Elizabeth Hungerford Keate Macie was a cousin of the 1st Duke of Northumberland's wife Elizabeth Seymour, and an heiress in her own right, to the property of the Hungerfords of Studley. She was also the widow of John Macie, of Weston, near Bath, Somerset; so the young James Smithson originally was called Jacques Louis Macie. Elizabeth later married John Marshe Dickinson, a troubled son of Marshe Dickinson who was Lord Mayor of the City of London in 1757 and Member of Parliament. During this marriage, she had another son, called Henry Louis Dickenson; but the 1st Duke of Northumberland, rather than Dickinson, is thought to have been the father of this second son also.
Source: http://en.wikipedia.org/wiki/James_Smithson