The date range is conjectured from those years when CD and Falconer were on visiting terms and when Falconer was resident in London. CD visited Falconer from at least 1845, and possibly from as early as 1843; they met in London in June 1847 (see Correspondence vol. 4, letter to J. D. Hooker, [10 June 1847]); Falconer left for Calcutta in 1848 and returned to settle in London early in 1857. CD visited him in London in 1857 and 1858 but they did not meet again until at least November 1859 (see Correspondence vol. 6, letter to J. D. Dana, 5 April [1857]; Correspondence vol. 7, letter from Hugh Falconer, 25 October and 12 November [1859]). They met again in London in August 1860 and May 1862 (Correspondence vol. 8, letter to Charles Lyell, 28 August [1860]; Correspondence vol. 10, letter to J. D. Hooker, 9 May [1862]). In October 1862 CD wrote to Falconer: ‘I had hoped to have called on you on Monday evening, but was quite knocked up’ (Correspondence vol. 10, letter to Hugh Falconer, 1 October [1862]). They may have met when CD was in London in February 1863 (see Correspondence vol. 11, letter to Hugh Falconer, 20 [January 1863]). No further meeting are known to have taken place before Falconer’s death early in February 1865. CD was not in London in January 1865.

CD complained of swimming of the head from mid-1848 to spring 1849, in 1854, February 1859, and September 1863 (see Correspondence vol. 4, letter to J. S. Henslow, 6 May 1849, Correspondence vol. 5, letter to Edward Sabine, 28 June [1854], Correspondence vol. 7, letter to W. D. Fox, [12 February 1859], and Emma Darwin’s diary (DAR 242)).