Lloyd, Humphrey (1800–81), scientist and provost of TCD, was born 16 April 1800 in Dublin, eldest son of the Rev. Bartholomew Lloyd (qv), then a fellow and later provost of TCD, and Eleanor Lloyd (née McLaughlin). Initially educated at White's school, Dublin, he came first in the entrance examination for TCD in 1815, entering the college on 3 July. Throughout his student career he displayed great ability and was awarded a scholarship in 1818. He graduated BA in 1820, winning a gold medal for scientific achievement. Appointed junior fellow (1824), he graduated MA in 1827. In 1831 he succeeded his father as professor of natural and experimental philosophy (1831–43) and, following theological studies, graduated BD and DD (1840).
He was destined to surpass his father's impressive scientific record, and published widely. On taking up the professorship he began researches in the field of optical science, contributing to the theories on reflected light and also on the wave theory of light. At a meeting of the British Association (1833) he delivered an account of how he had established by experiment the existence of conical refraction in biaxial crystals. This has been viewed as the most important scientific discovery of his career and, as a prominent member of the British Association and the RIA, he soon became a leading figure in scientific circles in Dublin and London. Placed in charge of the magnetic observatory in TCD, he supervised its construction and designed its instruments. He then became involved in a project being organised under the auspices of the British Association and the Royal Society; this planned to establish a number of magnetic observatories in Britain and India and then begin a programme of observations. Lloyd wrote recommendations on how these observatories should be operated and also trained the staff who would eventually man them.
In April 1841 he and two other members of the TCD staff, James MacCullagh (qv) and Thomas Luby (qv), sent a memorandum to the board of the college, recommending the establishment of a school of civil engineering. This school was established at the end of Trinity term 1841, making TCD one of the first colleges to teach civil engineering. Resigning his chair (1843), he was appointed as a senior fellow and was considered for the provostship in 1851. Elected president of the RIA (1846–51), he was awarded the academy's Cunningham gold medal in 1862; he was appointed vice-provost in the same year and elected provost in 1867. Like his father, he instituted a programme of reforms and was notable for advocating research as a function of the college. Although a noted scientist, he had a great love for the classics and tried to foster further classical studies at TCD. He was also noted for his opposition to the attempts of Henry Fawcett to have the test acts abolished in the University of Dublin.
During the course of his career the numerous honours awarded to him included an honorary doctorate from the University of Oxford (1855). A fellow of the Royal Societies of London and Edinburgh, in 1874 he was awarded the German order Pour le Mérite by the emperor William I for his scientific achievements. His many publications include A treatise on light and vision (1831), Lectures on the wave-theory of light (2 vols, 1836, 1841), and The elements of optics (1849). He also published a large number of scientific articles in journals such as Proceedings of the Royal Society, Transactions of the Royal Irish Academy, and Report of the British Association. In 1825 and 1826 he published articles in the Dublin Philosophical Journal and Scientific Review. He died 17 January 1881 in Dublin.
He married (July 1840) Dorothea Maria Redfoord, daughter of the Rev. James Bulwer; they had no children. There is a bust of Lloyd, by Albert Bruce-Joy (qv), in TCD's Old Library. The TCD manuscripts library has a large collection of his papers.