The year is established by the relationship between this letter and the letter from Reginald Darwin, 7 April 1879.

Cambridge University Library was known as the public library; in this context, ‘public’ was used in the sense of ‘Belonging to ... the whole university (as distinguished from the colleges or other constituents)’ (OED). Andrew Duncan had published a memoir of Henry Raeburn, in which he made clear that Raeburn had not painted a portrait of Erasmus Darwin’s eldest son, Charles Darwin (1758–78), but had made a trinket in which he set a lock of Charles’s hair (Duncan 1824, pp. 10–12). L. Library: London Library. There was a copy of Portraits by Sir Henry Raeburn (1876) with a biographical essay by John Brown (1810–82) in Cambridge University Library, but this made no mention of Charles Darwin (Brown 1873). The Life of Sir Henry Raeburn, R.A. was not published until 1886 (Andrew 1886).

Reginald Darwin had given this reference to CD (see letter from Reginald Darwin, 7 April 1879).