Edmond Halley wrote Letter L-184 to Leeuwenhoek on behalf of the Royal Society, assuring him that the portraits he sent are received, wondering why he has not sent any observations recently, and enclosing recent numbers of Philosophical Transactions

This letter is known only by reference in Leeuwenhoek’s reply.

Someone from the Royal Society writes a courteous letter to Leeuwenhoek that the portraits he sent are received, wondering why he has not sent any observations recently, and enclosing recent numbers of Philosophical Transactions. There is a reference to a letter that Leeuwenhoek never received.

The date is New Style, which is ten days ahead of the Old Style date of 14 February used by the writer in London. The writer was possibly one of the Society’s two secretaries, Thomas Gale or John Hoskyns. However, given the references to the portrait and Colson in Edmond Halley’s Letter L-176 of 25 May 1686, the Society’s paid clerk Halley seems the probable writer.

Leeuwenhoek’s previous letter to the Royal Society is Letter L-178 of 10 July 1686. In the two years before that, he had sent an average of one letter every other month, so a seven-month drought was enough to cause the Royal Society to inquire about it. Even so, after this inquiry, Leeuwenhoek did not get another letter from the Royal Society until Letter L-215 of 12 February 1692 (dated 2 February 1692 O.S.) from Richard Waller. In addition, there is no record of the Royal Society’s reading one of Leeuwenhoek’s letters between 23 November 1687 O.S., Letter L-192 of 9 September 1687, and 13 January 1692 O.S., Letter L-212 of 27 November 1692.

During those years, Leeuwenhoek wrote 15 letters to the Royal Society. He published the first eight in Vervolg der Brieven, geschreven aan de Wytvermaarde Koninglijke Societeit tot Londen (Continuation of the letters, written to the well-known Royal Society in London) in 1687 and their Latin translations, Continuatio epistolarum (Continuation of the letters), in 1689. He published the last seven in Natuurs Verborgentheden Ontdekt: zijnde een Tweede Vervolg der Brieven (Nature’s secrets discovered: being the second continuation of the letters) in 1689, which made up the first half of Arcana Naturae Detecta (The secrets of nature discovered) in 1695. These letters contain, among many other things, Leeuwenhoek’s proof of William Harvey’s theories about circulation of blood and the design, construction, and use of the eel viewer (aalkijker) that he used as his showcase demonstration for visitors. Only one of these 15 letters was published in Philosophical Transactions, but not until 1694.

If by “last year”, Leeuwenhoek meant volume 16 of Philosophical Transactions, it was edited by Halley and contains no letters by Leeuwenhoek. His previous publication there is in vol. 15, no. 174, in 1685, edited by William Musgrave, and the following is seven years later in vol. 17, no. 196, in 1693, edited by Richard Waller.