The identity of Granville Cole is not certain.
In the 1881 census, one Granville Cole 'gentleman', is listed, aged 27, born in London; he was then living at 36 Welbeck Street.
Charles Buller Granville Cole (1854-1901), was an unmarried son of Sir Henry Cole and younger brother of JW's friend A. S. Cole. The spelling of his name is not absolutely certain, since 'Grenville Cole' was noted in 1881 as a consulting chemist to Spence's Metal Manufacturing Company Ltd.
A third possibility is Arthur James Grenville Cole (1859-1924), a geologist. He was born on 21 October 1859 and died on 20 April 1924. He was the son of the architect J. J. Cole, and married Blanche Vernon. He was educated at the City of London School and Royal School of Mining, and became a Professor of Geology and a prolific writer. He became an FRS in 1917, was at the Royal College of Science for Ireland 1890-1924, and was Director of the Geological Survey of Ireland, 1905-1924.
UK census 1881; Times, London, Saturday 16 April 1881, p. 4; Times, London, Monday, 24 April 1882, p. 8; Kelly's London Post office Directory, London, 1881; Times, London, Tuesday, 22 April 1924, p. 18.