The Royal Society received Leeuwenhoek's first letter

Date: 
May 7, 1673

Mr. OLDENBURG produced a book of Dr. de GRAAF dedicated to the Society, intitled, Regneri de Graaf Partium Genitalium Defensio, together with a letter to Mr. OLDENBURG, dated at Delft in Holland, 28th April, 1673, communicating some microscopical observations of Mons. LEEWENHOECK.

The Dutch Republic was using the new Gregorian calendar, so it was May 17 in Delft when the letter was received. Even if the letter was not read aloud at the meeting, the members read it a few weeks later when Oldenburg published his translation in the next issue Philosophical Transactions, number 94, dated May 19, 1673.

One of the attendees at that meeting was not a member of the Royal Society.

Signor BOCCONE, a Sicilian gentleman, who was well skilled in plants and petrifications.

Later on his tour of Europe, botanist Paolo Boccone (1633-1704) visited Leeuwenhoek (source: Con. Huygens).

Document: 

Birch's History, vol. III, p 88

Sources
Year Author Title
1667 Sprat, T. History of the Royal Society of London
1673 Leeuwenhoek, A. van A Specimen of Some Observations Made by a Microscope, Contrived by M. Leewenhoeck in Holland, Lately Communicated by Dr. Regnerus de Graaf
1756 Birch, T. The History of the Royal Society of London