Wrote Letter L-181 of 1686-09-10 to Antonio Magliabechi, a cover letter for a copy of one of his books

September 10, 1686
Standard reference information
Collected Letters volume: 

With this letter, L. sends Magliabechi a copy of a recent publication through a common friend, Daniël Papenbroek. The letter is known only by reference in another letter.

Letter L-182 of 30 October 1686 to Antonio Magliabechi

… my missive of the 14th April …. Since which time I have again made some slight observations and had them printed; these I sent on the 10th of last month to the Rev. Father Papenbroek, with the added request to forward the same at his early convenience to you, most ill., highly learned and very renowned sir.

This letter and the printed volume to Antonio Magliabechi accompanied Letter L-180 of 10 September 1686, to Daniël Papenbroek, a Jesuit priest from Antwerp.

Leeuwenhoek is mistaken about the date of 14 April. Since his previous Letter L-174 of 12 April 1686 he had published only in Dutch, a language that Magliabechi did not know. The “slight observations” that Leeuwenhoek had printed were clearly a separate publication from the one referred to earlier in Letter L-182. See Letter L-172 of 16 March 1686. Leeuwenhoek's next publication in Latin, a language that Magliabechi could read, was in 1687, so perhaps he sent one of the two Dutch publications in 1686, both printed by Cornelis Boutesteyn in Leiden.

Collected Letters, vol. 6, p. 177, n. 6 says that L. sent this volume: Ontledingen en ontdekkingen, van de cinnaber naturalis, van het been en huyd, etc. (Analyses and discoveries of natural cinnabar, of bone and skin, etc.) contains five letters: Letter L-168 of 22 January 1686 and Letter L-173 of 2 April 1686 through Letter L-178 of 10 July 1686. All of these letters were written to the Royal Society.

The other possibility is Ontledingen en Ontdekkingen van Levende Dierkens in de Teel-deelen van verscheyde Dieren, Vogelen en Visschen etc. (Analyses and discoveries of living animals in the generative parts of various animals, birds, and fish etc.), which contains seven letters: Letter L-080 of 25 April 1679 through Letter L-106 of 13 May 1680 and Letter L-114 of 4 November 1681 through Letter 68 [36] of 4 April 1682. All of these letters were also written to the Royal Society.