Letter, from Henry Oldenburg to [Christiaan] Huygens, dated at London Concerns publishing Cassini's observations of Saturn, and that Oldenburg will send this together with Hevelius's observations of Saturn, Jupiter's satellites, transit of Saturn; discussing Newton's new telescope; concerning Smethwick's work on nonspherical lenses; that he will send Slusius' account of his construction of Alhazen's problem at a later date; that he sends an account of Moreland's trumpet and wishes for comments on it 1 January 1672