Abercromby (1745-95) was a Scottish lawyer and essayist.
NGV 1905 indicates Raeburn as the source. However, another impression, in the National Portrait Gallery, London (reproduced below), is listed as after an unknown artist.
[photo reproduced below: National Portrait Gallery impression]
NGV 1865, p.82 (artist/s not named); AR 1870-71, p.34: Engravings (framed); NGV 1894, p.107 (V.Buvelot Gallery, 2nd bay, no.23: as by Dawe); NGV 1905, p.119 (V.Buvelot Gallery, 2nd bay, no.13: as after Raeburn)
For the impression shown here (NPG D7130, purchased 1966), see http://www.npg.org.uk/collections/search/portraitLarge/mw41140/Alexander-Abercromby-Lord-Abercromby?LinkID=mp50181&role=sit&rNo=0