Wrote Letter L-043 of 1676-10-30 to Henry Oldenburg about his discussions with Grew and Boyle as well as the unreliability of the postal system
Text of the letter in the original Dutch and in English translation from Alle de Brieven. The Collected Letters at the DBNL - De Digitale Bibliotheek voor de Nederlandse Letteren
The original manuscript on two folio pages, written and signed by Leeuwenhoek, is preserved at the Royal Society (MS. 1853 Early Letters L1.24). On the outside, Leeuwenhoek wrote, "A Monsieur / Monsieur Grubendol / a. / Londres". Oldenburg added, "rec. le26. Oct. 76. / resp. le 2. Nov. que / j' escriray plus amplement / au plustost."
Leeuwenhoek wrote this letter to Henry Oldenburg about his discussions with Nehemiah Grew and Robert Boyle. He was pleased with Dr Grew's remarks, although he could not understand them, and when he gets the letter translated he will reply. He invites objections and those who point out his errors. The rest of the letter discussed the uncertainties created by the length of time it took from letters to go between Holland and England and the general unreliability of the system.
Leeuwenhoek began the short letter, not published until the 20th century, by noting that he had received no acknowledgement of his letter of 1676-05-29. It contained his disagreements with Nehemiah Grew, so Leeuwenhoek offered to send a copy if Oldenburg had never received it.
My previous letter was of the 9th inst. Since then I received your esteemed letter of the 8th, together with Transaction Nr. 1271, in which was inserted my letter of April 21st. I received both through a German friend, but neither from your letter nor from the Transaction could I learn whether you received my letter of May 29th. If the same has been lost I will send you a copy.
Who was that German friend? Perhaps Leibniz, who was in London in October, having traveled there to and from his home in Hanover via Holland.
Leeuwenhoek ended the letter with reference to his letter of 1676-10-09, which, Leeuwenhoek did not know, Oldenburg had received a day after he wrote the letter that Leeuwenhoek was replying to. In fact, Oldenburg had acknowledged Leeuwenhoek's letter of 1676-10-09 in his own letter of 1676-10-26 N.S., which was in transit.
I do not doubt that you did receive my letter aforesaid of the 9th inst. in which I write on the manifold living creatures in various waters, only I fear that you may be bored by the great multitude of notes, since I learn that you are very busy, and that you may lack the time to translate the same in order to communicate them to the Gentlemen Amateurs.
While we don't know whether Oldenburg was bored, it was not until the following February, spread over three meetings, that the Royal Society read Leeuwenhoek's groundbreaking letter. The following month, Oldenburg published only the first third or so of the letter in Philosophical Transactions. It was not until 6 months later that Robert Hooke verified Leeuwenhoek's observations of microbes.