzsprung and Russell in the early part of the twentieth century on the relationship between magnitude and the spectral type of stars. In 1894 Monck suggested that there were two distinct classes of yellow stars: those that were dull and near and those that were bright and remote. As a result of Monck's insight, John Ellard Gore (qv) estimated that the star Arcturus had a diameter almost eighty (actually twenty-eight) times larger than the sun. However, Monck's researches were eclipsed about 1910 by the findings of Hertzsprung and Russell, which were based on accurate photographic parallaxes not available to Monck. In 1899 he published An introduction to stellar astronomy; in it he first proposed the unit of distance later known as the parsec (p. 51).
He died 24 June 1915 and was survived by his wife Catherine, a daughter of Tobias Peyton of Co. Roscommon; they had no children. A plaque to honour the location of the first electric measurements of starlight was unveiled at 16 Earlsfort Terrace on 6 April 1987.