Henry Oldenburg wrote Letter L-025 to Leeuwenhoek recommending that he get help from knowledgable people
Because this letter is lost, it is known only by reference in Leeuwenhoek’s reply.
In this letter, Henry Oldenburg acknowledges the receipt of Leeuwenhoek's letter of 26 March 1675 and praises him. He also recommends that L. ask other people to help him understand what he sees through his lenses.
This letter is calendared as Letter 2643 in Hall and Hall, The Correspondence of Henry Oldenburg, vol. XI, May 1674–September 1675, p. 275.
Leeuwenhoek's reply, Letter L-026 of 14 August 1675 to Henry Oldenburg:
I duly received your agreeable letter of April 12th ultimo. I was glad to see from it that my slight observations in my letter of March 26th pleased you so much; also your unmerited friendly disposition towards me. ... You recommend me to call in the assistance of other persons, capable of judging of such things. Allow me to say, Sir, that there are very few people in this town that could assist me, and as to people that come to visit me from other places, well, recently I had one here who rather intended to dress himself in plumage borrowed from me, than to lend me a helping hand.