William Emerson was an architect.
He may have known JW in the mid-seventies, when his name appears in an address book (#12714). He was the President of the Royal Society of British Artists from 1899-1902 (JW had been President briefly, until 1888).
Jopling, Louise, Twenty Years of My Life, 1867 to 1887, London, 1925; Who Was Who: A Companion to Who's Who, vol. 2, 1916-1928, London, 1942; Who was who: a cumulated index, 1897-1990, London, 1991.