occupied the
presidential chair of the Royal Society. He devoted himself, _inter
alia_, to optical work, and is perhaps best known by those researches
which deal with the undulatory theory of light. It was on this
subject that he delivered the Burnett lectures in Aberdeen
(1883-1885).

James McCullagh, the son of a poor farmer, was born in Tyrone in
1809, d. 1847. His early death, due to his own hand in a fit of
insanity, cut short his work, but enough remains to permit him to
rank amongst the great mathematicians of all time, his most important
work being his memoir on surfaces of the second order.

Humphrey Lloyd (b. in Dublin 1800, d. 1881), F.R.S. His father was
Provost of Trinity College, Dublin, a position subsequently occupied
also by the son. Lloyd's work was chiefly concerned with optics and
magnetism, and it was in connection with the former that he carried
out what was probably the most important single piece of work of his
life, namely, the experimental proof of the phenomenon of conical
refraction which had been predicted by Sir William Hamilton. He was
responsible for the erection of the Magnetic Observatory in Dublin,
and the instruments used in it were constructed under his observation
and sometimes from his designs or modifications. He was also a
meteorologist of distinction.

George Salmon (b. in Dublin 1819, d. 1904), like the last mentioned
subject, was, at the time of his death, Provost of Trinity College,
Dublin. Besides theological writings, he contributed much to
mathematical science, especially in the directions of conic sections,
analytic geometry, higher plane curves, and the geometry of three
dimensions. He was a Fellow of the Royal Society, and received the
Copley and Royal medals, as well as distinctions from many
universities and learned societies.

John Casey (b. Kilkenny 1820, d. 1891), F.R.S., was educated at a
National School and became a teacher in one in later years. Entirely
self-taught as a mathematician, he raised himself from the humble
position which he occupied to be a university professor (in the
Catholic University of Ireland, and afterwards in the Royal
University), and earned the highest reputation as one of the greatest
authorities on plane geometry. He was a correspondent of eminent
mathematicians all over the world.

Henry Hennessey (b. in Cork 1826, d. 1901), F.R.S., was also a
professor in the Catholic University of Ireland and afterwards in the
Royal College