The Royal Society read part of Letter 48 of 1686-01-22 about the particles composing cinnabar

May 1, 1686

Birch, History, vol IV, p. 479, 21 April 1686 (O.S.) in London:

Part of a letter of Mr. LEEWENHOECK was read, wherein he described the particles composing cinnabar, shewing them to be made up mostly of hexagonal figures, yet not without the mixture of some sulphureous and saline particles, whose figures, as viewed in his microscope, he described.