Wrote Letter L-129 of 1683-07-22 to Anthonie Heinsius about Heinsius's reactions to an earlier letter
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 one octavo page, written and signed by Leeuwenhoek, is preserved at the Rijksarchief (National Archive) in Den Haag (Inv. No. 13). The letter was not published during his lifetime.
The letter was a cover letter to the copy of Letter L-128 of 16 July 1683, written to Christopher Wren and copied by Adriaan Lansveld.
Leeuwenhoek wrote that he was happy that Heinsius was pleased with his speculations and investigations, presumably referring to Letter L-126 of the previous May.