With the sketchbook inverted, Turner has used this page to copy out his own address. The artist tore out at least one page from this notebook (between folios 51 and 52; D25621, D25623) and he may have intended to tear out this page to give to someone, or else just used the page to show someone his address to copy down. Writing his address in the sketchbook may have been a precaution in case the book was lost, although if this was his intention it is strange that he did not use the front or back page instead.1
Turner seems to have moved into 47 Queen Anne Street West in 1809, and kept it as his home and gallery for the rest of his life (though from 1846 he lived in Cheyne Walk, Chelsea).2
It is interesting to point out that Turner noted down Robert Cadell’s address in the Berwick sketchbook (Tate D25656; Turner Bequest CCLXV 8a).
James Hamilton, ‘Queen Anne Street West’, Evelyn Joll, Martin Butlin and Luke Herrmann (eds.), The Oxford Companion to J.M.W. Turner, Oxford 2001, p..