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James MacCullagh

James MacCullagh
James MacCullagh (1809–1847)
Born 1809
Landahaussy, Ireland
Died 24 October 1847
Nationality Irish
Fields Physics
Known for Theory of elasticity
Notable awards Copley Medal (1842)

James MacCullagh (1809 – 24 October 1847) was an Irish mathematician.

Life and work

MacCullagh was born in Landahaussy, near Plumbridge, County Tyrone, Ireland, but the family moved to Curly Hill, Strabane when James was about 10. He was a fellow of Trinity College Dublin and a contemporary there of William Rowan Hamilton. In 1835 he was appointed to the Chair of Mathematics at Trinity.

Although he worked mostly on optics, he is also remembered for his work on geometry; his most significant work in optics was published in the mid-to-late 1830s; his most significant work on geometry On surfaces of the second order was published in 1843. he was awarded the Cunningham Medal of the Royal Irish Academy in 1838.[1]

In Passages from the Life of a Philosopher, Charles Babbage wrote that MacCullagh was "an excellent friend of mine" and discussed the benefits and drawbacks of the analytical engine with him.

MacCullagh's most important paper on optics, entitled "An essay towards a dynamical theory of crystalline reflection and refraction" was presented to the Royal Irish Academy in December 1839. The paper begins by defining what was then a new concept, subsequently, by transverse waves, he found that the potential function must be proportional to the squared norm of the curl of the displacement field. It was accepted that his radical choice ruled out any hope for a mechanical model for the ethereal medium. Nevertheless, the field equations stemming from this purely gyrostatic medium were shown to be in accord with all known laws, including those of Snell and Augustin-Jean Fresnel.

At several points, MacCullagh addresses the physical nature of an ethereal medium having such properties. Not surprisingly, he argues against a mechanical interpretation of the William Thomson, 1st Baron Kelvin succeeded in developing a physically realizable model of MacCullagh's rotationally elastic but translationally insensitive ether, consisting of gyrostats mounted on a framework of telescoping rods, described in his paper "On a Gyrostatic Adynamic Constitution for Ether" (1890).

MacCullagh died in Dublin at his own hand, perhaps depressed by what he saw as the decline of his mathematical powers.

In May 2009, an Ulster History Circle plaque was unveiled at his family tomb at St Patrick's Church in Upper Badoney. The plaque was part of events organised by the Glenelly Historical Society to mark his life.


  1. ^ Physicists of Ireland: Passion and Precision. p. 73. 

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