Letter, from Francis Vernon to Henry Oldenburg, dated at Paris Concerning work at the Royal Academy of Sciences in Paris: on the nature of gravity, on the herbal of Marchand and Duclos, Beaugrands' 'Lexicon geographicum', a new star in the constellation 'Cygnus'; mentioning, Cassini, Auzout, Molin, Huygens; mentioning Wallis's new clock with a pendulum 19 July 1670