In 1912 Eddington led an expedition from the Royal Observatory to Brazil to observe and photograph a total eclipse of the sun. These letters contain an account of the expedition. Eddington specifically asked his mother to preserve the letters because he was keeping no other record of events (see A2/5), and she seems to have been careful in carrying out his request, as the sequence is probably complete. The letters are numbered from 1 to 9 in a contemporary hand, and the ninth letter, finished when the writer was about three days’ sail from home, was almost certainly the last. These letters formed the basis of the account in Eddington’s Notebook (ff. 96–102), and they were consulted by Douglas, who quoted from A2/8 (pp. 18–19).
Eddington and his assistants C. R. Davidson and J. J. Atkinson left Southampton aboard the steamship Arlanza on 30 August and arrived at Rio de Janeiro on 16 September, where they were joined by T. N. Lee, an Englishman deputed by the Brazilian Government to assist them, and J. H. Worthington, an amateur astronomer. Six days later the party arrived at Passa Quatro, their chosen observation point—preferred to other possible sites at Cruxeiro, Christina, and Alfenas—and on 3 October they were joined by two volunteers, Leslie Andrews and O. Couto de Aguirre. A local man, Pierre Seux, also volunteered to help by counting seconds during totality. The eclipse took place on the 10th, but unfortunately observations of the phenomenon were prevented by rain and the expedition was largely unsuccessful. Eddington and his companions left Passa Quatro on 20 October and sailed for home on the Danube on the 23rd. The date of their arrival in England is not recorded, but towards the end of the voyage they were expecting to be at Southampton on 10 November. A report of the expedition, by Eddington and Davidson, was printed in MNRAS (lxxiii, 386–90) the following year. Notes also appeared in The Observatory, xxxv (1912), 328–30, 410, and xxxvi (1913), 62–5.