Visited by Gottfried Leibniz

November 18, 1676

While in England, Leibniz spent time with Henry Oldenburg, who no doubt told him about Leeuwenhoek's recent observations of little animals in infusions. At the end of Leeuwenhoek's letter of 9 October reporting on the little animals, Oldenburg wrote a note suggesting that he had entrusted his reply of 16 October (O.S.) with Leibniz to deliver to Leeuwenhoek. 

On his way back to Germany from England, Leibniz spent a few days in the Dutch Republic. While in the Republic, he met both Spinoza in nearby Voorburg, a village between Delft and Den Haag, and Leeuwenhoek in Delft. Leeuwenhoek showed him the little animals in some of the infusions about which he had written to the Royal Society six weeks earlier, in October. 

A few days after his visit, Leibniz reported back to Oldenburg, "I took great delight in Leeuwenhoek's observations, and I wish that many others were moved by the same curiosity, as this would bear great fruit for the physics [rei physicae] to come. The spectacle of the little worms that pepper and other spices caused to form in water was delightful."

More than 20 years later in a letter to former Delft mayor Hendrik van Bleyswijk, Leibniz wrote that Leeuwenhoek "must not be young anymore because I saw his workspace about 20 years ago".