The date is established by the publication at the beginning of May 1839 of William Whewell’s presidential address to the Geological Society of London (see n. 2, below). The last Saturday in April 1839 was 27 April.

Immediately after Whewell delivered his presidential address to the Geological Society of London on 15 February 1839, CD had asked him to make his comments on the delay in publishing CD’s researches from the Beagle voyage less pointed to avoid annoying the Beagle’s captain, Robert FitzRoy (Correspondence vol. 2, letter to William Whewell, 16 February [1839]). It is likely that CD was returning a page proof of the revised address to Lonsdale, the society’s assistant secretary and librarian. The further minor correction requested here appears in the address as published in the society’s Proceedings, which reads: ‘In speaking of Mr. Darwin’s researches I cannot refrain from expressing for myself, and I am sure I may add for you, our disappointment and regret that the publication of Mr. Darwin’s journal has not yet taken place. Knowing, as we do, that this journal contains many valuable contributions to science, we cannot help lamenting, that the customs of the Service by which the survey was conducted have not yet allowed this portion of the account of its results to be given to the world’ (Whewell 1839, p. 93). The final version of the passage was also reprinted in Philosophical Magazine 3d ser. 14 (1839): 503, in the issue for May 1839. CD’s Journal and remarks was in print in early 1838, but was not published until late May or early June 1839 (Freeman 1977).