Letter, from Jean Dominique Cassini to Henry Oldenburg, dated at Paris Cassini says that he sends a copy of his observations of the sunspots, then gives details of his observations of Saturn, and informs Oldenburg that Monsieur Picard was going to Tycho Brahe's observatory on the island of Hven in the Danish Sound to observe the lunar eclipse and the difference between the meridians and the height of the Pole Read to the Royal Society on 2 November 1671 20 August 1671