Wrote Letter L-519, now lost, of sometime before August 1715 to Gottfried Leibniz about his observations and recent letters
This letter is known only by reference in another letter.
In this letter, Leeuwenhoek sends his observations and mentions recent letters that were not published until the Send-Brieven of 1718.
Letter L-520 of 5 August 1715 from Gottfried Leibniz
Apart from that I should like to express my wish that Your Honour will proceed with the publication of your Sendbrieven, and will further inform the world of your observations. Yes, I would wish that Your Honour presents a Systema Phytorum, although not in all certain; for such people like you are not to be overlooked.
The lost letter from Leeuwenhoek that Leibniz is replying to in Letter L-520 of 5 August 1715 must have mentioned the collection of recent letters that ended up in Leeuwenhoek’s Send-Brieven, published three years later. In Leeuwenhoek’s reply, Letter L-521 of 28 September 1715, he wrote:
I intend to have nothing printed in our language, but after my death more than a hundred letters will be made generally known in print and to that end, I have already ordered eleven copper plates to be cut; so that now nothing is published but what I write to the Royal Society in London, and that is in the English language.
However, when this letter was published in Send-Brieven, Leeuwenhoek added a footnote on p. 168
On the recommendation of good friends, I have changed my intentions.
For the fate of these hundred letters, see Lens on Leeuwenhoek https://lensonleeuwenhoek.net/content/what-happened-papers.
Leibniz’s reference to a “Systema Phytorum” is unclear, though he may mean a treatise that synthesizes the observations on a given subject scattered through Leeuwenhoek's letters.
Although Leibniz visited Leeuwenhoek in 1676, there are no known letters between them until perhaps Letter L-312 of 1697, which may have been a reply to lost letter from Leeuwenhoek. With the present lost letter, Leeuwenhoek seems to have initiated the resumed correspondence almost two decades later. Leibniz’s Letter L-520 of 5 August 1715 about sperm and encouraging young people seems to be a reply. The exchange of letters continued with Leeuwenhoek’s Letter L-521 of 28 September 1715 and Leibniz’s reply, Letter L-522 of 29 October 1715 about Leeuwenhoek’s observations and about teaching his methods.
On the topic of encouraging Leeuwenhoek to share his methods with students, Leibniz had an exchange of letters in French with Hendrik van Bleyswijk in 1697 and 1698. As a former Delft magistrate and mayor, Bleyswijk had worked with Leeuwenhoek in Delft’s city hall for thirty years. His correspondence with Leibniz is found in Leibniz’s Allgemeiner Politischer und Historischer Briefwechsel (General political and historical correspondence), vol. 14, May-December 1697, and vol. 15, January-September 1698.
