Letter, from Antoni van Leeuwenhoek to the Royal Society, dated at Delft Signed autograph Observations of amber; observations of 'burned paper' from the sky (in retrospect is dried-up algal) (sample was enclosed with letter); observations of rotifers (microscopic aquatic animals), maggots, blow flies and the possibilities of their reproduction; the stinging hairs of nettles; observations of the East-Indian centipede 11 original figures no longer exist; engraved figures for publication are attached Three small packets of specimens were attached to the final sheet of letter, now stored separately in an envelope. The packets are labelled: 1. 'paper which in 1686, 14 or 15 March in Courland, was said to have fallen from the sky'; 2. 'dried film which covered the suppled paper found in Courlant, having fallen from the sky'; 3. 'Film which lay adrift in a barrel, dried on paper'.The original packets still contain >70% of the original material. The rest was separated in three portions in 1981 by Brian Ford, a first portion was placed in separate packets, kept in an envelope; a second portion of the samples were sputtered in gold and are kept in a separate container; a third portion of the algal specimens were wet-teased and kept in a slide-box. Transcribed and translated in 'Alle de brieven van Antoni van Leeuwenhoek', edited, illustrated and annotated by Committee of Dutch Scientists, vol 7, p 81 See 'The van Leeuwenhoek specimens' by Brian Ford in 'Notes and Records', vol 36, no 1, pp 37-59 at p 48 for further information 17 October 1687