Henry Oldenburg wrote Letter L-030 to Leeuwenhoek about the reaction in London to his observations
When Oldenburg wrote this letter on 28 December 1675 in London, it was 7 January 1676 in Holland. It is known only by reference in Leeuwenhoek’s reply.
This letter is calendared as Letter 2811 in Hall and Hall, The Correspondence of Henry Oldenburg, vol. XII, October 1675 – July 1676, p. 116.
In this letter, Henry Oldenburg writes in the French language that he assumes Leeuwenhoek knows. Oldenburg relates that the members of the Royal Society had no opinion about Leeuwenhoek’s latest observations and that he would send more issues of Philosophical Transactions, but he fears the postage will be too expensive.
Letter L-031 of 22 January 1676 to Henry Oldenburg. Oldenburg must have written it in French, because Leeuwenhoek replied:
Your letter of the 28th was received by me in good order, from which I learned that you do not doubt my knowledge of French, but I must tell you that I regret I do not understand any language but Dutch and when you write to me in French or Latin I can help myself all right, since I have enough friends who will translate it for me; but I cannot help myself with the English language since the death of a certain gentleman who was proficient in this language.