Henry Oldenburg wrote Letter L-042 to Leeuwenhoek acknowledging receipt of the letter of 1676-10-09
This letter is known only by reference in another letter.
Oldenburg received Letter L-040 when it was October 9 in London, October 19 in Delft. It thus took ten days to reach him. He responded a week later, on October 16, which was October 26 in Delft. He wrote that he received the letter but had not had time to study it in detail.
The reference to Leibniz is puzzling. In October 1676, Leibnitz had recently arrived in England from Holland and was about to return to Germany via a visit to Dutch philosopher Baruch Spinoza in The Hague, only a few miles from Delft. Perhaps Oldenburg used the occasion to send his 16 October acknowledgment via Leibnitz, who would have been very interested in the little animals that L. reported in Letter L-040 of 9 October.
This letter is calendared as Letter 2991 in Hall and Hall, The Correspondence of Henry Oldenburg, vol. XIII, July 1676 – July 1681, p. 107.
At the end of Leeuwenhoek's Letter 18 of 1676-10-09, Oldenburg wrote this note in French:
receu le 9. Octob. st. v. 1676.
Resp. le 16. Oct. d'avoir
receu cette lettre, par
M. Leibnitz, mais non pas
encor consideré.
st. v. - old style (Julian)