The Royal Society ordered that Letter 49 of 1686-04-02 be translated

April 24, 1686

Birch, History, vol IV, p. 473, 14 April 1686 (O.S.) in London:

A letter of Mr. LEEWENHOECK, dated April 2, 1686, N.S. being an answer to one sent him dated March 2, O.S. and giving an account, among other things, of the texture of bone viewed in a microscope, was produced, and ordered to be translated.