This bust bears a 'PS' monogram which is likely to relate to Peter Slater of Edinburgh (b. 1809) who attended the Royal Academy schools in 1831 on the recommendation of W. Collins, R.A. In 1853 he was commissioned to make a copy of Chantrey's statue of James Watt for Adams Square in Edinburgh. Slater exhibited at the Royal Academy, 1846-1870, showing mainly busts of Scottish worthies.
(R. Gunnis, Dictionary of British Sculptors, London, rev.ed., 1968, pp. 353-354).