Letter, from Antoni van Leeuwenhoek to the Royal Society, dated at Delft Signed autograph Observations of plaster, alabaster, plaster stone from France, gypsum, Muscovite glass, cobblestone, shell lime, masonry mortar, lime, cement, sand stone, slate Original figures no longer exist; engraved figures for publication are attached Transcribed and translated in 'Alle de brieven van Antoni van Leeuwenhoek', edited, illustrated and annotated by Committee of Dutch Scientists, vol 7, p 279 3 August 1688