The Heaths were an English family of artists. H. Heath was active in the 19th century.
George Humphrey took over the printselling business of Hannah Humphrey, which was begun in the late 18th Century, trading as G. Humphrey from 1820-1830.
Maxted, Ian. “The London book trades 1775-1800: a preliminary checklist of members.” Exeter Working Papers in British Book Trade History. 2001. http://www.devon.gov.uk/library/locstudy/bookhist/lonh.html (15 April 2002).