Henry Oldenburg wrote to Leeuwenhoek for more details about his method for observing little animals

February 22, 1677

Written on February 12 O.S. in London.

When the Royal Society read and discussed over three meetings Leeuwenhoek's long letter of 1676-10-09, they found his observations so unexpected as to be unbelievable. They asked Oldenburg to ask Leeuwenhoek for details about how he made his observations. Although this letter is lost, Leeuwenhoek mentioned it in his reply 1677-03-23.