Humphrey Lloyd FRS FRSE MRIA (1800–1881) was an Irish physicist. He was Erasmus Smith's Professor of Natural and Experimental Philosophy at Trinity College Dublin (1831-1843) and much later Provost (1867–1881). Lloyd is known for experimentally verifying conical refraction, a theoretical prediction made by William Rowan Hamilton about the way light is bent when travelling through a biaxial crystal. He was a Fellow of the Royal Society, and President of both the British Association and the Royal Irish Academy. Early life The eldest son of the Rev. Bartholomew Lloyd, and his wife, Eleanor McLaughlin, he was born in Dublin on 16 April 1800. His father had also served as Erasmus Smith's Professor of Natural and Experimental Philosophy and Provost of TCD. After early education at Mr. White's school in Dublin, he entered Trinity College Dublin in 1815, first out of 63 competitors in the entrance examination. He was elected a Scholar in 1818, and graduated B.A. in 1819, taking first place and the gold medal for science, and proceeding M.A. in 1827, and D.D. in 1840. He became a junior fellow in 1824, and a senior fellow in 1843. Scientific career Lloyd in 1831 succeeded his father as Erasmus Smith's Professor of Natural and Experimental Philosophy. At the meeting of the British Association in 1833 he spoke on his establishment by experiment of the existence of conical refraction in biaxial crystals, in conformity with the theory of William Rowan Hamilton. He also succeeded in establishing experimentally the law by which the polarisation of the rays composing the luminous cone is governed. Shortly after, by means of an experiment on the interference of light proceeding directly from a luminous source, with light coming from the same source but reflected at a very high angle of incidence from a plane surface, he contributed to the theory of reflected light. A letter from Sir David Brewster led him to turn his attention to the phenomena of light incident on thin plates. In 1841 he submitted a communication on the subject to the British Association, and in 1859 he described his investigation of the phenomena to the Royal Irish Academy (see Transactions, vol. xxiv.) When the magnetic observatory of Trinity College Dublin, was established under the auspices of his father, it was placed in Lloyd's charge, and the instruments for it were devised by him and constructed under his superintendence. He was a member of