Humphrey Lloyd FRS FRSE PRIA (16 April 1800 – 17 January 1881) was an Irish physicist and academic who served as the 30th Provost of Trinity College Dublin from 1867 to 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.

[1][2] Humphrey carried out the Lloyd's mirror optic experiments, and was a member of numerous societies in Europe and North America.

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.

)[3] 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 the committee of the British Association lobbying government to improve knowledge of terrestrial magnetism by establishing observing stations.

He was president of the British Association in 1857, when it met in Dublin, and delivered an inaugural address, which was published, in which he gave a sketch of the recent progress made in astronomy, terrestrial magnetism, and other branches of science.

Papers which he wrote on terrestrial magnetism and other subjects are in the Reports of the British Association and in the Transactions and Proceedings of the Royal Irish Academy.