Henry Oldenburg wrote to Leeuwenhoek encouraging him to send more observations

Date: 
August 20, 1674

This letter was probably a reply to Leeuwenhoek's letter of 1674-06-26. Leeuwenhoek mentioned it in his next letters, 1674-08-28 and 1674-10-09. Oldenburg relayed a message from Robert Boyle and encourged Leeuwenhoek to continue sending his observations.

Document: 

The manuscript is lost and the letter was never printed.