Letter, from Henry Oldenburg to Jean Cassini, dated at London That Brouncker had been shown Cassini's paper on the sunspots; encloses pages of Boyle's observations of the sunspots made in 1660; concerning Huygens' 'Systema Saturnium'; concerning observations of the occultation of Saturn by the moon by Hevelius; postscript that Monsieur Picard had observed the sunspots in 1661 and that some English astronomers had just observed a sunspot on 25 August 1671 26 August 1671