Cockle is also remembered for his mathematical and scientific investigations. For instance he invented the number systems of tessarines and coquaternions, and worked with Arthur Cayley (1821–1895) on the theory of linear algebra. Like many young mathematicians he attacked the problem of solving the quintic equation, notwithstanding Abel–Ruffini theorem that a solution by radicals was impossible. In this field Cockle achieved some notable results, amongst which is his reproduction of Sir William R. Hamilton's modification of Abel's theorem. Algebraic forms were a favourite object of his studies. He also made contributions to the theory of differential equations,[3] in particular the development of the theory of differential invariants or criticoids.[6]
An obituary notice by the Revd. Robert Harley was published in 1895 in Proc. Roy. Soc. vol. 59. A volume containing his scientific and mathematical researches made during the years 1864–1877 was presented to the British Museum in 1897 by his widow.[3] Like his father, Cockle became wealthy during his lifetime, leaving an estate of £32,169, which is approximately £2.7 million if adjusted for inflation as of 2008.[7]
Cockle also wrote a series "Method of Vanishing Groups" for the Cambridge and Dublin Mathematical Journal, volumes and pages 2: 267 to 73, 3: 179 to 81, and 4: 174 to 78.
